Fireplace bumpout / doghouse leaks air


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Old 01-21-14, 06:31 AM
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Fireplace bumpout / doghouse leaks air

I've got a 13 year old home with a direct vent fireplace housed in a bump-out (or doghouse or whatever phrase you prefer) off the back of the family room, faces West. All winter long, air just streams in around the fireplace housing (between the metal of the fireplace housing and the brick facade, and out of the top and bottom air vents). I've caulked all of the outside seams to no avail.

It occurred to me when watching a Holmes that the soffit is vented, but there's no matching roof vent. So air comes in the soffit and has no place to go. Except my family room.

Options are to seal off the soffit on the bump, or add some sort of roof vent to the bump to give the air someplace to vent, or tear off all the cladding and siding and roofing and do it all over. And even if I do any of those, I have no idea of how well (or even if) the inside of the bump has insulation / vapor barrier (I have one bale of Roxul left from the basement finishing that I could use).

Biggest question - does this small an "attic" need the same level of venting as, say, a home attic (where I have a ridge vent)? Would it be OK to just seal off the soffit vents?

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Patrick
 
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Old 01-21-14, 07:30 AM
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I don't think the problem is the soffit venting. It's that the air is having access to your fireplace unit where it can make it's way to the room. Providing another vent in the attic or "exit" does nothing to seal up the open path to your living space.

Properly constructed that bump out should be like the other walls of your home with insulation, vapor barrier and air gaps sealed. Is your fireplace an insert that can be removed or do you have any easy access into the bump out space? Unfortunately I think it's something easy to build properly up front but difficult to fix later as a repair. Have you tried sealing around your insert to block the drafts? That should help alot as I assume your gas fireplace is direct vent and gets it's combustion air from outside.
 
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Old 01-21-14, 07:33 PM
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Blow it up and start over, I guess...

I've tried caulking around the insert, and in extreme weather, I've sealed it with Tuck Tape, rigid foam boards, and even just used plastic over the whole thing. And I agree the whole thing is just badly built, because there's no evidence of any air sealing anywhere.

There is no easy answer. I'll have to demo it from the inside either way, to get proper insulation and vapor barrier (or spray foam). I was hoping for a relatively easier answer, since we haven't used the fireplace at all in the past five years because when it's cold enough to use it, there's too much cold air streaming in to the room.

But there's no conceivable reason to have the soffit venting there if there's no where for the air to go, right?

Oh, and thanks for the reply.
 
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Old 01-22-14, 04:58 AM
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There is no reason that needed vented soffit.
 
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Old 01-22-14, 06:38 AM
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It looks like your house is vinyl sided. You could remove the siding starting at the top and work down. Cut an access hole in the exterior sheeting and you can see inside and work to fix the problem. Then put sheeting back over the hole and re-install your siding and the repair will not be visible and no mess inside your home.
 
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Old 01-22-14, 06:44 AM
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What is under the bump? Is it insulated and sealed with foam, then covered with plywood?
 
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Old 01-22-14, 05:59 PM
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If it's like the rest of the house, it's paper-faced batt insulation, $8/truckload stuff, one staple per 8 board feet, inside flakeboard sheathing (also $8/truckload stuff), maybe (50/50 chance) covered with house wrap, but I never saw one inch of tape on any seams.

Real low quality for everything. But on the 50% chance that there is actually wrap on the outside, I think most of the air is leaking in through the soffit. I think when it warms up I'll pull some of it and stick a camera in there and peek around.

I was mainly interested in whether I needed to be concerned about rot or mold if I seal up the soffit vent and maybe even the whole soffit. If I use the fireplace, even though it's direct vent, I'm still wondering if the inside of the bump is going to heat and cool, maybe causing condensation.
 
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Old 01-22-14, 06:33 PM
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That's an option, except for putting a vapor barrier very effectively on the inside of the insulation.

I'll throw your suggestion in the pile come Spring. Thanks!
 
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Old 01-23-14, 02:42 PM
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Just because the soffit material is vented does not mean that the area itself is vented. For that small of an area, the siders probably used what material they had on hand, which would be vented in most cases. I would look more toward the fact that you have a double walled exhaust vent that both exhausts hot gas and brings in fresh air for combustion. There may be a seal issue and normal convection is causing air to enter. Your vent looks very low so it is almost directly straight out the back. The bump out also is fairly shallow, so curious how the insert would be hooked up. What is the make and model of the fireplace?
 
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Old 01-23-14, 04:29 PM
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I had somebody look at the vent, and he didn't find any issue, but that was a cursory look at just the outside. So your suggestion is also a possibility. I have the whole thing hermetically sealed on the inside, so I can't give you the make/model for a few days until the weather gets back to non-Arctic and I can take all the insulation off.

Thanks for the feedback.
 
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Old 10-03-14, 09:31 PM
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Did you ever figure this out? I have the same situation. Fireplace guy came out and said he thought it was really weird that there were soffit vents in the doghouse and to seal them up. Said it wouldn't have affect on moisture or cause mold since it's effectively part of the interior of the house. But I'm wondering what others have done.
 
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Old 11-09-14, 11:23 AM
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OK, I finally got a ladder tall enough to get up there, and pulled the trim pieces so I could get access to the soffit from the side. Not surprisingly, there were two completely open vents, and no insulation or any blocking to keep cold air from the North/West from roaring into the fireplace and leaking out through all the seams around the fireplace, even after I caulked the heck out of everything.

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After picture (4" Roxul cut to fit):
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I did put a 2x4 across the top to hold it down in the fiercest winds, but I don't think there'll be much trouble because it was cut to fit snugly. I ran it the whole length, not just on top of the two perforated panels.

Hurrah! We can use the fireplace again!
 

Last edited by YodaTheMedic; 11-09-14 at 11:25 AM. Reason: Adding things I forgot.
 

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