This is the completed (as far as I plan on completing it) propane forced air heater. The fan is from a kitchen exhaust vent hood. The rest is just various pieces of 6" and 8" ductwork and 1/4 galvanized piping. The final piece to get the flame right was the polyurethane can in the back-center of the inner tube. In this run I estimate it to be putting out around 100000 BTU, but by reducing the amount of air bypass I can get it up to at least 200000 BTU, limited only by how much gas the 20 lb. cylinder will put out. For those interested I made a forum thread covering the process. backyardmetalcasting.com