Whoever installed the gas furnace in my little house ran the vent pipe up into the attic, then over to and out the south wall of the attic rather than up through the roof. They just hacked a hole through the cement fiber board siding, stuck the pipe out, glued on a grill cap, and were done. The home inspector didn't notice this. I did after I moved in. I squirted some foam insulation around the pipe, stopping up the gap, cleared out the wood wasps (catch and release). But I need to fix this properly and I don't know how. Would some kind and knowledgeable soul please give me a step by step? Thank you very much. M.