Fix direct vent FP draft from outside?

[Scottrichards]

I have searched through the forums, but I haven't really seen how to fix this problem after the fact. The builder who built my house went out of business and cannot help me. I have a Heatilator ND 4842IL Propane direct vent fireplace installed in a bump out/chase. I have always had a dramatic draft coming out the bottom of the fireplace when not in use. It was too the point I ended up just covering the whole fireplace over from the inside with plastic and not using it. You could see the plastic suck in and out from the draft on really cold and windy days.

Anyway, I am putting on an addition on the house and had the new different general contractor take a look at it and try to see if it was insulated. He took some siding off the outside and opened up a small whole near the roof of the bump out. Reaching and looking inside, it seems there is no insualation. He said it does not appear to be sheet rocked either from what he can tell. He is not really familiar with these types of fireplaces, but is willing to help me out and pull off the siding and plywood back of the fireplace chase from the outside to add some insulation and whatever else is needed. He thought some "foam insulation board" installed might work better than traditional insulation between the studs to prevent heat loss and air infiltration. He said it doesn't have as high an R value, but it would stop air infiltration better than fiberglass batts. He said air infiltrations seems to be the main issue. Air is entering through the soffit on the roof and just drooping down into the chase. He said he does not see how he could do any sheet rock from the back end on the outside. The only way he could do that is removing the fireplace from the front which would be a bigger deal since it is already tiled/mantled and finished around it on the inside.

What is the best way to proceed with correcting this install from the outside if possible? Any advice from you experts I can give the contractor who is doing me a huge favor here?

[natgastech]

Before you do anything get the manual and review all the "clearances to combustibles" and have your GAS CONTRACTOR do the same. Have them sign a contract that they understand the instructions and they will be liable if a fire were to happen.

[jtp10181]

To do it from the back you take all the siding off on the back wall, then take the plywood off, then take a few studs out. Then you can get in there and insulate and seal off the whole chase. For the back wall you build a standalone wall that will just fit into the opening you already have, pre-drywalled on the inside. You fit that in place and nail it off. Caulk all the edges. Fill the stub bays with insulation and put the plywood back on.

The rigid insulation board might work good also. If you have 2x4 walls in there I would double up 2" board and fill the whole stud cavity. Make sure you caulk around it well, and don't use stuff that melts the foam. I have seen another contractor use the foam, and then cheap construction caulk and it reacted with the foam and melted huge holes in it.


As natgatech said, make sure you maintain the proper clearance to the fireplace and the VENT and it passes through the wall.

[hearthman]

Scott, you need to dig a little deeper. This has been discussed AT LENGTH here at least a dozen times.

Whatever you choose for wall insulation, ensure it is sheathed to stop air movement and cannot fall against the hot fireplace or invade stated clearances to combustibles.

Hearthman

[Scottrichards]

Sorry Hearthman. I know you guys get tired of answering the same questions over and over. I did search through several screens worth of postings. I found lots of posts about what needed to be done, but not and step by step ways on how to do it. When I told the general contractor that it needed to be sealed from air infiltration/insulated/drywall etc so that the fireplace is within the interior envleope of the house as best as possible (using thermoply/tape/vapor barrier, etc. applied from the backside)...he didn't see how that could be done easily. I gave him the info I found off this websitee and later off this tread, and he still does not see how he will have enough room to maneuver to screw in any drywall or plywood inside. He said maybe he could put the plywood and/or sheetrock up by pulling it up against the inside of the studs an holding it up there with some type of caulk/sealant instead of screwing it. He said he needs to make sure of the clearances, and he is not to sure what the options are until he pulls off the back and sees what he has to work withand how much room there is behind the fireplace. He is a real nice guyand just trying to help out. It is a long story but the contractor who I bought my house from screwed up many things with my house and has since went out of business. He hasn't taken the siding or back off yet, maybe there is more room behind there than it looks.

[jtp10181]

Measure the outside dimensions of the chase, I can tell you within a few inches of how much room will be in there. Depth from siding to the corner trim, and width from corner to corner.

Also need to know if the firepolace is flush with the interior wall or sticks out into the room at all. Not talking about any stone or mantle, just the fireplace shell itself.

[Scottrichards]

2' deep x6' wide

[jtp10181]

You should have about 5-7 inches in the back and on the sides 6-8 at the very front but the firebox has a really good taper on it, so to the back of the fireplace you will have around 20" on the sides. This brochure shows the size of the unit shell:

http://www.heatilator.com/downloads/brochures/NOVUS.PDF

[Xavier]

“I have always had a dramatic draft coming out the bottom of the fireplace when not in use. It was too the point I ended up just covering the whole fireplace over from the inside with plastic and not using it. You could see the plastic suck in and out from the draft on really cold and windy days.”

Hi Scott, I have been answering/explaining this for over 30 years now, but unfortunately it is still not understood.

Once you answer the following question you will be able to solve your problem yourself:

Why is the outside air coming in, where is it going and why has it not stopped?

Here is a clue; let’s compare your house to your car’s gas tank. On your car after you drive it for a while you must add gas. There is only one way to add the gas to your car and soon or later the pump stops.

Good Luck
Xavier.

P.S. For a more detailed explanation you can read my web site.

P.S.S. For a final clue read the last line in my closing

[hockey]

I have a basement fireplace... negative draft due to 2nd and 3rd flue... oil furnace and ist flr fireplace cause negative pressure. It pulls the air DOWN the basement chimney. Do you know anyone in Bartlett, NH area who can help with a masonry install of a pellet stove (need to direct vent it).