Does anyone have one of these? Do you use it as your primary heat source? Have you ever had a problem with oxygen depletion? I ask because the guy setting my propane tank said my heater isn't safe as a primary heat source, and right now my wood furnace is FUBAR (cracked heat exchanger, among other things) and I'm not sure it can be fixed (got a guy coming out next weekend to take a shot at it). I was hoping to be able to use the wall unit if the woodstove's shot. Now, I don't know WHAT to do!