Take a look at the Hitzer installation manual:http://www.hitzer.com/documents/product ... 0Final.doc
Here's what Hitzer says NOT to do:
Do not have supply hot air flow downward as this will not allow the Hitzer Furnace to operate properly without electricity
Do not have the supply air flow back into the blower of existing oil or gas furnace. This will damage the existing furnace controls and/or void any warranty.
Do not have hot air from gas or oil furnace flow downward into the Hitzer Furnace and flow out the Hitzer Furnace to existing duct work.
I had my Koker installed by the dealer. Big mistake. He connected the hot air output into the cold air duct on my propane furnace. When the furnace blower wasn't on, all my heat drifted into the cold air duct. My "heat" ducts were cold when the blower came on, blowing cold air until they warmed up again. I reinstalled the Koker, running the heat duct into the top of the furnace plenum and installed baffles to close off the propane furnace from the Koker. MUCH better installation. Now all my idle heat drifts up the heat vents as it should.
You're asking good questions. You'll do a good installation I'm sure.