Comments on: How to Add a Room Air Duct for Heating & Cooling – Part 1

By: Bob Jackson

Bob Jackson — Thu, 17 Nov 2011 10:30:46 +0000

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.

By: paul

paul — Thu, 17 Nov 2011 04:18:23 +0000

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

By: Bob Jackson

Bob Jackson — Thu, 10 Nov 2011 00:12:14 +0000

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

By: scott

scott — Wed, 09 Nov 2011 19:41:38 +0000

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.

By: Bob Jackson

Bob Jackson — Mon, 01 Aug 2011 22:22:14 +0000

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.

By: Blake

Blake — Mon, 01 Aug 2011 18:56:05 +0000

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

By: Bob Jackson

Bob Jackson — Thu, 23 Jun 2011 18:25:31 +0000

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.

By: daniel

daniel — Wed, 22 Jun 2011 19:14:05 +0000

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!

By: Bob Jackson

Bob Jackson — Wed, 22 Jun 2011 02:31:30 +0000

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.

By: Becky

Becky — Tue, 21 Jun 2011 19:14:31 +0000

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!