Drafty Combustion Air Duct at the Furnace

December 3, 2002

Question from Steve in Calgary, Alberta -----

Hi Shell,

First, what’s the vent called which is attached to the side of our furnace and brings cold air in from the outdoors? My guess is that its purpose is to balance the air pressure inside our house with the outside air pressure. Second, we get a lot of cold air from this vent in the wintertime. (not a draft but definitely cold air). Is there anything we can do to insulate the end of the vent without affecting its purpose?

Much Appreciated.

Steve

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Dear Steve:

The “combustion air” duct you are speaking of is very important and it’s there to provide adequate combustion air for your furnace. Most folks don’t realize that to support proper combustion, it takes 10 cubic feet of air for every cubic foot of natural gas burned.

Some people who don’t know any better will stuff a rag in this duct in the winter because they think it’s letting in too much cold air and don’t realize the furnace needs that air to support combustion. Blocking off this duct could cause your furnace to starve for air and could even create a potentially dangerous down-drafting (negative pressure) situation.

The answer, especially in colder climates, is to install a Hoyme Damper (motorized damper) to stop the inflow of cold air when your furnace burner is off. Contact Hoyme Manufacturing in Camrose, Alberta at 1-800-661-7382.

Make sure you have the Hoyme damper installed by a licenced gas fitter because he will be installing a relay that opens and closes the damper in concert with the gas valve. It is important for safety reasons that this is done properly.

“Its Just That Easy”

Shell