No problems here at all. I've been keeping a meticulous count of what has been going into my wood boiler, for conversation's sake. I put 16 pieces of mixed hardwood and pine in this morning, on a good coal bed. 16 pieces average 5-6" diameter and 20" long. I will add another 4-6 pieces tonight just after dark. That will keep me going, in sub-zero temperatures, for 24 hours. I heat 4300 square feet of living space plus enough hot water for a family of 7. This morning I could have shoveled 40-50 lb of good charcoal out of there (and might do so for future use). It's awesome to see a bed of coals a foot thick, 3 ft square, glowing orange and a mass of small blue flames everywhere. House stays pretty much at 65 degrees, boiler set point is at 180 high, 170 low.