How to Add an Air Duct to a Room

This photo tutorial explains how to add a room air duct for heating and cooling by installing a flexible air duct and vent for better air flow.

Room Heating and Cooling Problem

My daughter’s bedroom was too warm in the summer and too cold in the winter because it had just a single air duct from the central heating and air system. By comparison, my son’s bedroom is about the same square footage and has two supply air ducts that keeps it comfortable year round. I installed a second air vent to the ductwork for my daughter’s bedroom:

HVAC Flexible Air Duct Branch Line

HVAC Flexible Air Duct Branch Line

Air Handler and Duct Work Problems

A large number of residential Heating Ventilation and Air Conditioning (HVAC) systems are poorly designed and/or installed. The problems I’ve found in my home are:

  • Blown fiberglass insulation (the white fluffy stuff that looks like cotton) was piled up near the scuttle hole entrance in the attic over my daughter’s bedroom and the far side of the attic had little or no insulation. Proper insulation is essential for climate control.
  • Dirty AC evaporator coils. Dirty air handler evaporator coils will block the air flow, decrease system efficiency and run up your electric bill.
  • Dirty or clogged air filter. Change the air filter regularly because a dirty filter will block the air flow.
  • Pinched, loose or disconnected flexible air ducts have a huge impact and waste energy.

If you have any of the above problems with your central air system, try fixing those problems first.

How to Add an Air Duct to a Room

Speedi-Boot – A Faster and Better Way to install a new air vent.

Please see this newer project for a faster and better way to install a room air vent using Speedi-Boot.

The remainder of this article explains how to install an air vent using a conventional vent boot.

Flexible Air Duct Branch Line Installation Materials

Flexible Air Duct Branch Line Installation Materials

The materials for the six inch diameter branch line cost about $60 at Home Depot:

  1. Starting Collar – 6 inch diameter
  2. Insulated Flexible Duct – 6 inch diameter, 25 feet length
  3. Register Box (a.k.a. “vent boot”) – 6 in by 10 in
  4. Register Grille – 6 in by 10 in
  5. Metal Foil Tape – one roll
  6. Nylon Zip Ties – 36 inch

Air Duct Installation Tools

The tools needed for this project are:

Duct Work Installation Guide and Tips

The Duct Work chapter from Heating and Cooling Essentials by Jerry Killinger is an excellent introduction to duct work operation, materials and installation.

How to Install a Ceiling Air Vent

The first task is to locate the new vent boot on the ceiling. I measured the existing ceiling register and plotted the new register in an identical position on the right side of the room. A carpenters square is used to draw a perfect 6″ by 10″ outline on the ceiling where the new hole will be cut for the air vent.

I relied on the regular spacing of the ceiling joists such that the register box would be in the gap between the ceiling joists. Before cutting the drywall, I drove a finishing nail into the ceiling to verify there were no joists, making a series of small holes as shown below. If I made a mistake in the position of the register box, it’s easy to patch the small hole made by a finishing nail. A stud finder could be used.

Install an Air Vent: Ceiling Register Outline 6" x 10"

Install an Air Vent: Ceiling Register Outline 6″ x 10″

A Rotozip spiral saw is used to cut the drywall for the ceiling register. Tip: Have a helper hold a vacuum cleaner hose up to the saw to catch most of the dust.

Install an Air Vent: Drywall Ceiling Cutout

Install an Air Vent: Drywall Ceiling Cutout

I left the drywall panel in place to prevent the attic insulation from falling into the room. I’ll remove the panel after the insulation is cleared away in the attic.

Ceiling Drywall Cutout for the New Air Vent

Ceiling Drywall Cutout for the New Air Vent

Now it’s time to go into the attic.

Attic Access for Ductwork

Be extremely careful while working in the attic. Step only on the joists because the drywall under the insulation will not support your body weight – you can fall through the ceiling – resulting in injury or at least a messy drywall repair.

The attic gets very hot in the summer and you can quickly over heat. It’s best to work very early in the morning before it gets hot.

I needed to go into the attic to install the register box and flexible air duct. But I found there was a problem – I couldn’t get to the attic above the bedroom because the roof deck over the main house didn’t leave enough room to squeeze my 215 lb frame through the scuttle hole. Crawling wasn’t an option due to the risk of falling through the ceiling.

Flexible Duct to Attic above the Bedroom

Flexible Duct to Attic above the Bedroom

To solve the problem, I cut the roof deck with a handsaw and sabre saw as shown in the photo below. This allowed me to crouch and slide through with ample handholds while walking on the ceiling joists.

Roof Deck Scuttle Hole Cutout

Roof Deck Scuttle Hole Cutout

View of the attic scuttle hole looking back to the main house:

Attic Scuttle Hole

Attic Scuttle Hole

Here’s the insulation problem I found – mounds of it were on the left, but little or no insulation was over the rear areas of the attic above the bedroom. I redistributed the insulation evenly over the attic.

Blown-in Insulation Mounded in the Attic

Blown-in Insulation Mounded in the Attic

This project is continued in How to Add an Air Duct to a Room – Part 2.

Take care,

Bob Jackson

Copyright © 2014 HandymanHowTo.com   Reproduction strictly prohibited.

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87 Responses to How to Add an Air Duct to a Room

  1. Lucy July 12, 2009 at 11:35 pm #

    Can this be done with a first story room? Our Master bedroom is big and only has two air vents on one end and it stays hot during the summer and cold in winter since the air doesn’t circulate. Would it be possible to do this? can we run the air from the other two ducts?

    Thank you,

    Lucy

  2. Bob Jackson July 13, 2009 at 7:06 am #

    I need to know more about your house and the arrangement of the central air system to say with certainty.

    Are the A/C registers on the floor or ceiling? If you have a basement and the ducts are routed under the floor, you should be able to run a new branch line and install a register. You’ll have to cut a hole in the floor of course for the register.

    Lucy wrote:
    > can we run the air from the other two ducts?
    I don’t think you’d be happy splitting an existing branch line as it won’t increase the overall air volume significantly. A new branch line from the main trunk will increase the volume of air and make a real difference in comfort.

  3. David July 16, 2009 at 10:45 am #

    Do I need to check my AC unit to determine if it can handle another air duct???

  4. Bob Jackson July 16, 2009 at 11:37 am #

    Central A/C units are sized for the *square footage* of the house and adding a new duct shouldn’t be a problem. The important thing is to run the new branch extension from the main trunk line as I’ve shown here.

    Take a look at the GAF Installation Tips at this link (also referenced in the main article above): http://www.gaf.com/Content/GAF/METALDUCT/LLBP_Duct_Installation.html

  5. Keyosha July 20, 2009 at 12:35 pm #

    I bought a home where the previous owners put an addition over the garage which is now a large extra bedroom in the house. They had a wall unit heater installed which is extremely ancient, and running it increased our electricity bill by alot. There are no existing vents going to this room, but rather than replacing the wall unit, I would like to install air duct vents into this room, is that possible?

  6. Bob Jackson July 20, 2009 at 5:01 pm #

    You should be able to work something out. It’s difficult to give specific advice without knowing the details of the house construction. Do you have an attic over this new addition? Some pictures of your A/C system ductwork and attic areas would help – post them on http://tinypic.com

  7. josh hart July 22, 2009 at 3:14 pm #

    I have a room similar to yours in the l wing of my house in Florida, this room seems to be much warmer (5-10 degrees) especially if there is no fans running. I have been told that a return air vent would work better than adding a register. I have also heard that reducing the size of the duct running to that room with help as it is a thicker diameter than other bedrooms in the house. Supposedly the smaller size keeps the air flow higher and thus cooler the room better. What do you suppose is the best solution to getting this room as cool as the rest of the house?

  8. Bob Jackson July 22, 2009 at 6:06 pm #

    To determine if the room needs a new return vent, open the door about 1/2 inch. Is the room still warm after 30 minutes? If it’s warm, you don’t need an additional return vent (assuming you already have at least one), but a new cold air supply vent.

    The effect of opening the door about 1/2 inch is to mimic the effect of a new return vent by giving the air an escape route; at the same time the door is *almost* closed such that cold air from the main house doesn’t spill into the room.

    > I have also heard that reducing the size of the duct
    > running to that room with help as it is a thicker
    > diameter than other bedrooms in the house.
    Sounds like the installer knew the room needed a larger air supply and therefore used a larger diameter (“thicker”) duct.

    > Supposedly the smaller size keeps the air flow higher and
    > thus cooler the room better.
    You don’t want to do this – a smaller duct means lower air volume. The air velocity may be a bit faster through a small duct pipe, but friction losses in a small duct will defeat your goal. Bernoulli’s Principle explains the physics of air flow. See the pipe animation at http://home.earthlink.net/~mmc1919/venturi.html

    To get more air use the same or larger size flexible duct pipe and be sure to tap off the main trunk line. It wouldn’t hurt to consult with a HVAC technician.

    Living in Florida means hot summers and lots of solar heating of the roof over this room. Have you checked the attic insulation? Adding the R-30 fiberglass insulation as I’ve shown here really improved the thermal stability of the room. Less heat coming in means less A/C is needed to keep it comfortable.

  9. Dale Wilbanks December 5, 2009 at 8:36 am #

    Thanks Bob, just what I needed to get my daughter’s new bedroom done this morning!

    • Bob Jackson December 5, 2009 at 10:08 am #

      Wonderful! Thanks for letting me know. – Bob Jackson

  10. bill February 28, 2010 at 8:27 pm #

    If installing a flexible duct, can I squeeze it to get it through a tight space and still get adequate airflow? I need to get a 6″ diameter through at 4″ opening and an 8 inch diameter through a 5 1/2″ opening?

    • Bob Jackson February 28, 2010 at 9:26 pm #

      That’s not a good idea because a 6 inch duct has 28.27 square inches of capacity versus a 12.5 square inches for a 4 inch duct – that’s more than a 50% reduction in duct capacity. Same issue for pinching an 8″ duct through a 5-1/2″ opening. The area of a circle (the duct capacity) varies with the square of the radius by the formula: Area = 3.14 * Radius^2.

      What is the obstacle that requires the smaller opening? Is there no way to route around the obstacle or modify the opening to accommodate the larger duct?

  11. Nick April 20, 2010 at 6:09 pm #

    I am buying a home with central air and a heat pump. it is three bedrooms and i am converting a family room into the fourth bedroom we need on the first floor. The issue is when I put up the wall I will be closing off the heating and air source. Can I cut into the duct in the roof/floor between the first and second floor? If so can you show me a blow by blow demo on that?

    • Bob Jackson April 20, 2010 at 7:15 pm #

      Hi Nick,
      Without know more details about your ductwork, vents and floorplan, it’s difficult to give a definitive answer. The surest solution is to tap into the main trunk and run a new line as I’ve shown in the article.

      > Can I cut into the duct in the roof/floor between the first and second floor?
      > If so can you show me a blow by blow demo on that?
      If I understand your situation, the ductwork for the family room is between the ceiling/floor of the 1st and 2nd levels of the home. This would make it expensive and messy to tear out the ceiling drywall to install new ductwork; I don’t have a demo for this.

      You might consider a different approach – running new a supply duct down from the attic, hopefully through a closet on the 2nd floor, to the 1st floor family room.

      I think your situation is challenging enough to seek on an on-site assessment/estimate by a professional HVAC technician. Check Kudzu.com for professionals in your area.

      Thanks for reading,
      Bob

  12. Peter January 4, 2011 at 5:43 pm #

    I wonder if just redistributing the insulation might have gone a long way to fixing this problem, without adding the second duct. I think I would have given that a try first.

    Also, where you advise having someone hold a vacuum cleaner to catch the falling dust as you cut the hole in the drywall, I’ve found that fine dust quickly destroys vacuum cleaner motor bearings. They still work, but become unbearably noisy. I use an old one for jobs like that.

    • Bob Jackson January 4, 2011 at 6:08 pm #

      Improper insulation was a definitely contributing factor, however when I compared the air flow to my daughter’s room at the end of that long run of duct to the other bedrooms by holding my hand next to the ceiling vent, the air flow was significantly less strong. That bedroom above the also garage receives a lot of sun loading from the east and south roof faces. In the summer, the garage gets very hot from outdoor temperatures in the 90’s F to low 100’s F plus the heat from the car engines which doesn’t help.

      I grabbed the house vacuum cleaner for small jobs like this. I use the yellow shop-vac for real messes and big jobs. Thanks for the tip!

  13. Glenn June 15, 2011 at 4:08 pm #

    I’ve got a persisting problem with my computer room upstairs, esp. being too hot in summer. The attic AC/HT unit sits between the upstairs bedrooms (3). Theo BR on my side of house is the coldest room in house and the BR next to it is functioning very well. I’ve partically closed the other 2 BR vents and opened my BR (home office) all the way and it makes no difference. They’re still cold and I’m still hot.
    The AC service we have says the connection of the main return does not allow room to replace with a connector that allows 2 returns. My thought is to place a small return, the size of AC vents and ducts, right above the computers in the ceiling and run that return duct into the duct work of the main return just a couple of feet before it enters the unit.
    Does this sound reasonable solution? If so, can I just cut into the main duct and tape and AC putty the smaller duct into it – making sure it seals good? Or is there a “T” connection to allow the main large return to flow unimpeded and a entry for smaller duct to fit into the side?
    What may help to know is that the AC/H unit has no room to move or add any larger attachments due to how the attic is built, BUT there is room to install a small return vent and its duct work to run into the main return.

    Advice is greatly appreciated!
    Glenn

    • Bob Jackson June 15, 2011 at 5:55 pm #

      Instead an AC return duct, have you thought about installing a new fresh air supply duct and vent? This will be much more effective compared to an air return duct. How is the office bedroom temperature when you leave the door open? Leaving the door open is about the same as installing a new return duct.

      You’ve already tried to balance the AC by closing vents/registers in the other bedrooms. What’s needed is more cold supply air to make the office bedroom comfortable. Is there something in the system layout that prevents running a new fresh air duct to the ceiling? A couple of photos of the attic air handler and ductwork would help. You can send pics to me at this address: bob (at sign) handymanhowto.com.

  14. Becky June 21, 2011 at 2:14 pm #

    Hi, I have a similar project we are working on: We have an upstairs that does not have any ventilation what so ever. Plenty of windows, but no venting to push heat or cool air from the central unit (in basement) into the upstairs. Need to know how to go about getting this done to make this into the kids’ room. We do have three openings that lead into the attic, looks like the same as your pics posted, with the joists and insulation all over the place (although ours looks like old newspapers, should we replace?). We are unsure how to get started with this: where to put the vents, how many vents…
    Thanks!

    • Bob Jackson June 21, 2011 at 9:31 pm #

      The first thing to do is verify your AC unit can handle the extra cooling load of the 2nd floor. See this central AC sizing chart for guidance. If your AC unit is too small to handle the 2nd floor living space, it’ll run all the time and you won’t be comfortable. My AC unit was properly sized to handle the total living area, so my problem was limited to improving the air supply.

      The other question is ductwork sizing, which is not a simple question that I can answer here because it requires specialized knowledge, room measurements, design and calculations. You might try this online Ductwork Design Service or better, hire a local HVAC company for an onsite assessment.

  15. daniel June 22, 2011 at 2:14 pm #

    Hi,

    I am finishing my basement and the contractor added a piece of wood to seal the space between the metal box (the vent) and the drywall.

    Should i be worried that the wood will get moldy due to the AC?

    thank you!

    • Bob Jackson June 23, 2011 at 1:25 pm #

      It’s normal to build a wood frame behind the drywall to mount the vent boot. The wood shouldn’t get moldy because as the air conditioner cools the air, the excess water vapor condenses on the evaporator coils inside the air handler and drains away… so you’ve got cool dry air blowing out the vent. This is a key purpose of air conditioning, to both cool and dry the air to lower the relative humidity.

  16. Blake August 1, 2011 at 1:56 pm #

    Hi Bob,

    I have a slab garden home with a storage room off the back inside the screened in patio. The storage room is insulated therefore I put a dog door in the door so my dog can go in and out to get out of the heat. All duct work is in the attic with vents in the ceiling. I would like to run a vent into that room to keep him cool during the hot summers. The master bathroom shares the wall with the storage room. I have two options. Tap into the vent that feeds into the masterbath and run at best five more feet to the storage room. OR Come off the main trunk which is at the front of the house in the attic and make a long run across the entire attic. The storage room is tiny and wont take much to cool but I am extremely concerned with messing up the balance of the rest of the house. What would your advice be?

    Regards,
    Blake

    • Bob Jackson August 1, 2011 at 5:22 pm #

      I normally don’t recommend splitting a branch line, but since it’s a “tiny” storage room go ahead and do it. Take care to install a ceiling register with adjustable louvers that will fully close. Open the louvers just enough to make the storage room comfortable and limit the impact on the master bathroom. During the winter, close the vent louvers if you don’t want to heat the storage room.

      Have you thought about a return air duct/vent? Otherwise the air will be forced outdoors around the dog door. If there’s an interior door to the storage room without a bottom weatherstrip or sweep, that could be your air return. (If it has a bottom weatherstrip/sweep, leave it alone.) Might need to shorten the door so there’s a 5/8″ clearance above the floor for the return air. Or you could install a pass-through vent in the common wall shared by the master bedroom and storage room; this might not be desirable though because the dog will hear you and bark and whine.

      Should splitting the branch line prove unsatisfactory, you can always run a 3″ duct line from the main trunk at the front of the house.

  17. scott November 9, 2011 at 2:41 pm #

    Bob, It appears that you used R6 flex. I am getting ready to replace all of my attic flex and was told that R8 had to be used in attics (any area without climate control) due to a code change. I was told that I would have to wrap or blow insulation over all R6. Please help.

    • Bob Jackson November 9, 2011 at 7:12 pm #

      Simply buy R8 rated duct. Home Depot has Master Flow 6 in. x 25 ft. Insulated Flexible Duct R8 Silver Jacket, Store SKU # 810991.

  18. paul November 16, 2011 at 11:18 pm #

    i added an extra duct but the air flow has stop where i tapped into and both have stop working any suggestions?

    • Bob Jackson November 17, 2011 at 5:30 am #

      I need the particulars of how to you installed the branch line. Did you tap into the rigid trunk ductwork or wyed into a flexible line? Are you sure you tapped into an air supply line and not an air return line? Pictures will help a great deal – send them to bob (at) handymanhowto.com.

  19. dan March 28, 2012 at 2:35 pm #

    Thanks – very nicely done.

    GAF web link has changed to: http://www.gaf.com/Other-Building-Products/Ductwork/Ductwork.aspx

    Dan

  20. bill clagget November 24, 2012 at 12:16 pm #

    is a 12 inch duct too big for a standard room

    • Bob Jackson November 25, 2012 at 1:00 pm #

      Hi Bill,
      The short answer is “Yes – a 12 inch duct is probably too large for a standard size room.’, but determining the correct duct size requires some thought and engineering as discussed in my reply dated June 21, 2011 at 9:31 pm in the comments section of this project. Also see my discussion of AC Sizing in the comment dated December 14, 2011 at 11:00 am in this related project.

      Let’s assume a ‘standard size room’ is 150 square feet. According to “How Contractors Really Size Air Conditioning Systems” the typical cubic feet per minute (CFM) of airflow required is 1.04 CFM/square foot. You will therefore need at least 156 CFM of airflow and possibly more (1.5 CFM/square foot = 225 CFM) if the room is not well insulated or you live in a very hot or cold climate.

      Let’s assume 1.04 CFM will be sufficient air flow. Plugging the following values into the ResDuct™ – Residential Air Duct Calculator:
      * Duct Type for Supply & Return: Flexible
      * Airflow CFM for Supply & Return: 156

      Results in a 9 inch diameter flexible duct.

      Re-running the Air Duct Calculator with 1.5 CFM/square foot for 225 CFM total airflow estimates the flexible duct size at 10 inches in diameter.

      Please run the duct size calculator with actual square footage and duct type (sheet metal, fiber board, flexible) for your room to get a more accurate estimate.

      If in doubt, you could install a 10 inch diameter duct with a louvered vent to regulate and better balance the airflow.

  21. Tony N January 23, 2013 at 9:44 pm #

    am i able to cut a hole in my air duct in my basement to heat and keep a section of my water pipes warm when the temp drops well below freezing

    • BobJackson January 24, 2013 at 7:43 pm #

      You want to install a new air vent in the main trunk line to keep the basement water pipes from freezing? If you have a rigid board or sheet metal trunk line, a Speedi-Collar with built-in damper to regular the air flow should do well. It’s fast and easy to install. The damper has a rachet system to lock it in place and closes air tight when you don’t need it in warmer weather.

      If the exterior basement walls aren’t insulated, then insulating the walls will minimize heat loss and cold intrusion.

      I also recommend wrapping the water pipes with foam pipe insulation if you haven’t done that already. Foam pipe insulation is available at home improvement stores.

  22. John Keenan February 27, 2013 at 6:56 pm #

    I want to remove a duct from the main supply trunk and move it back, but there is another branch in the bay I want to use. Can I run the two vents out of the same tap on the supply trunk, using a wye branch?

    • BobJackson February 27, 2013 at 8:21 pm #

      The best way would be disconnect the old branch line and cap off the trunk tap, then install a new starting collar at the bay trunk line for the new branch line.

      I’m guessing there’s no room to install a starting collar on the bay trunk line? What size is the branch line that you want to relocate? In the follow example, less assume it’s a 6 inch branch line.

      1. Cap off the old 6 inch branch duct at the main supply trunk starting collar. Remove the old starting collar and install a cap plate.
      2. Remove the 6 inch starting collar at bay trunk line that you want to wye.
      3. Install a new starting collar that is 2 inches larger in diameter on the bay trunk line. In this example, the new starting collar is 8 inches in diameter.
      4. Install an 8 inch inlet to 6 inch outlet wye at the bay trunk line. You may need to run a short section of 8 inch duct to connect the 8 inch starting collar to the 8 inch wye inlet.
      5. Connect the old and new 6 inch bay branch lines to the wye.
      6. Install louvered air registers in the rooms to balance the air flow.

      The reason for an 8 inch inlet on the reducing wye with two 6 inch outlets is to provide sufficient air volume for the two branch lines. An 8 inch duct has 201 square inches of area. A 6 inch duct has 113 sq. in. of area. 201/113*100% = 178%, meaning the 8 inch wye inlet has 78% greater capacity than the 6 inch wye outlets. This is should be enough to make the rooms comfortable assuming no special heating or cooling needs, for example, a room with lot’s of windows and sun exposure. In my home, most of the louvered vent registers are about 2/3rds open, therefore I have more than sufficient HVAC capacity.

      If you believe an 8 inch to 6 inch wye won’t be large enough, use a 10 inch inlet wye with 6 inch outlets. A 10 inch duct has 277% greater capacity (314 sq. in.) compared to a 6 inch duct.

      Summmary:
      * Best method is to install a new starting collar in the trunk duct for the relocated bay branch line.
      * If that’s not possible, start with an 8 in to 6 in reducing wye.
      * Should the 8 in wye not be sufficient, you can always cut a larger hole in the trunk line for a 10 in wye.

      The risk of installing too large a wye is your vent registers could get noisy from too much air flow whistling past the louvers.

  23. Daniel March 2, 2013 at 11:13 pm #

    Hi,
    I am finishing/soundproofing a studio/music room over garage and it will be sealed as airtight as humanly possible. I thought I should install a return vent so we don’t choke on our own CO2. I would install an a/c vent as well but don’t think the system can handle it. Will this help?

    Also, and I can’t seem to find this out anywhere, how do you cut a start collar hole in flexible duct? The room is unfinished and the large return air trunk is right there. I would like to tap into it. (Much easier than trying to thread a new duct back to the main unit). Are there special take-off collars for flex? How do I cut a neat hole with that wire running through it?

    Thanks!!

    • BobJackson March 3, 2013 at 11:13 am #

      > I would install an a/c vent as well but don’t think the system can handle it. Will this help?
      A return air vent without a fresh air supply vent will not have much, if any, affect on the rate of air exchange in the room over the garage.

      > I can’t seem to find this out anywhere, how do you cut a start collar hole in flexible duct?
      > Are there special take-off collars for flex? How do I cut a neat hole with that wire running through it?
      Starting collars are for rigid duct board and sheet metal ducts. An air duct wye connector is used to tap into flexible duct. The wye is installed by cutting flex duct in two, slide the two ends on the wye and seal with HVAC tape and a zip tie. Connect the new branch duct to the 3rd leg of the wye the same way.

      Take care to correctly orient the wye. For a fresh air supply line, the air flows in the bottom and out the top of the Y in a diverging path. With a return air duct, the air enters the top of the Y and exits the bottom in a converging path.

  24. John Keenan March 24, 2013 at 11:24 am #

    I should have gotten back to you sooner. I closed off the one branch. I put in an 8″ whye on the top of the main trunk where I wanted to relocate the branch. That location had a branch line already. Then I fed off in two directions. I reduced the branches to 6″. Damper in each(wasn’t a need for them, but they’re there). Worked out great. Thank you. Due to previous renovations I assume, someone found it easier to run flex tube across bays in basement when changing heat register locations, than to change location on the main trunk allowing to run in the bay. I hated having flex tube hanging all over, not to mention that I eliminated over 10 ft of supply. I was just concerned that running two branches off one location on the main trunk would be a problem. It wasn’t, as far as I can tell.

    • BobJackson March 24, 2013 at 12:21 pm #

      You’re welcome! Thanks for the update.

  25. Anita May 31, 2013 at 2:59 am #

    My heating and cooling runs straight through my basement ceiling but there is no air flow or vent in my basement to keep from moisture building up. So I want to add a vent along it. I also have my Husband helping, what should we do?

    • BobJackson May 31, 2013 at 9:17 am #

      My finished basement shares the same trunk ductwork with the 1st floor of my home. This project shows how to install a new air vent in the basement suspended drywall ceiling.

      Let me know if you have more questions.

  26. Joe Schaerer July 3, 2013 at 1:55 pm #

    Will this Speedi-Boot from Home Depot work just as well installing a new register in the floor. All my bedrooms have two register except the one in the front of the house which seems to get very warm in the summer. The vents are all in a line so finding the main ducting shouldn’t be a problem. I live in a re-manufactured home and everything is accessible under the unit.

    • BobJackson July 3, 2013 at 6:56 pm #

      Speedi-Boot is great for floor installations. Consider using a 90-degree register vent model which is often needed to avoid a sharp bend in the flexible duct connection.

      References:
      Floor Vent Installation Methods YouTube video

      Speedi-Boot Installation Instructions on page 8:
      Floor Installations
      There are four pre-piloted holes in the four corners of the Speedi-Boot to fasten to the bottom of the floor decking with sheet metal or wood screws. You may also use the trim register pilot holes and the hanger arms to secure to the floor decking. This creates a tight fit and compresses the rubber gasket to the floor deck eliminating air leakage. The hole in the floor decking must be cut 3/8″ larger than the outer mud-ring dimension.

  27. Rick Hester July 20, 2013 at 6:11 am #

    I have a one story home in NC with HVAC ductwork running in the crawl space. We have recently converted a screen porch to a sun room and want to install vents in the sunroom to provide HVAC. However, the floor is poured concrete covered with tile. I asked our HVAC technician about the capacity of our unit and says that it is large enough to handle the extra square footage. When I asked if he could run a vent through the ceiling, he stated that air doesn’t like to “flow up hill.” He had no suggestions for a solution.

    Do you have any suggestions on getting cool/warm air to flow from the main trunk under the house, up over an eight foot ceiling, and out into our sunroom? The total length of the duct from main trunk to outlet would be about 30-35 feet.

    The sunroom is only 12 X 15, so would I need two ceiling ducts?

    Thanks for you time.

    • BobJackson July 22, 2013 at 12:49 pm #

      The 8 feet ceiling height isn’t an issue, the 30 to 35 feet of total duct length and guessing two 90 degree bends will have significant friction losses. 6 inch duct would normally be sufficient for a 12 x 15 room, but due to the long duct length install a duct booster fan or use 8 inch duct without a booster fan.

      Two ceiling ducts will be needed (supply & return ducts), especially if you plan to close the door between the sun room and house which would block the door air return. Use louvered vent registers to balance the air flow and shutoff the air when you’re not using the room to save on heating/cooling costs.

  28. Ashley October 24, 2013 at 8:35 am #

    We bought a home and there is a vent in the master bedroom but its not connected to any duct work (there is no heat or air). Everything is ran under our house though. Would it be a big deal to tap into the main line and go ahead and run it? Is it a difficult task?

    • BobJackson October 24, 2013 at 5:53 pm #

      > vent in the master bedroom but its not connected to any duct work
      Very odd! Is the attic above the master bedroom? Is there any ductwork in the attic? I’d be concerned there’s a disconnected duct somewhere in the attic.

      Is the master bedroom on the first or second floor? Where is the air handler located?

      Installing ductwork is mainly an issue of figuring out the best path from the trunk duct to the new vent given the layout of your home. For example, if you have a single story home with ductwork in the crawl space it would be easiest to install a branch duct to a vent in the bedroom floor.

  29. Ashley October 29, 2013 at 8:57 am #

    Ok, I’m sorry. I should have given you a bit more info. The house had been foreclosed on when we bought it and it was very apparent that the first owner was in the middle of reconstructing it. There were a lot of “loose ends”, unfinished rooms and such. There’s no “attic” as the roof on the second floor are the A ceilings? So the duct work starts right under the master bedroom (which is on the first floor) and runs throughout the house from there. So I was thinking just tapping into the mainline right under our bedroom. I mean it’s obvious he just didn’t finish it because all the pipe that’s needed is already under the house. :) thanks.

    • BobJackson October 29, 2013 at 6:50 pm #

      The home was being remodeled by the prior owner before foreclosure interrupted the job, leaving you with significant unfinished work. There’s no attic because the home has cathedral ceilings. The trunk duct runs below the main floor.

      A new branch duct can be installed from the trunk to the new vent in the bedroom. Are there existing supply and return vents in the bedroom? What are the dimensions of the vents and ducts? How large is the master bedroom – width and length? What is the distance from the trunk duct to new bedroom vent? Do you have a ceiling fan? Is there a crawlspace or basement? Is the trunk duct made of sheet metal, rigid ductboard or flexible duct?

      > it’s obvious he just didn’t finish it because all the pipe that’s needed is already under the house.
      Given the incomplete ductwork, I recommend inspecting all the ductwork for:
      * Open ductwork – a huge energy waste
      * Separated ductwork, broken seams, air leaks

      This Ductwork Guide will be helpful to understand your HVAC system and proper ductwork installation practices.

  30. bob November 1, 2013 at 11:21 am #

    Hey Bo..I also have a basement. They installed a new Trane system a few years back. They gave me one duct off the main trunk in what was then the finished side. They said they’d come back and add a few more ducts and a return when I completed finishing the basement.

    We just about have the remaining 12 x 18 section finished. Had the guy back out. He said he’d add as many ducts as I wanted but it likely would not warm the basement….same old story, stat upstairs etc etc. He suggested I could add a single duct in the 12 x 18 area and a return…all for some air flow but I should also add some electric radiators.

    After reading this thread I think I could handle the job myself. I am a bit concerned about the house needing to be rebalanced though. The tech did not seem to be. Thoughts???

    Anyway…the main duct and a return runs against the long (back) side of the room. Should I just pop a vent thru the drywall into the duct for the vent or should I bring the duct line off the trunk to the room center…or does it matter….or maybe adding the vent accomplishes nothing! Thoughts????

    Similarly, what do I do about the return…right off the trunk for the return or run something the center of the room. How much space should there be between the vent and the return? Again it’s a 12 x 18 room and the main duct / main return runn along the long back wall.

    Thanks Bob!

    • BobJackson November 2, 2013 at 12:32 pm #

      > He suggested I could add a single duct in the 12 x 18 area and a return…
      > all for some air flow but I should also add some electric radiators.
      I agree with the HVAC technician’s assessment. Basements tend to be cooler than the main house. Because the thermostat is upstairs, there’s no way to signal for heating without installing a remote temperature sensor in the basement, which would make the main floors too warm. An electric radiator is easiest.

      > After reading this thread I think I could handle the job myself. I am a bit
      > concerned about the house needing to be rebalanced though. The tech did not
      > seem to be.
      I concur with the tech.

      I was talking to my local building inspector recently and he said a building permit with a load calculation (a complex engineering task best left to the pros) is called for when adding new ductwork. I think most people would think that excessive for minor branch line additions but I’m not going to argue with regulations. Do install a louvered supply vent register so you can adjust the room airflow. Return vents must be the fixed permanently open type (non-louvered).

      > the main duct and a return runs against the long (back) side of the room.
      > Should I just pop a vent thru the drywall into the duct for the vent or
      > should I bring the duct line off the trunk to the room center
      The supply and return branch lines must be installed with a start collar, duct, vent boot and register. Ideally, place the supply vent at the far side of the room away from the door and locate the return a couple of feet away from the door. If the basement room has windows, the supply vent should near the windows. If access limits the placement, separate the two vents as much as possible so the air fully mixes in the room.

      Also see my advice dated December 14, 2011 at 11:00 am in the comments section of this post.

      Thanks,
      Bob

  31. bob November 2, 2013 at 2:53 pm #

    Thanks Bob. I don’t see a Dec 2011 post but i will look again. As far as a permit to install a duct….that officially crosses the line into ‘in it for the $$$$’. What safety issue could there be with an unbalanced house? Jeez.

    So in your opinion is it even worth adding a vent and return..or just add the radiators…or both.

    BTW, the vent would be towards the end on the trunk. At the the is already a vent going upstairs. Would adding this vent for basement a feet away from an existing one matter?

    • BobJackson November 2, 2013 at 6:00 pm #

      > I don’t see a Dec 2011 post but i will look again.
      Scroll down about 4/5ths of that web page. Comments are listed in chronological order.

      > So in your opinion is it even worth adding a vent and return…
      > or just add the radiators… or both.
      Definitely add the supply and return ducts for year round humidity and temperature control. The electric radiator is portable can be used as needed, but it won’t do anything for fresh air exchange.

      If you have several people in the finished basement room addition without air vents, you’ll quickly notice it’s getting stuffy (humidity is going up) due to lack of fresh air exchange. I have a similar issue with my basement bedroom… it only has a supply air duct and no air return – an error by previous homeowner’s who hired a contractor to finish the basement without a building permit. Close the door, there’s no air exchange and it gets stuffy. I’ll install either a return duct or jump duct soon.

      > BTW, the vent would be towards the end on the trunk. At the the is already a vent going
      > upstairs. Would adding this vent for basement a feet away from an existing one matter?
      It will matter, the question is “how much”? It depends on the size and length of the trunk duct, new branch line, etc. That’s why a louvered supply vent is recommended to balance the air flow by trial & error until all rooms are comfortable. One or two louver adjustments is usually sufficient.

  32. bob November 4, 2013 at 3:05 pm #

    ok, The return will work well as its right at the opening to this area. The vent will be a about 12 feet away from the return, in the back of the room. My only issue is that I can see how I can craft a collar to go thru the drywall and into the trunk and affix a say 14 x 6 louvered grill to it.

    I can also see atttaching a collar and some insulated duct and attaching that to a speedy vent but…. I have a dropped ceiling and this becomes problematic. Should I attempt to find a way to get the vent in the center of the room, again 12 foot wide room, vent would be 6 feet from wall…or just hang it off the trunk which already petrudes about 2 feet into the room. I hope this makes sense.

    • BobJackson November 4, 2013 at 8:51 pm #

      Is your dropped ceiling drywall or removable acoustic panels? Speedi-Boot is compatible with both. If your suspended basement ceiling is drywall like mine, then physical access and vent placement is limited.

      > or just hang it off the trunk which already petrudes about 2 feet into
      > the room. I hope this makes sense.
      The supply air trunk duct is exposed inside the room? Is it rigid duct board, sheet metal or flexible duct? Pictures would help – send to bob (at) handymanhowto.com

  33. Bob November 5, 2013 at 9:37 am #

    >Is your dropped ceiling drywall or removable acoustic panels? Speedi-Boot is compatible with both. If your suspended basement ceiling is drywall like mine, then physical access and vent placement is limited.

    Armstrong Ceiling Panels. I do not recall why I had an issue on the other side of the basement. I recall purchasing a speedy boot and returning it for a round 8″ vent with diffuser…it may have something to do with the location or a tight fit.

    > or just hang it off the trunk which already petrudes about 2 feet into
    The supply air trunk duct is exposed inside the room? Is it rigid duct board, sheet metal or flexible duct?

    I could not get a picture that covered the whole area. The basement ‘L’ shaped. Down the stairs is the main area, finished and about 27 x 27…but has a 10 x 12 work room in the back corner. There is on supply line in this area over a sitting area.

    The area in question is being finished..its almost done. It’s a 12 x 18 area that sort of completed the’L’. The air handler sits between these two areas. Ridged 12 x 12 (?) silver covered duct flows from the air handler to this area. It runs about 15 into the 12 x 18 room. Similar sized return duct runs in back of the supply and abuts the back wall. I can not tell what area(s) above feed the return. I was able to see that the supply feeds two vents in my family room above..one at about each end of the room. If its feed something else, I can not tell but it could be; perhaps not. My vent being added to the basement would sit at the far end this supply/return run, a foot from one supply deed the room above and 2 feet from the physical end of the run.

    The supply is positioned for easy access. The duct is faced with a 12 x 12 already painted board but the bottom is still exposed. I can easily fashion a collar thru the board into the ridgid ductboard and affix a 14 x 6 (?) louvered vent. As mentioned, the bottom is still exposed, so I can get in there and in sure a tight seal around my makeshift collar.

    It seems less work to me to install in this fashion and would sit 2 foor from the back wall…but if moving the vent essentially another 4 foot into the room and having it blow down rather than out makes a difference I am up for it I guess. Wheeew! I appreciate your patience and expertise!

    The neighbor question doing the whole thing…he noted the door at the top of the stairs is cut an inch from the floor and acts as a return pulling air from the basement upstairs…not to mention the doggie door that is there as well!

    • BobJackson November 5, 2013 at 7:02 pm #

      > I can easily fashion a collar thru the board into the ridgid ductboard and affix a
      > 14 x 6 (?) louvered vent. As mentioned, the bottom is still exposed, so I can get in there
      > and in sure a tight seal around my makeshift collar.
      I believe that is the best plan.

      > he noted the door at the top of the stairs is cut an inch from the floor and
      > acts as a return pulling air from the basement upstairs
      A 1 inch gap along the door bottom wouldn’t provide area for return air from the 12ft x 18ft finished basement. Most doggie doors are weighted or have a magnet to keep it closed blocking the return air path. A return vent and duct in the basement will pressure balance the room (air flow in = air flow out) and be the most comfortable solution. You might try a transfer grill over the basement stairway door – this works only if there are no closed doors in the finished basement.

  34. bob November 8, 2013 at 10:52 pm #

    Well, I went down to measure before buying any product to install my vent. Good thing. The way the rigid duct hangs from the rafters and after dropping my ceiling will only allow me to get a 4″ high vent thru the side. The good news is they sell a 3.25 x 10 starter collar that would make the job simple but….is that opening adequate?

    The alternative is to go through the top of the rigid duct and use flex duct to bring the sucker to away from the wall dropping down into a ceiling tile. More cost, more work AND I would have to be in the rafter bay right along side and existing supply run…I was planning on staying a few feet away from the existing supply run and coming out the side. I can’t really mover over…there is wiring above the rigid duct in all other bays.

    is a 3X10 opening sufficient? Heck, I am not even sure they sell louvered grills that size….

    • BobJackson November 9, 2013 at 12:11 pm #

      If I follow your description correctly, the square or rectangular air duct is made of duct board and runs between the floor joints. There’s only 4 inches vertical clearance between acoustic tile suspended basement ceiling and the floor joists. The finished basement room is 12 feet x 18 feet.

      A 12ft x 18ft room is 216 square feet. At 1 CFM of air flow per square foot of floor space you’ll need 216 CFM from the vent. Selecting fiber board supply duct and 216 CFM airflow in the ResDuct™ – Residential Air Duct Calculator results in a 9 inch diameter air duct.

      9 inch diameter round duct is not a common size. 8in and 10in diameter duct, start collars and boots are available in a wide range of configurations. Because it’s a basement with minimal exposure to the weather and your ceiling workspace is limited, let’s choose an 8 inch duct diameter.

      A critical constraint is the duct pipe and vent boot must fit the 4 inch vertical clearance between the ceiling tiles and floor joists.

      This configuration may work for you:
      * Speedi-Boot 4in x 12x Wall Stack SBH-4128 WS
      * Speedi-Products 8in Oval to Round Straight Boot SM-OTRS 08
      * 8 inch round duct board start collar

      The SBH-4128 WS is only 3.5 inches high to fit between the ceiling tiles and floor joints.

      Install the start collar in the side of the duct board trunk, attach the oval to round adapter so the offset end runs below the joist, then Speedi-Boot wall stack vent. Fasten the sheet metal duct connections with at least 3 screws, seal the joint with mastic (best) or metal foil HVAC tape and wrap it with duct insulation.

      I couldn’t find the dimensions of the SM-OTRS 08 oval, but you can contact the manufacturer to verify the oval-to-round adapter fits the Speedi-Boot wall stack.

      Let me know if this approach works for you.

  35. bob November 9, 2013 at 5:23 pm #

    No, How did you get those pictures in there? The supply and return trunk / ducts run under the rafters perpendicular to them and against the back wall creating a bulkhead. A wire runs above the trunk through the rafters up until the last two rafter bays below. The end rafter bay contains the duct running upstairs. The next rafter bay in is where I could add another supply through the top but then I’d have two supplys right next to each other.

    I can come out the side anywhere but the trunk only hangs so low and fatoring in the dropped ceiling leaves me with only 3 – 4 of vertical space for a grill….though it can be a wide grille. The room is 12 x 18 and opens the lager space. I wish I could post a picture if told how I will…

    I could get a collar thru the top, flex duct to that and use a speedy duct to my ceiling tile….assuming my grid falls in the right spot when I put it up. But it seems having two supplies side by side is not a good thing.

    • BobJackson November 10, 2013 at 10:17 am #

      > I can come out the side anywhere but the trunk only hangs so low and fatoring in the dropped
      > ceiling leaves me with only 3 – 4 of vertical space for a grill….though it can be a wide grille.
      I’m getting a better idea of the duct and joist layout, but not quite understanding the 3-4 inches of vertical space constraint if the trunk duct hangs below the joists. It seems there should be adequate clearance to run a collar, flex duct and vent boot between the rafter bays?

      > I wish I could post a picture if told how I will…
      You can email photos bob (at) handymanhowto.com, replace the (at) with the @ symbol with no white spaces, or upload photos to a photo sharing website like Flickr and paste the link.

      > I could get a collar thru the top, flex duct to that and use a speedy duct
      > to my ceiling tile… assuming my grid falls in the right spot when I put it up.
      > But it seems having two supplies side by side is not a good thing.
      If you can some out anywhere along the trunk duct then a start collar in the side is better because it avoids an extra 90 degree turn.

      I look forward to the photos.

      Thanks,
      Bob

  36. bob November 11, 2013 at 11:24 am #

    I’ll try to upload tonight. I measured. The trunk is 9″high. It abuts the rafters…or put another way, hangs 9″ below the rafters. My ceiling tiles will come about 4 inches from the rafters. That means I have about 5 inches of trunk left to tap into …from the side……and part of that is thickness of the bottom f the trunk.

  37. bob November 23, 2013 at 2:45 pm #

    I am back…trying to post some pics:
    This is from the rear back corner of the 12 x 18 room..

    basement air ducts

  38. bob November 23, 2013 at 2:46 pm #

    …if that works…I’ll post some more!

    • BobJackson November 23, 2013 at 5:11 pm #

      Yes – I see the photos.

      The single link to the photobucket album will do. Just post the remaining pics to the album and give each one a title like “Basement Ductwork 1″, “Basement Ductwork 2″, etc. to identify it by name in our discussions.

      Thanks,
      Bob

  39. bob November 23, 2013 at 6:14 pm #

    Here is looking towards the 12 x 18 room, you walk past the washer / dryer to get there. The Air handler is in back of the sliding door ..

    [URL=http://s753.photobucket.com/user/rfuschjr/media/p0.jpg.html][IMG]http://i753.photobucket.com/albums/xx179/rfuschjr/p0.jpg[/IMG][/URL]

    The first image showed the boxed in duct work…here is a shot looking up at it.

    If this works Ill describe my issue again un a latter post

  40. bob November 23, 2013 at 8:20 pm #

    Well, I hope the 3 or so pics made it, One shows the main room looking into the 12 x 18 area in question. Another shows the bulk head covering the existing duct. The one photo shows the supply and return alongside each other…the return stops and the supply continues to about 3 feet from the back wall. At the end of this run is a branchoff going up stairs. I want to put a vent for the basement in this area. I could go out the top but I’d have to runs tapping off the supply duct alongside each other. I really just wanted to come out the side with a vent. I can only get something 3 to 4 inches tall through the side though since the supply duct sits up against the rafters and my dropped ceiling has to drop down 4 inches. Will something 4 x 10 or so be ok?

    • BobJackson November 25, 2013 at 4:07 pm #

      Your basement ductwork photos cleared up the situation.

      The supply and return air ducts are made of fiberglass duct board concealed by an interior soffit. Because there’s only ~3 inch of clearance between the soffit fascia board and the duct board it would be difficult and unsightly to cut into the soffit and bring a branch duct out the side of the duct board trunk. A duct board start collar (or takeoff) is too long and will extend past the soffit.

      The supply duct extends past the hallway into the 12ft by 18ft room in the finished basement.

      My recommendations for installing the new branch air ducts are:
      * Install the return air duct in the center of the hallway (blue line in photo at the previous link).
      * Install the supply air branch duct at the 2nd to last floor joist bay (red line in photo).
      * Extend the supply air duct as far as possible into the 12x18ft room to maximize the air circulation. (The length of my red line was limited by the picture.)
      * Both branch air ducts will be run from the top of the trunk duct board via flexible duct to a Speedi-Boot mounted between the floor joists. Not sure if mounting to the floor joists would be too high for your acoustic tile ceiling. If the ceiling tiles are strong enough, let the boot rest on the tile and use the register vent screws to pull the boot snug against the back of the tile. Otherwise you could install blocks extending past the floor joist edge to mount the Speedi-Boot lower to match the ceiling tile.

      It would be best if you can find a No. 320 Top Takeoff for Duct Board to tap into the duct board trunks. The Top Takeoff will fit better in the floor joist bay and be more efficient compared to a standard round / straight start collar. It will also avoid a possible constriction in the flexible duct with a 90 degree bend. A similar Top Takeoff for duct board is the Heating & Cooling Products 298 EZ Turn Ductboard Take-Off.

      Check with your local HVAC supply stores (where the pro’s shop) to find a duct board top takeoff collar because it’s a specialty item and I doubt the big box home improvement stores will have it. Take care to buy a takeoff collar for fiberglass duct board because there are many similar styles of takeoff collars with mounting tabs (fingers) but those are designed for connecting to sheet metal duct.

      Please post pictures of the finished branch ducts to photobucket. I’d enjoy seeing how it turns out.

      Thanks,
      Bob

  41. bob November 25, 2013 at 6:54 pm #

    Very clear now but note I would have no problem getting a 4 x 10 through the side…the interior soffit comes down enough it would not look bad…not sure if that makes a big difference.

    The start collar you describe is at my local Lowes. I had any issue on the finished section of my basemet with a speedy duct and getting it to fit and ended up using a 6 or 8 inch round thing with insulated duct connected right to it…it has a louver too..was a pain to put up but I think the way everything lined up with the ceiling tile square I could not squeeze in a boot.

    My only concern with having the retur where you say (not that there is any where else to put it is that it is by the washer…I wonder if laundry smell / dtergent smell or noise will permiate up thru the house?

    Note the pic you labelled 12 x 18 room…the one looking into the unfinished part of the basement I am working on. My hvac is behind the 2′ sliding door you see.Ther are actually two 2′ doors there…you only see one. Originally the hvak sales guy said to wall that in and put a large return there. The installer said it was better not to box the unit in…the idea being that no one knows how big the next unit would be and isntalltion might be a pain if walled in. I could still add a larger return their..the doors are an inch or two off the floor…its not a tight seal..but I am still by the laundry area and just to the right of the hvac is the stair way comng down and under it are some pets in cages! I am afraid that smell might permiate thru the house..that would be worse than the dtergent smell!

    Maybe I can load a few more pics.

    • BobJackson November 25, 2013 at 7:44 pm #

      > I would have no problem getting a 4 x 10 through the side
      Do you mean the side (cut a hole in the soffit fascia board) or the bottom where the duct board is exposed in the photos? Placing a return vent at the end of the return trunk inside the new room would get you away from the clothes washer and pet cages. The supply vent should be located at the far side of the room such that the air flow circulates the full length of the room.

      > The start collar you describe is at my local Lowes.
      Ah yes! Standex Air Distribution Products, Inc. sold at Lowes is the same manufacturer for the Snappy top takeoff start collar. I checked the Lowes.com website and only saw the T7 takeoff which is for sheet metal duct. I’m sure your store has the duct board takeoff or similar product.

      I’m not understanding the problem fitting a Speedi-Boot. A photo of the other vent boot with the insulated connector would help. The important thing is you’ve got a solution.

  42. bob November 26, 2013 at 10:09 am #

    1) thru the side….meaning horizontally thru the white board that boxes in the duct board….just pop a lovered 4 x 10 vent right onto the white board.

    2) As I recall the ceiling grid in the other portion of the basement fell in the middle of a rafter making it difficult to get the speedy boot to fit. I was able to get the flex hose around it and had enough for to afix a 6″ round vent.

    • BobJackson November 26, 2013 at 11:12 am #

      > just pop a lovered 4 x 10 vent right onto the white board
      I couldn’t think of a good way to install a start collar in the side of the duct board through the soffit fascia. The problems I see are:
      * A round start collar would be too long to extend beyond the white board fascia. Tin snips will solve that.
      * The hole in the fascia board would have to be sawn to fit the wide flange of the start collar through, leaving a large gap.

      A register box might work with modifications. The box is 3.5 inches high which appears to be more than the space between the duct board trunk and the front of fascia board. Let’s assume the No. 505R or other slim profile register box will fit. The advantage is the rectangular box flanges are mounted at the front so you don’t need to cut an oversize hole in the white fascia board as would be for a round start collar. The disadvantage is the register box is designed for connecting to flex duct or sheet metal duct. It can be modified to function as a duct board start collar by:
      * Cut the rectangular hole in the white fascia board.
      * Insert the register box and mark the circular duct outline against the duct board.
      * Cut the circular hole in the duct board.
      * Insert the register box fully into the fascia and duct board.
      * Reach through the register box and mark the exterior round metal duct where it meets the interior duct board. You’ll be working blind by feel but the duct board interior face will guide your marker.
      * Cut the duct board mounting fingers / tabs with tin snips to the depth of the marked line on the outside of the round metal duct.

      Now you can insert the register box, reach inside and bend the duct board mounting finger against the duct board to hold it in place. Seal the joint with mastic or HVAC metal foil tape. The register box body may conceal the round duct joint against the duct board making it impossible to seal the joint. Since this is a return air duct inside the home’s thermal envelope (air conditioned space), an air leak here isn’t a real concern.

      Another method for creating a return air duct between the soffit fascia and duct board trunk would be to fabricate a rectangular box out of fiberglass duct board. A 4″ x 10″ return duct box can cut from a single strip of 28″ long duct board that’s 3- or 4 inches wide measured fit exactly in the rectangular hole from the face of the soffit board into the trunk duct. Use a serrated knife to miter the interior corners at 45 degrees like V so the duct board corners will fold a 90 degree angle. Fold it into a rectangle and tape the single corner joint closed. Fasten the short jump duct to the trunk duct with HVAC tape. The return vent register can be mounted to the white fascia board with screws. Now that I’ve written up this idea, I like this option the best – inexpensive and simple.

      > As I recall the ceiling grid in the other portion of the basement fell in the middle of a rafter making it difficult to get the speedy boot to fit.
      Make sense. It looks like a Speedi-Boot supply vent should fit between the 2×10 or 2×12 joist bays.

  43. bob November 26, 2013 at 12:24 pm #

    I may still go the ‘thru the top route’ if there is an advantage…. but my proposed ‘through the side’ route would use this starting collar from HD:

    http://www.homedepot.com/p/Master-Flow-3-1-4-in-x-10-in-Rectangular-Stack-Duct-Starting-Collar-SCF3-25X10/100139382

    1) cut the hole through the white board.
    2) Mark and cut the duct
    3) Slide the starting collar thru the side board and into the duct and flip the little flanges 90 degrees insuring the collar cant pull out. Tape around the duct…I can get my hands in there.
    4) I will now have some of the starting collar sticking out thru my white board..I’d have to trim that and add a grill whose louvers would fit inside the collar. so I could control air flow.
    5) Repeat on the ‘return’ end but using a non louvered return grill.

    I end up with 4 x 10 or so grills blowing out….as opposed to 6 x 12 blowing down I guess…not sure the impact of that….

    Feasable..any downside?

    • BobJackson November 26, 2013 at 8:44 pm #

      I think “through the top” would be less work and a better installation because it avoids sawing the white fascia board and would use a top take off for duct board.

      My concerns about the Master Flow Rectangular Stack Duct Start Collar are:
      * Although the product descriptions says “Use to transition from ductboard plenums” the tabs/fingers appear to be too short to make a 90 degree bend against the interior face of the duct board. Your duct board trunk is probably 1 inch thick. Best to measure the two and confirm… I could be wrong. Most duct board start collars either have extra long mounting tabs and/or a straight neck to fit through the duct board so the base of the tabs extend slightly past the inside face of the duct board (compare to the tabs for the top takeoff at the above link). I checked my local Home Depot but they didn’t stock that Master Flow 4×10 Start Collar. Lowes had similar wall stack take-off with maybe 1 inch tabs that aren’t long enough to bend back against the duct board… forcing the tabs would just crush the duct board.

      * Duct fittings must be mechanically fastened via metal tabs (e.g. start collars), draw bands, screws or clamps. HVAC metal foil tape shouldn’t be considered mechanical fastener because it’s really just a sealant. I don’t doubt the rectangular start collar flange could be successfully held in place with several layers of HVAC foil tape but the tape can fail over time and wouldn’t be up to Code.

      * You’d need to saw the rectangular hole in the fascia board large enough to fit the base flanges through. Not a big deal but may require a larger register vent to cover the hole.

      Supply and Return Air Vent Placement:
      The essential issue isn’t how you make the new duct work connections, rather where the new vents are located: Were the supply and return vents located along the interior soffit, the airflow will tend to “short circuit” and flow between the two vents resulting in poor circulation at the far end of the room.

      The return vent should be located near the room entrance or close by in the hallway which is OK because the room does not have a door.

      The supply vent should be placed at the far end of the new room to avoid dead zones and maximize the air flow. The concept is illustrated in Figure 28-2 on page 2 of Ductwork. Also see Are your ducts placed properly? by Kelly’s Heating and Air Conditioning.

      Hope this helps.

  44. bob November 29, 2013 at 1:47 am #

    through the top it is…thanks!

  45. Ed February 2, 2014 at 11:18 am #

    Hi, Bob.
    Is it legal to have a heat vent/register in the middle of the floor? I’m removing a wall between the kitchen and the dining room and I would have to install a flat register covering if I leave the heat vent where it is. People would be walking over the register. Is that okay as long as it doesn’t bother me aesthetically?

    Thanks,
    -Ed

    • Bob Jackson February 2, 2014 at 8:46 pm #

      Hi Ed,
      I would relocate the floor register to an out of the way location close to an exterior wall and away from the return vents for better circulation. Keep in mind that if you sell the house a floor register in the middle of the room will raise questions.

      I’m not aware of any Code requirements that says you can’t have a floor register in an odd location. The 2012 International Mechanical Code upon which local Building Codes are based states:

      603.18 Registers, grilles and diffusers.
      Duct registers, grilles and diffusers shall be installed in accordance with the manufacturer’s installation instructions. Volume dampers or other means of supply air adjustment shall be provided in the branch ducts or at each individual duct register, grille or diffuser. Each volume damper or other means of supply air adjustment used in balancing shall be provided with access.

      603.18.1 Floor registers.
      Floor registers shall resist, without structural failure, a 200-pound (90.8 kg) concentrated load on a 2-inch-diameter (51 mm) disc applied to the most critical area of the exposed face.

      Best to call your Building Dept. and ask if there’s anything in the local Building Codes that would prohibit the register in your proposed location.

      Since people would be walking over the floor register, consider using a vent filter to keep dirt out of the duct:

      Let me know what your local Building Dept. says.

      Thanks,
      Bob

  46. Owen April 15, 2014 at 1:14 pm #

    Hi Bob,

    I bought a home in North Idaho last year that included a detached shop- about 30×40. It has 16 ft ceilings and above that is a 1000 sq ft apartment.

    The apartment is heated by an 80% efficient propane fired furnace that is in the attic. The hot water heater (propane) is in a closet in the apartment also. Other propane appliances are the stove in the apt, and a “hot dawg” ceiling mounted furnace in the shop.

    I’ve been going through (what feels like) an inordinate amount of propane. My theory is there are 3 major problems 1) Not quite enough insulation in the attic 2) since the furnace is in the attic (and not in the heating “envelope”) it has to work harder to get the air warm and therefore uses more propane and 3) the hot dawg must run in very cold weather to keep the water pipes (located in an interior wall of the shop) from freezing.

    I am contemplating what it would take to retrofit the apartment- and put the heating registers at the base of the interior walls- and run the duct work on the ceiling of the shop. There is a bathroom at the back end, and I was thinking I would put the furnace right on top of that.

    Is this a crazy plan? I’m just wondering if it sounds feasible, and wondering how much it would actually reduce my propane usage.

    I’m really interested in what you think.

    Thanks,

    Owen

    • Bob Jackson April 15, 2014 at 9:45 pm #

      Hi Owen,
      Nice setup! I like your detached workshop!

      > My theory is there are 3 major problems
      > 1) Not quite enough insulation in the attic
      Proper insulation would be the #1 priority for minimizing heating losses. See the ENERGY STAR Recommended Levels of Insulation R-Value map to determine how much additional insulation is needed.

      Northern Idaho is located in Zone 6 on the map which calls for attics to have R49 to R60 insulation.

      Now that you know the recommend insulation R-Value, the Owens Corning Insulation Calculator will estimate the amount of additional insulation needed for batts/rolls and blown loosefill insulation in a Northern Idaho 838xx zip code. Guessing your attic already has 6 inches of insulation the additional insulation needed for a 1200 sq. ft (= 30 ft x 40 ft) is 16 inches of batt insulation for a recommended 60 R-Value total.

      > 2) since the furnace is in the attic (and not in the heating “envelope”)
      > it has to work harder to get the air warm and therefore uses more propane
      My air handler with a natural gas furnace is also in the attic. Yes, it’s not the ideal location but common for the reason you cited. The most important improvement here is fixing any duct work problems and R-8 rated duct insulation.

      You should also crawl around the attic and seal all electrical wiring and plumbing penetrations in the walls and ceiling with something like GREAT STUFF joint and crack minimally expanding foam. It’s available at the hardware store in an aerosol can. Caulk around the bathroom exhaust fan, too.

      Take care to leave an air gap around recessed lighting fixtures that generate a lot of heat.

      Check your electrical wall outlets for air leaks and install a foam gasket (available at the hardware stores) behind the cover plate because the outlet box may not have insulation behind it or has compressed the insulation to the point it’s lost most of it’s insulation effectiveness.

      > Is this a crazy plan?
      It’s a very reasonable plan… something I would do. If the walls are insulated, I’d start with the attic as that may be sufficient.

      > wondering how much it would actually reduce my propane usage
      See the ENERGY STAR Estimating the Payback Period of Additional Insulation article which has a fairly simple formula for calculating the Years to Payback.

      Let me know what you do and the results.

      Thanks,
      Bob

  47. Jeff July 11, 2014 at 9:33 pm #

    Hi Bob, great walkthrough on this, however I would caution your readers on cutting through the OSB blind valley, depending on their local code.

    In California especially, the blind valleys often are actually shear walls and used to stiffen the structure for wind and earthquake loads. Cutting through them in most cases is against code, and even if it is within code, you have to keep it below a specified percentage of area of the panel, and you need to radius the cuts. Unfortunately the only way to do something like that is to put an access hatch in the ceiling on the other side of the blind valley/shear wall.

    • Bob Jackson July 12, 2014 at 5:03 pm #

      Hi Jeff,
      Thank you for pointing out the shear wall issue and differences in local Building Codes.

      I live in the Atlanta, GA area which has very little seismic activity of any significance and inexpensive earthquake insurance. My home is therefore (and unfortunately) not subject to the more stringent Building Codes like California (earthquakes) and Florida (hurricanes). I remember the reinforced trusses, walls and straps at my former South Florida home.

      As always, the homeowner should consult your local Authority Having Jurisdiction (AHJ) – a.k.a. city or county Building Dept – for guidance.

      Thanks,
      Bob

  48. Randy July 21, 2014 at 9:24 pm #

    Hi Bob,

    Hoping you can help. I am tearing down a wall that separates two bedrooms, in order to make a large master bedroom. The wall I am tearing down has a return duct in it. Can i cap off this return duct and not use it? I will still have one return duct that will be approximately in the middle of the new larger room.

    the measurement of the rooms are 15 x 11 and 11 x 11. The larger room has the one return duct and two floor registers. The smaller room has one return duct that I want to remove since its in the wall I will be tearing down and it also has one floor register. Thanks for any advice.

    Randy

    • Bob Jackson July 22, 2014 at 7:18 pm #

      Well, it depends on knowing the sizes of the supply ducts, return ducts and vent grilles.

      The easy way is to temporarily cap off the return duct during the remodeling phase and see if the room is getting enough air with the doors closed, but I doubt that will be satisfactory because “return openings will need to be 2 to 3 times the size of the supply duct depending on system design velocities” – reference page 153, Return Air Flow Considerations. The reason return ducts need to be larger than supply ducts is the supply ducts have higher pressure and air velocity, whereas return ducts are lower pressure and velocity.

      If the room is not comfortable with a single return vent you’ll need to convert the existing wall return vent into a ceiling or floor return depending on if the return duct enters wall from above or below.

      BTW – take care that you’re tearing down a non-load bearing wall.

  49. Mattie_K October 13, 2014 at 12:52 pm #

    Hi Bob, I’m stumped! I’ve got the vent boot installed, worked out great! However, the other end where I would connect the new branch line to the existing system doesn’t have the rigid duct board where I can cut it out and install it. Instead, It looks to be a round insulation wrapped trunk line, looks similar to the branch lines, however is around 2x to 3x bigger around. With it being round, it doesn’t appear that the starting collar would fit like it should. Is there a different type connector that I should be using? I don’t believe it’s flexible duct either, could it possibly be rigid duct board wrapped in insulation? Thanks.

    PIC: http://imgur.com/7mB0Yn7

    • Bob Jackson October 13, 2014 at 6:28 pm #

      Hi Mattie,
      It appears from your photo the trunk duct is round sheet metal. A 90 degree saddle tee take off is needed to connect the new flexible duct branch line to the round sheet metal trunk duct. See this annotated version of your photo.

      Examples of 90 degree saddle tees are:

      and this more basic item at Home Depot.

      Do not install a sheet metal Wye saddle because your other branch duct connections are 90 degree connections and a Wye will imbalance the air flow. The air flow will tend to follow the Wye branch because it has to turn less versus the four other 90 degree take offs.

      The steps to install the saddle tee take off are:
      1 – Measure the diameter of the round sheet metal trunk duct and the flexible duct branch line. Measure only the duct itself, do not include the insulation wrap.
      2 – Buy a 90 degree saddle tee take off that matches the trunk duct and flexible duct diameters.
      3 – Hold the saddle tee against the trunk duct insulation jacket where it will be installed (e.g. the side like the other branch duct connections) and trace the round circle inside the take off.
      4 – Cut a hole in the insulation jacket following the traced circle for the takeoff.
      5 – Now slice a vertical slit long enough that you can pull apart the sheet metal trunk duct insulation jacket and slip in the flanges of the saddle tee.
      6 – Slide the saddle tee flanges under the insulation jacket and position it so the 90 degree tee is horizontal. Now trace inside the take off on the sheet metal duct.
      7 – Use tin snips to cut the hole for the take off in the sheet metal trunk duct. Tip: Drill a 1/2 inch starter hole inside the traced circle to get the tin snips started.
      8 – If the saddle tee has a self-stick sealing gasket like the Speedi-Products item at Amazon.com, press it against the sheet metal trunk duct and fasten the flanges with sheet metal screws. Otherwise, you’ll need to seal it with mastic – which is always recommended.
      9 – Pull the insulation wrap over the saddle fitting and seal with HVAC tape and optionally mastic.
      10 – Connect the flexible duct branch line to the saddle tee.

      Thanks,
      Bob

  50. Mattie_K October 26, 2014 at 6:42 pm #

    Wow, thanks for the prompt reply Bob. it took me a while to find one of the 90 degree saddle tee’s, no Lowes or Home Depot within 30 miles of my house had one. I ended up ordering on Amazon. I must say, your write up worked like a charm. Thanks a million times over for helping out with this!

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