Yep, is loaded question! Depends I would say on what your home is like to heat, if big old farm house on top of hill and drafty, 80lb. a day is probably not bad. In my case we have a Hitzer 354, burning 30-40lb. a day, but fairly new house, and tight. But I would bet your coal usage cost is still about a third of whatever you were heating with befor, unless it was wood. Expect others will jump in here soon.