WeldrDave , What temp would you say is appropriate to run this unit at? I'm used to watching the stove pipe, but since I'm using this double all its a whole different ball game. Burning my "smoke the house out with paint fumes test fire" and boy I'll tell ya what - this unit is going to be a serious heater!!! This double wall is really nice I can just about lay my hand on it where it attaches to the masonry chimney/stainless liner. I have about 8' of pipe before it enters the thimble.