Well, Finally I purchased the 1950 Epa wood furnace. Very well built unit built by SBI, marketed by US Stove. The furnace is set up just like a furnace. Runs off a thermostat with natural draft, no forced draft. 71.4% efficiency rating by the testers. What I am trying to figure out is the caddy add-ons are made to use the current central furnaces blower. This one is setup with the blower in the back on the bottom then pushes air around the firebox through the heat exchanger and out to the ductwork. So this units got a 4 speed 1300 cfm blower with 2 furnace filters. I was thinking about putting a damper in each plenum of the central furnace and the wood furnace. This way when one or the other runs, they can't backfeed into eachother. But the issue I am seeing is tying both the returns together to share the main return. The woodfurnace will be set 4 or 5 degrees higher than the propane furnace. I'm afraid of heat from one or another feeding into the returns of either and causing problems. This will only happen if both decide to run at the same time. I'll make dampers for the plenums, but like said undecided about the return air. I've heard nothing but good about these furnaces, and got a good deal on this one. I was told that after 25 minutes they produced no smoke! I bought this as a step for the future, the environment, and less wood.