Thread: Sealing the furnace door

In a interior closet mounted combination gas furnace and AC unit, waht is the tradeoff versus fresh air for the gas flame, versus sealing the door to prevent carbon monoxide from entering the home ?

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I guess it depends upon a couple of things Gene. First of all, what type of furnace are we talking about? Is it a 90+ efficiency furnace with a combustion air intake pipe routed to the exterior? Or is it an 80% efficiency furnace that draws combustion air from the square footage of the space around it?

If it is an 80% furnace and the closet housing the furnace is sealed with no provision to allow combustion make-up air into the closet, then you will most likely have a CO issue because it will not be able to properly combust all the gases due to lack of make-up air. Sealing the closet will create the very type of CO issue you are trying to avoid in the first place.

The bottom line is all gas-fired furnaces need a combustion air source. It's just a matter of where it comes from.

Nick, it is an 80%. Thanks for the feedback.

Gene

A vent pipe coming down from the attic for combustion air and a screened vent in the ceiling for any gas/co. Seal the closet off from the home altogether. There is no home I have been in with the very minor exception of a few that are not vented like this. You are not robbing the home of air and you are not chancing venting any unwanteds into the home.

Problem with a screened duct is that is eventually blocks up. Not allowed in our area.

That's because half of them are not boxed up above the insulation. They just push the insulation out of the way. I guess there is a right way and a wrong way for everything. I guess in a perfect world folks would have their HVAC system serviced on occasion.

If you're going to recommend sealing up the closet recommend fan powered combustion air also.
It is the only one that will work reliably under all conditions.

Most high/low passive combustion air ducts only exhaust air out of a room not supply it.