How to Fix a Leaky Gas Flue Roof Vent – Part 2

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How to Fix a Leaky Gas Flue Roof Vent – RTV sealant is applied to the storm collar to fix the roof leak. This repair is continued from How to Fix a Leaky Gas Flue Roof Vent – Part 1.

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.

Type B Gas Vent – Flashing Cone and Storm Collar

Fix the Type B Gas Flue Vent 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

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.

Old Flue Vent Caulk 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

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

Reseal 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

The Flue Vent 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.

Type B Vent Pipe Rust under Rain Cap

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.

Replace the Roof Flue Vents

Due to the corrosion and the rain water leak still not being fixed, I decided to replace the roof vents. See How to Fix a Leaky Gas Flue Roof Vent – Part 3 for details.

Thanks for reading,

Bob Jackson

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  1. Mark October 8, 2014 at 9:03 pm - Reply

    I hate to tell you, but silcone sealant will NOT adhere to a metal surfaces like this. It would have leaked at that seam too within a month or less after a couple of hot and cold cycles with the gas heat running and hot and cold days and nights. You would need to use a flexible roofing sealant that comes in a caulk tube.

    • Bob Jackson October 9, 2014 at 5:50 pm - Reply

      Hi Mark,
      I called the Rutland Fire Clay Company to confirm the 500°F RTV High Heat Silicone Sealant is appropriate for Type B gas flue vents. Rutland confirmed it is a suitable sealant for this application. I also requested a product data sheet which states: “For interior or exterior use” and “Surface Prep: Surface must be clean, dry and free of dirt, oil, grease and rust.”

      When I had the entire flue vent assembly replaced, the second HVAC repair company used ADASEAL HVAC/R SILICONE SEALANT. The ADASEAL product specifications state: “Exterior / Interior Use” and TYPICAL USES: HVAC/R exterior and interior, outdoor vents, pipe openings, electrical penetrations, glass, clean metal, non-oily woods, painted and plastic surfaces, and refrigerator gaskets.”

      The silicone sealant did not leak for 2-1/2 years. I’m sure it would have lasted longer but I had the roof replaced after a hail storm. The roofer used a MasterSeal/Sonolastic NP 1 polyurethane sealant on that job and might be the other type of sealant you’re thinking about. I notice the silicone sealants are rated to 400F or 500F whereas the NP1 polyurethane sealant is only rated to 180F. I don’t know how hot the exhaust gases are at the roof line.

      Either way, the silicone and polyurethane sealants have not leaked.

      I therefore find no merit in your claim the high temperature exterior rated silicone sealants will leak if applied per the manufacturer’s instructions – clean and rust free surfaces, etc.


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