I can't get much heat from this unit. My old furnace had no problem heating the house but we are constantly feeding this guy. It burns clean but I don't know where the heat is going. I've been doing some research and noticed on a diagram that the small square holes on both sides of the ash box are air inlet holes. There is always a soft flow of air coming out of mine. I assume it should be sucking air in. Anybody know if this is normal?