Installing a new owb and cant figure out the best place to put my exchanger. I have a 80,000 BTU 80% downdraft propane furnace with the A/C coil below it before it runs through the floor into the ductwork. 12x20 outlet. cold air return overhead will hold 20x20. I have read that installing the heat exchanger below the furnace could heat up the electronics, also read that putting it above the blower would heat up the blower. Whats best.I can install it under the AC coil which would put it about 16 inches below the furnace.