Three years ago, I purchased and installed a Keystoker A-80 warm air furnace, and from the start was completely satisfied with it. The only difference between the A-80 and A-150 is size, and even though I intially considered the 150, I just didn't need the additional heat it would deliver and opted for the slightly smaller A-80 in the name of efficiency. My house is about 2,500 square feet and is pretty well insulated, however the living room is in the old part of the house and the walls are not insulated very well, and the windows are old and not at all energy efficient, and as a result, it's the coldest room in the house, and where the thermostat is located. In spite of this, no matter the temperature (lowest so far has been -29) my house has been nothing but warm and cozy all winter long. I run my furnace based on the outside temperature. Once the daytime temps don't get out of the 40s, I'll start the fire. Last year, early to mid-November to mid-May, I burned coal. Expecting a cold winter last year, I had a total of five 2,400 lb. skids of Blaschak rice coal on hand, and burned almost four of them. Consumption for November-December was one skid; January and February, one skid each, and April-May, not quite one skid. My oil usage last year was about 150 gallons. So far this year, since shutting down the coal furnace it's been about 40 gallons. I can also tell you that my basement (block walls and cement floor in the newer part/dirt floor and cobblestone/uninsulated wood walls in the old part) stays comfortable enough that I can work down there without even a sweater in the coldest part of the winter. Would I do it over again? Absolutely. The Keystoker warm air furnace is everything the manufacturer claims, and then some!