Anyone ever watch "Homestead Rescue". The head guy had pics on his home where he made a square arrangement of his flue pipes. Off the stove he teed, one went left, another tee went right, a short straight that joined both side with tees back together. All this to collect heat off the pipes.
Then an episode came along where his house burned down! Nothing ever said what caused it, but I have my idea!
A flue pipe running cold will collect creosote fast.
