We have one where propane is used to heat a glycol solution in a tube and you put the PVC into the tube. It is a bit messy, but very fast once you have the glycol up to heat. I think that it is a Greelee product. Don
The exhaust pipe trick only works on the ends of the pipe and tends to collapse the pipe (gets to hot in one spot)and the ends have to be cut off because couplings and connectors wont go on.Just creating more work for yourself....look at the web site pvcbender.com it works great.