:confused: I have a 2 family that has 2 furnaces and a water heater w/ a total of 230000 BTU the mech room it is in is 1229.2 cubic ft the whole basement (finished) is 5562.2 cubic ft I installed four 16''vents one 12'' one 8'' and put a 24''x30'' vent on the door.The 16'' vents I put 2 up high & 2 down low. Do I have enough makeup air or do I have to bring in outside air. The house is 108 years old granite foundation not exactly air tight..

The big question is are the furnaces high efficiency? Do they use plastic pipe to vent? If so are there two plastic pipes attached to each furnace?

Code stipulates the amount of combustion air but with the right kind of furnace the install instructions will allow a great reduction or eliminate the requirement all together.

The manufactures instructions always over ride the code and that exception is listed in the code book or AGA.