Air sealing and insulating direct vent gas fireplace termination
Hello all,
What has everyone done and/or used to air seal and insulate a direct vent gas fireplace?
At this stage of the design I can terminate on the roof or wall, is there a certain method that is preferred? I am leaning towards wall termination for two reasons: 1) I live in snow country so keeping roof penetrations to a minimum is ideal with a metal roof. 2) My planned air barrier is a vapor control membrane attached to the bottom side of the trusses for the ceiling and the exterior sheathing for the walls. It seems like the it will be easier to air seal to sheathing than it will be to a thin delicate membrane.
If I go through a side wall, I’m seeing thimbles specified where there is not direct contact of the vent pipe and the thimble. I will be choosing a high efficiency model (>70% efficiency) and the termination will be at least 20′ of vent run from the fireplace. With these two factors, I assume the outer wall of the vent pipe will never be hot enough to cause a fire, but that’s just an assumption. The vent pipe that is specified in all the install manuals is a sheetmetal duct within a duct. Exhaust on the inside, intake on the outside. 6-8″ in diameter depending on the BTU output.
I have not seen high temp RTV not eventually fail so I’m not in love with that product. I also have 3″ exterior EPS foam insulation. I could buy a sheet of rockwool for that area and get it closer to the vent pipe. Melting temp is 2150 °F for rockwool FYI.
Are there any brands or models of fireplaces that are high enough efficiency that they can use PVC vents like a modern furnace? That would make my life so much easier.
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By the way, this primarily a decorative/ambiance device. Primary heat source is ASHP. I'd prefer to stick to a gas fireplace since they output significantly more heat than an electric and it will be part of our backup heat source strategy for the super cold days or when the power goes out.
Looking at units like this: https://www.ortalheat.com/fireplaces/wilderness-front-44?hsLang=en
31,000 BTU, 80%
Working with the Ortal rep, I need a tape and/or sealant rated for 400 degrees. Anyone have a suggested product rated for this temp?
I found a caulking material at Lowes near the water heater section rated for 400 degrees. Used it to seal around the direct vent water heater dual vent, which is the same vent system you describe for the direct vent fireplace.
I found a caulking material at Lowes near the water heater section rated for 400 degrees. Used it to seal around the direct vent water heater dual vent, which is the same vent system you describe for the direct vent fireplace.
I'm interested to know more about this.
If the Ortal rep mentioned 400 degrees does that mean you can run the rockwool right up to the pipe? That would take care of the insulation.
And for the air sealing does one of the Lowes high temperature caulks work?
An update would be great. Thanks.
I've used RectorSeal HI-TEMP 100% RTV Silicone Caulk. It's very vinegar-y smelling and burns the eyes a bit in small enclosures. But seems to work great. There is higher rated caulking out there.
Most reps I talk to say NOT to put any insulation in contact with the pipe. I don't think it's a "rock wool" will catch on fire thing, but rather you're insulating the pipe which is already extremely hot from combustion.
I'd love to hear more on this as well, but that's just my experience.
If you want one, I think it is best to put it in the central area of the building and vent out the roof.
The wall vents work well if the unit is on an exterior wall often in a bump out. To my way of thinking everything is wrong this very common setup. The fireplace bump out are generally slapped together and leak air like crazy and rarely insulated most of the fireplace is made of steel so it sucks the heat out of the room when it is turner off.
The way I see it 20 feet of horizontal flu pipe is a big fire hazard and every install manual I looked at required several inches of clearance above a horizontal flu.
I get that you want to reduce the number of roof penetrations but I think the benefits of a short straight flu out weigh the small risk from a water leak.
Walta