Currently, 12 hours is the limit. It's 7.1 and dropping, and inside it's 68.6 and slooowly climbing. T-stat is at 2.5 or else I'll max the cat, it's @ 1650 and stable with an hour and a half fresh load burning right now. if it was blowing, forget it, I went through that a few days ago. I'm sure my isulation issues, and air infiltration a major factors. The old stove was good for 8-10 hours in nasty weather, up to 12 when it didn't get below 20 at night. The old stove, if I really needed the heat, would perform. The BKK seems like it has a heat "govenor" on it- not enough of "this"and this suffers, too much of "that" and that suffers. You should get a flue probe, just to see what is actually going up the stack.