Industry- wide, it's as follows: 80% heat exchanger 8% Propane 6% Kerosene / Oil (The remainder is split between "no heat source" and electric.)
We use two heat sources for our Heat Exchanger: 1. Engine Exhaust -Stainless tubing insulated with hi-temp fiberglass tubing 2. Blower exhaust to limit heat rise @ 230°. Larry
Powerclean Freedom XT uses an engine coolant hx, exhaust hx, blower exhaust hx, backed by a little giant 3HT high PSI. When cleaning tile @ 1200psi the exchangers have a hard time keeping the heat. When I get into a bad resi or the greasy restaurant, I fire up the Little Giant and can keep 250*+ all day long.
I think heat exchangers are one of the best thing that has happened to the industry. They avoid the cost and inconvenience of propane.
We make all three now: Propane, Oil-Fired and Heat Exchange To my knowledge, we're the only manufacturer who does. Each has a strength and a weakness.