DaveHo; Yes an NG/Propane furnace, especially one in a confined area, needs combustion air. But the amount is based on the amount of BTU's the furnace burner gives out
.Example; For a home of 1500 sq ft the size of the combustion air, for say an 100,000 btu burner, would only need approx 28" of air (6" diam pipe) at the most, not 400 inches !!!!
Last edited by Hube; 09-16-2010 at 08:51 AM.