I am installing this fireplace. We are building in Vermont, and can anticipate very cold weather. My thought was to duct the combustion air from the basement and the positive pressure air from the outside. It appears that the positive pressure air duct can be bi-passed manually?? Should I also bring combustion air from the outside if feasible? Can the large potential delta T's cause any burning difficulties? I need to go about 10' to get outdoors, so one 6" pipe is OK, but snaking both through the joists is a bit trickier! I am not using quadrafires air cooled chimney if that affects anything.