We had about 6 feet of single wall pipe running from our wood stove to our double wall stove pipe chimney that runs through the upstairs. The single wall pipe worked well and radiated a lot of heat back into the room. Well when the owner of the company whom installed the pipe came out he realized we were 2 inches short of the 18 inch clearance for the single wall pipe. The only place clearance was an issue was the first foot up near the ceiling because of a bump-out ceiling molding. Anywho, instead of just running the 2-wall pipe that has a 6 inch clearance (think it is a single wall with a heat shield, not sure technical name for it) only down a foot from the ceiling where the clearance was an issue then continuing the rest of the way with single wall, they ended up running the 2-wall pipe ALL THE WAY down to the wood stove. Now I am finding the wood stove doesn't put off nearly as much heat as it used to with the single wall stove pipe. Will a 2-wall pipe really have that much of a difference when it comes to radiating heat that I would notice it when heating our downstairs. It used to get up to 78 degrees down here within an hour, now it seems to be struggling to even maintain 72 degrees after hours of burning and re-loading with wood. any input would be very appreciated.