Providing Enough Combustion Air
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If you are remodeling and tightening a garage or basement that contains a fossil-fueled heater, water heater, or clothes dryer, you need to be aware of its need for combustion air. As you change the way that air flows through the space, you want to make sure that you don't make it more difficult for the equipment to exhaust gases to outside.
When you tighten the space by air sealing, you may be decreasing the amount of air that is readily available to the equipment. This can cause the equipment to backdraft, which means the burner sucks exhaust air back down the flue into the house. At a minimum, you should have a service person check the equipment's operation in the remodeled space after you have finished all the work there. They should check for depressurization in the space under worst-case conditions.
If you have a forced air system (that is, one that uses ducts to transport heated or cooled air around the house), you may be able to make the system safer by sealing leaks in any return ducts located in the remodeled space. Other ways to make sure the equipment operates safely are to install a powered exhaust system to force combustion gases up the flue, or to upgrade to high efficiency sealed combustion equipment if you are considering replacing your furnace, boiler, or water heater anyway.
In warm climates, you may want to isolate the equipment room from the living space and install vents in the wall to provide air to the equipment. Don't do this in a cold climate—it can create hazardous conditions.
Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)