I have a small Sears wood burner with fire brick lining. It's really not very large, measures about about 3 ft. high, and 20 inches wide, and deep. It have a newer natural gas furnace that is one of those that's supposed to be 99. something % efficient as a back up. Last year I had to use it on those windy -22 degree days to suppliment the wood heater, but this winter I didn't need it yet, nor any previous winter. It's always about 72 to 75 degrees in here when it's burning at full force. I have a bi level, and the upper level is where I live, don't use the lower level much the upper level is 1200 Sq. feet, and the lower level is 1100 Sq. feet. The lower level stays at about 50 degrees. If it get's colder down there I put the furnace fan on to move some heat down there. On days when the sun shines I have to keep the fire very low, or it gets too hot. This house if very well insulated though, I should mention.