how to seal leaky vent pipe in direct vent fireplace?

[Wester399]

Use some fiberglass batt..r20 or so because you cannot use the expanding foam for obv fire reasons.Just stuff it in the hole behind the plate that your exhaust pipe runs out.

[hearthman]

Wester, you cannot pack insulation or anything else into stated clearances. That wall firestop assembly was tested with an air space. You pack it and you can burn a house down. I've investigated enough of them to know.

[Wester399]

Sorry i didnt read the post 100 percent on the last install I did there was a 26ga steel box the venting went through before termination outside and we packed some extra space between that and the stud wall with insulation. Sounds like everyone here has suggested high temp silicone to seal it up.

[hearthman]

You have to read the mfrs listed instructions. Some of these firestops cannot be caulked on the inside and must breathe. Sealing and packing these firestops can be a fire hazard. Each model's instructions is the code.

HTH

[DarthDaver]

Use some fiberglass batt..r20 or so because you cannot use the expanding foam for obv fire reasons.Just stuff it in the hole behind the plate that your exhaust pipe runs out.

This is a good example of what not to do. The thimble is supposed to be an air gap for a reason, not an insulated space, regardless of the insulation used. A quick check of any manual (you know...those things that come with every piece of equipment but you've probably never read) or code book will tell you this. Insulating this space turns it into a fire hazard. Every time I installed a piece pf equipment that I had never seen before I always took the time to read the manual...it's always a good starting point for any proper installation.

[Kyoufu]

Well I'm not sure about resurrecting post's from the dead, but here's a summary of a white paper duravent did on exactly this issue which disagrees with some of the prevalent wisdom here.

https://mcusercontent.com/620b42dd9f...s_20201117.pdf

[hearthman]

Thanks for posting this. I will discuss it with the UL Standards Technical Panel and NFPA 211 technical cmte. In the meantime, note Duravent still covered themselves by pushing back to the ANSI Z21.88 listing agency. They claim minimal heat transfer. ANSI looks at overall temp rise and pyrolysis. This cavity would capture a lot of heat and has historically caused fires when packed with insulation. Note, they did not test assemblies that were properly caulked, nor did they address what operational cycles providing heat were needed to mitigate any attic condensation. They made a typo on the ASTM std for noncombustibles- it's E-136.