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dmcmillen 06-27-2009 08:38 PM

Gas furnace in SPF sealed attic
I have a gas furnace in an attic that I am getting ready to insulate with spray foam on the roof deck. This will seal the attic area in except for any infiltration from the living area below. I don't think there will be enough oxygen to fuel the furnace and I don't want to open to the outside to ventilate the attic which would defeat the purpose of sealing with the foam, because instead of the attic space being 5-10 degrees difference from the living space, it would then be the outside ambient temperature.

Does anyone know how to solve this problem? Is there some type of air exchanger that would feed the furnace???

I would appreciate some help here.

Thanks, David

Plumber101 06-27-2009 08:51 PM


Are you trying to seal off all ventalation to the attic?

What do you live? State?

dmcmillen 06-27-2009 09:21 PM

The purpose of applying spf (spray polyurethane foam) to the roof deck is to seal the attic area in. It is sprayed on the roof deck and down over the soffit area to effectively seal in the attic. The temperature in the attic is then only 5 - 10 degrees differential from the living area below. The advantage of the foam over traditional insulation like fiberglass or cellulose is that it insulates and seals out all infiltrating air. It is usually not completely sealed because there is still air infiltration from the living area below. The result is less wear and tear on the hvac equipment, less loss/gain in ducting, and so on. In some new construction where the walls, floors and attic are sealed, an erv or hrv vent system is required. To spray foam the attic deck is a common practice.

My question of course is whether there is enough oxygen to fuel the furnace. If not, is there some type of air exchange system that can be installed that will feed the furnace but not compromise the seal.

Plumber101 06-27-2009 09:26 PM

Roof vents, gable vents or cross ventalation

kenmac 06-27-2009 09:39 PM

#1 I wouldn't seal all outside air from comming into my attic... It's your house so, it's your call. If your furnace is so equipped you can add a pipe for combustion only to the furnace... If it's an 80% furnace you probably won't have that option

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