The HVAC contractor began the work by disconnecting the old vent pipe at the first joint below the roof deck in the attic. To disconnect the pipe, just slide the retaining collar up and wiggle/lift the pipe to separate. The shiny new pipe sections are shown in this photo.

Furnace Vent Pipe in the Attic

Roof Vent Demolition

With one man working in the attic, the other HVAC technician went to the roof top to disassemble the vents. He began by lifting the retaining collar and wiggling off the top section of vent pipe. The top section with the rain cap is laying to the right in the photo below.

The storm collar is removed by cutting the caulk line with a utility knife and wiggling the collar up the pipe. Once clear of the flashing cone, the storm collar was cut in two with tin snips and pulled free of the vent pipe. Cutting the collar was quicker than working it off the length of the pipe.

Removing the Storm Collar from the Old Vent Pipe

After removing the storm collar, the caulk line at the flashing cone is cut and the old pipe is pulled down into the attic. The retaining collar at the bottom of the vent pipe inside the attic will not fit through the flashing cone, so the pipe must be pulled down.

The second vent stack is removed by the same procedure.

New Roof Gas Vent Installation

Flashing Cones

We originally planned to remove the old flashing cones. The HVAC technician advised against it, explaining the cone was in good shape and he was concerned about the shingles being brittle in the cool (mid-40′s) December weather. We agreed to leave the flashing cones in place.

The old caulk is trimmed and peeled away from the neck of the flashing cone with a utility knife. A clean bare metal surface is needed for a water tight caulk line.

Cleaning Up the Flashing Cone Neck

Flashing cone after cleaning the old caulk from the neck.

Roof Vent Flashing Cone Cleaned and Ready for New Pipe

The second man inside the attic pushes up the new section of vent pipe through the flashing cone. The man in the attic then attaches the vent pipe existing lower section inside the attic.

Pushing Up New Type B Vent Pipe

The joint between the vent pipe and flashing cone is caulked with Adaseal HVAC/R 100% RTV silicone high temperature caulk.

Caulking the Vent Pipe at the Flashing Cone

The storm collar is installed by sliding it over the pipe and down to the flashing cone. The storm collar is sealed with a generous bead of silicone and smoothed (radiused) with a finger.

Caulking the Storm Collar

The rain cap simply slides onto the vent pipe. The technician secured the rain cap with a short 1/4″ sheet metal screw to ensure it doesn’t blow off in a very strong wind. The screw is optional and must not penetrate inner section of the double wall pipe.

Installing the Rain Cap on the Roof Vent Pipe

The vertical seam on the flashing cone was caulked with silicone and the vent stacks are spray painted black for appearance. The two vent stacks are also now equal height for a better appearance.

New Gas Vent Stacks

Inspection of the Rusted Vent Stacks

The old vent stacks were saved for inspection to see if there was an obvious source of the rain water leak. The black RTV sealant beneath the rain cap and on the storm collars is only one week old and did not stop the leak. The vents are a bit dented having been dropped off the roof onto the lawn.

Old Type B Gas Vents

The rust hasn’t corroded through the pipe wall, but the rust lines indicate rain water getting inside the pipe.

Rain Cap and Vent Pipe Rust

It’s really hard to say if this was the leak source, or maybe water was getting inside the vertical seam and channel past the storm collar.

Rusted Vent Pipe

No Leaks!

The new Type B roof vents were installed only a day before a new cold front brought steady rain. The vents are water tight and no water trails are to be seen on the shiny new sections of pipe in the attic.

The job took about 2 hours and the final cost was $350 versus the $400 original quote because we decided not install new flashing cones.

Hope this helps,

Bob Jackson

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The right vent stack in this photo continues to have a slow leak only when it rains. Resealing the storm collar didn’t fix the leak. I learned after the roofer resealed the vent stacks there was severe rusting under the rain cap that couldn’t be seen from the ground. It’s also possible rain water was following the vertical seam down the pipe and getting inside. Given the extent of the corrosion, I decided the best option was to completely replace the vent stacks.

Type B Gas Furnace Roof Vents - Still Leaking

The rusted vent pipe beneath the rain cap was unusual for galvanized pipe and could be a letting in rainwater.

Rusted Vent Pipe at the Rain Cap

Bids to Replace the Roof Vent Stacks

I obtained several proposals to replace the vent stacks from highly rated Heating and Air companies on Kudzu.com. The minor issue was finding HVAC contractors that also did roof work. The bids were in the $400 to $600 range to replace the vent pipe starting at the first joint in the attic and all exterior roof components: vent pipe, flashing cone and rain cap. I chose the low bidder, which included a written 100% satisfaction and 1 year guarantee in addition to be highly rated on Kudzu.com. The company manager double checked the 4″ diameter vent pipe was properly sized to ensure condensation wasn’t an issue and a 2-man crew came out the next day.

New Type B Roof Vent Materials

The 2-man crew arrived on time the next afternoon with complete inventory of Hart & Cooley, Inc. Type B gas vent pipe and roof flashings. The double-wall vent pipe is made in various lengths that snaps together.

New Hart & Cooley, Inc. Type B Vent Pipe

Hart & Cooley 4RWH Rain Cap – top view:

Hart & Cooley 4RWH Type B Gas Vent (Rain Cap)

Bottom view of the same. The function of rain cap is to vent the combustion gases, help prevent back drafts, keep out rain and discourage birds from nesting in the flue vent. The HVAC technician said the H&C product works well. Were a bird to build a nest, it will block the vent and a safety switch in the furnace will sense the back pressure and shut off the furnace.

Hart & Cooley 4RWH Type B Gas Vent (Rain Cap)

The HVAC contractor used the Adaseal International, Inc. HVAC/R silicone caulk to seal the vent flashings. It’s 100% silicone rubber rated for 450°F.

Adaseal HVAC/R Silicone Caulk

This repair is continued in Part 4.

Thanks for reading,

Bob Jackson

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The attic leak is believed to be caused by a bad seal around the storm collar. The storm collar acts like an umbrella to prevent moisture from entering the joint where the flashing cone meets the vent pipe.

Fixing the Storm Collar Leak

The storm collar simply slides over the pipe. To raise the storm collar, the old sealant is scraped off. The storm collar is raised to remove any sealant below the collar and to inspect the flashing cone / vent pipe junction.

Resealing the Storm Collar - Type B Vent Pipe

The flashing cone was sealed to the vent pipe with metal foil HVAC tape. The metal tape looked to be in good condition, and after 10 years, appeared to be permanently fixed to the pipe. We therefore decided to leave the metal foil tape in place.

Removing the Old Sealant

I expected the old sealant would have to be scraped off the with a 5-in-1 tool. Much to our surprise, the old sealant around the storm collar fell away in a single long ribbon! This stuff wasn’t doing anything to prevent rain leaking in! The old sealant was very flexible – like a large rubber band – but lacked any and all adhesion to the metal collar and vent pipe.

Old Storm Collar Sealant - Exterior Side

The interior side of the old sealant (where it met the metal surfaces) was weathered in sections with clear signs of water/dirt stains. It’s obvious this wasn’t a water-tight seal.

Old Storm Collar Sealant - Interior Side

Resealing the Storm Collar

A bead of the Rutland 500°F RTV High Heat Silicone Sealant was applied just above the flashing cone, the storm collar slid down the pipe and back into the place, then a liberal amount of RTV sealant applied to the storm collar. The roofer in this photo is roped off with a safety harness around his waist and thighs. He’s also wearing Cougar Paws roofing boots.

Roofer Applying RTV Silicone Sealant to the Storm Collar

Roof vent with new RTV sealant on the storm collar.

Type B Roof Vent - New RTV Sealant on the Storm Collar

It Still Leaks!

The next time it rained the roof vent still leaked. The leak was no worse, but no better. The storm collar wasn’t the source of my leak.

The roofer said there was severe rusting at the rain cap that couldn’t be seen from the ground. This isn’t normal for galvanized pipe. The rust was significant for a 10 year old installation.

I e-mail this and other photos to a Hart & Cooley, Inc. representative explaining the leak and failed repair. The technician rain water could be getting inside the double-wall pipe, or water could be channeling down the vertical pipe seam. The best option is to replace the pipe and rain cap; the quick fix would be to apply silicone sealant to the vertical pipe seams. I opted for a total replacement.

Repair Cost

The total cost of this repair was the minimum $200 fee for a service call by the roofer. While the roofer was up there, I also had the other PVC pipe boot replaced that wasn’t done earlier in the year as a preventive measure.

Replacing the Roof Vents

Due to the corrosion and the rain water leak still not being fixed, I decided to replace the roof vents. See Part 3 for details.

Thanks for reading,

Bob Jackson

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Type B Gas Roof Vents

The two gas flue vents are located high on the roof as shown in the above photo.

Locating the Roof Vent Water Leak

The primary combustion products of natural gas are carbon dioxide and water vapor. The water vapor can sometimes condense inside the flue pipe, pool and cause a leak. This most often occurs when the vent pipe is incorrectly installed with either:

• Insufficient slope – the pipe is laid too close to the horizontal.
  I knew my problem was not caused by condensation buildup because it only leaked when it rained, even in warm weather when the gas furnace was off.
• The pipe is too large in diameter, causing the exhaust gases to move to slowly.
  Slow gas velocity means the pipe won’t heat up along the entire length and the water vapor will condense inside, pool and leak at a joint. When the furnace starts up, the pipe will be cold and there will be some initial condensation. However, a properly sized pipe will have sufficient gas velocity that the pipe will warm up, evaporate the initial condensation and the water vapor in the exhaust won’t condense until it hits the cool outside air. If in doubt, have an HVAC technician verify the pipe sizing for your system. The 4 inch diameter pipe on my system is correctly sized for the BTU loading. See this link for more information: Gas Vent Chimney Sizing & Application Guide by Hart & Cooley, Inc.

Of the two flue vents in the attic, only the pipe on the left in this photo leaked. Rain water would run down the outside of the pipe and drip off the elbow; maybe 1 drop per minute.

Looking up at the roof penetration, I could see a trickle of water down the side of the pipe when it rained. The water originated at the junction of the flashing cone and vent pipe. Fortunately, the leak was very slow and only wetted the insulation, not reaching the ceiling drywall.

A larger view reveals several evaporation trails from the rain water leak down the side of the flue pipe.

The gas vent stacks extend several feet (per building code requirements) above the roof. In addition to the rain water leak, it looks like I need to replace the rain cap and top section of vent pipe due to rust. I think it’d look better to paint these black, too. There’s nothing like a steep 10/12 pitch roof to get the circulation going!

The gas vent pipe and various fittings are manufactured by Hart & Cooley, Inc. of Grand Rapids, MI.

Common Causes of Roof Leaks around Gas Vent Pipes

There isn’t much structural support for the long and slender runs of gas vent pipe as you can see in the above photos. Wind loading causes the vent stacks to flex and possibly crack the sealant around the storm collar. The storm collar acts like an umbrella to prevent rain water from entering the metal-on-metal joint where the flashing cone meets the vent pipe.

Talking to several HVAC and Roofing companies, they said these gas vents can be a challenge due to the numerous metal joints. Leaks can occur at:

• The neck of the flashing cone where it meets the vent pipe. The storm collar is designed to protect this area.
• The rain cap if damaged or corroded.
• The vertical seam on the vent pipe or the flashing cone – only if corroded or compromised.
• At the junction between two vent pipes, especially if the pipe aren’t seated well or crooked.

The most likely places are the storm collar seal, vertical pipe and flashing seams and the rain cap.

Given the high steep roof, my regular HVAC guy wouldn’t take the job. He recommended that I find a HVAC contractor that does “new construction” or check with a roofer. The roofing companies I called were ready and willing to do the job, but cautioned that if I needed anything more than resealing the storm collar or roof flashing, I would need a licensed HVAC company. I felt confident the leak was coming in at the flashing cone / vent pipe junction and had the roofer do the repair. You can find reputable HVAC and Roofing contractors at Kudzu.com.

Type B Gas Vent Information

For more information on typical Type B natural gas vent installation, see page 17 of the Hart & Cooley catalog. The Hart & Cooley Type B installation instructions are a helpful for better general understanding of the topic. Always hire a licensed HVAC professional if you need to install or replace gas vent pipe systems. If done incorrectly, exhaust leaks can kill you or fill the attic with water vapor that will condense and cause numerous problems.

RTV High Temperature Silicone Sealant

Within the confines of this project – resealing the storm collar – the Hart &  Cooley Installation Instructions state on page 6:

The RS storm collar must be placed immediately above the roof flashing. The storm collar must be sealed with roof cement or RTV silicone to seal the joint between the storm collar and the vent pipe. The storm collar provides protection against the entrance of any moisture into the flashing.
(See Figure 12.)

I chose the Rutland 500°F RTV High Heat Silicone Sealant to reseal the storm collar. The Rutland product is a “tough rubbery adhesive seal and maintains its flexibility at 450°F continuously and 500°F intermittently” which is recommended for this type of application. A cartridge of Rutland RTV Sealant is available at Ace Hardware for about $10. The Rutland silicone is available in black and clear colors.

This repair is continued in Part 2.

Take care,

Bob Jackson

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