Sorry, let me clarify. When you enter the garage, in the corner there is a closet. There are two steel doors that lead into this closet from the garage with no access through the house to the closet. The doors appeared to be weatherstipped and sealed up pretty tight. There is a wood platform that elevates the water heater and furnace off the ground to meet the 18" requirement. There is a metal louvered grill in the top of the platform (where the units are sitting) that leads into the hallway of the house. There is also a 4" diameter metal pipe coming down from the attic space and terminates at the base of the water heater. Could this be correct? Any ballpark guesses?