I'm in a 1800 sq ft ranch with a 3/4 basement. I have an old wood furnace in the basement as well as a NG furnace (centeral air) that sets next to it. I ran a 10" line from the top plenum on the wood furnace and connected it just above the air filter on the NG furnace. I run the blower on my NG furnace/centeral air unit almost all year long 24/7. My wood furnace has a forced air draft that's controlled by it's own thermostat that I have mounted in the living room. The centeral air unit is constantly pulling some heat off the furnace and pushing it into the bedrooms and throughout the house. When the temps get low enough to kick on the draft blower, the WB Furnace starts getting hot until the WB thermostat trips turning on the blower on the WB Furnace which then starts pumping the heat off the WB furnace into the ductwork. I typically have the draft thermostat in the living room set about around 74 degrees. The centeral air thermostat is normally set somewhere between 69 and 71 degrees depending on how cold it is outside, and what the wife want's the house to be like. The NG furnace rarely kicks on during the day. I think on a normal day with lows in the lower 20s, it will kick on a couple of times just before I wake up in the morning. Just enough to keep the dust burned off. NG bill runs around $35 in the summer, and between $45 and $75 in the winter. Ironically, its the warmer months that cost me more because its too warm out to run the wood burner.
Works well for me...