Wood Chimney Chase Insulation
ricker511
| Posted in Energy, Heating & Insulation on
I have a wood burning fireplace insert with a stuccoed wooden chase. The damper works fine, but I get wicked drafts coming through the gaps in the insert. The insert installation manual calls for insulation in the first floor section of the chase, which I don’t think was done. My neighbors have the same set up and they don’t have any problems.
Any suggestions on the best way to rectify this problem?
Thanks.
Replies
Can you describe the installation in more detail? Is there a draft stop above the insert, at or near the bottom of the chase? Is there a chimney cap on top of the chase that the flue pipe exits thru?
My thoughts exactly. Missing storm collar, maybe?View Image
Last similar installation I did has a chimney cap with a neck for the flue pipe to come thru. I had the tin man size the neck so that the pipe was tight, because that's where a downdraft can happen, be it cold air or CO. Storm collar on top of that. Down lower, a few feet above the fireplace, there's a firestop, a piece of 24ga galv that the flue pipe goes thru. It's not level, it's at a 10:12 pitch, so the hole thru it is an oval, and it's not as tight.
Bottom line, it's hard to get these things tight enough to prevent drafts, especially since you can't put insulation against the pipe.
FYI I believe there are insulations that are approved for that kind of thing. I'm not positive, but I think rockwool is OK. Plus fire caulking to seal the gaps and imperfections of the sheetmetal work.
Instructions with the ductwork said nothing touches it except other metal parts of the system.
hmm ... I'm not an expert in fire blocks/stops. But I've always talked like it is OK to use fire caulking around sheet metal. If the instructions say nothing, I have to assume nothing is what they got their U-L rating with and ONLY nothing. Which seems a bit irresponsible (that is a strong word, that I don't intend in the negative sense) on the part of a manufacturer to design something that can't be installed in a reasonable manner (from an energy standpoint).
I'd get an opinion from the building official and also call the manufacturer's tech rep and discuss such a situation to see if there is something that can be done that is safe AND energy efficient. Interesting stuff.
If tearing into the chase is not an option and no access from e.g. the attic ... maybe make darn sure the chase is sealed all the way around ... especially at the top/around the flue and at the bottom (if it is exposed). If the attic has or can have access ... you'd want to seal around the flue. The builiding official can tell you what is safe ... combination of a sheet metal color, fire caulking, and the appropriate insulation.
There's no access to the chase and I don't mind cutting an access hole if insulating the chase helps. The damper is garbage, but even when I seal it with insulation, drafts through the unit are unbearable. The vent for the firebox is a possible culprit as well. Its on the windy side of the chase and I suspect if the damper was garbage the seal on the vent is no better. If it didn't cost so much I rip the whole thing out and put in a Rumford fireplace.Thanks for your help.
did they install a flue liner to reduce flue size when they installed the insert into your fireplace?
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I see everybody else is responding as tho this were a zero-clearance fireplace unit, not a fireplace insert.. Which is it? The answer to your problem may vary according to what the situation is.
An insert is a draft controlled wood stove essentially that is inserted into a masonry fireplace.
But your description of a wood framed chase with stucco outside makes it sound more like a built in zero-clearance.
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good point ...
Its a zero clearance fireplace unit. Majestic was the manufacturer. The chase is completely outside of the exterior wall with no access from the attic. I'm tempted to cut out an access hole in the back to get a look inside. The damper is a piece of sheet metal, not cast iron, but even when I block that up and close the outside air vent all you feel is cold air coming through. I was thinking of putting a top damper on but can't find any that fit. Most fireplace shops I've talked to have no interest in installing one (southern Chester County, PA). I just really wondered if inulating the chase would cut down on drafts coming through unit. I'm hoping the top damper takes care of the can lid damper the unit came with.Thanks for your help.
It sounds like you have two problems.One is the triplewall chimney. It is designed to pull cool outside air down the outer chamber and then back up the inner next to the flue interior. It is INTENDED to circulate cold air there. Modifying it could cause you dangerous consequences. There is nothing that an upper damper will do to change this. It is designed to work that way for safety when you are burning wood. But it sounds like you have this more for decoration than for burning.
It is possible that there could be a bad connection on this triplewall though adding to the problem. The joints should each be secured with three sheet metal screws. some installers don't bother with that and then later tradesmen lile sheetrockers or electricians can knock something loose.the other prob you may have is that the ext walls of the surrounding chase should be insulated but may not have been. This would cause the spillage of cold air from the unit itself.I would cut a hole in the wall large enough for my body to get in above the face of the unit. From there you can check on the chimney pipe sections and joints, use a firecaulk on the bottom joint if need be, and get in to use fibreglas to insulate the chase walls.Then once done, patch and paint the wall, or make a raised panel trim face to hide the hole
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