The photo below shows the furnace vents going through the rim joist ... usually right next to the furnace. This is the combustion air duct I showed at the beginning of this post.

It is just as important for a furnace to get the correct air supply to support combustion as it is to vent it correctly. A furnace must be supplied a specific amount of fresh air per cubic foot of gas ...

Most sealed combustion units (combustion air for the furnace is drawn from outdoors, the firebox in the furnace is sealed, and the exhaust gasses vent outside through a PVC pipe) draw combustion ...

it helps illustrate why modern sealed combustion “direct vent” appliances that take all of their combustion air from outdoors make so much sense. Not only are direct vent appliances more efficient on ...