We have a yukon eagle wood/coal/oil combo furnace installed 9 yrs ago and have always had trouble with efficiency. We use around 20 cord of wood a season or 275 gallons of fuel oil a month (late October to early April). The thermostat is set around 65-70. The installer used flex duct instead of tin and 3 cold air returns all on the ground floor. There is between 1 and 3 in each of the upstairs bedrooms, the living room has 4 heat ducts and a cold air return, the dining room has two heat ducts and a cold air return, the kitchen has 2 heat ducts and a cold air return, the entry has one heat duct, and the laundry room has one heat duct. The house is almost 3000 sq ft. Please let us know if there is any way to make the furnace more efficient or how we could burn coal in the furnace.