I've been hunting for a while for a decent wood stove. I may have found one, but I'm not sure. It's a wood/coal furnace, sold by Northern Tool & Equip. Decrption says it can hold up to 9 hours of heating per load, has 2 raised 8" outlets for duct connection, and safety tested to UL391. What does the safety testing numbers mean? Do I "have" to hook up ductwork? Optional stuff is a draft kit with thermostat, and cold air return. Do I need those things?