Last year I had a new furnace installed. It is in the crawlspace of my house, on its side--as was the previous furnace. The top side of the furnace (near the end that would be the bottom if it were standing upright) has two holes with black plastic boots, one of which has a pipe (exhaust?) fitted into it. Today I realized that the other hole has no cover--you don't notice it if you're looking straight at it, but if you are leaning over it (between the floorboards and the unit) and looking down, it's an empty hole. You can see the wiring at the base of the unit down inside. Should that be left open like that? I called the installer and he can't really remember the install job but says it passed their inspection so it must be okay. I'm thinking that if the furnace lasts 15 or more years that's a lot of dust landing down around those wires and I'm wondering if some kind of cover plate should have been put on the unused hole. Any advice?