Abstract: A stack exhaust heat recycling system utilizing the heat content of exhaust gases passing through a smoke stack to the ambient atmosphere. The stack includes an inner shell defining a passage to carry the exhaust gases without restrictive draft. Surrounding this shell in any desired configuration is tubing carrying fluids (liquids, gas or oils). Surrounding the tubing is an intermediate shell, insulation and an outer shell. During the passage of the fluid through the tubing, transfer of heat occurs from the gases to the fluid so that its temperature is elevated for use, e.g., as hot water, thus eliminating or supplementing a hot water heater. Other uses requiring elevation of the temperature of water or gas may be similarly utilized.