Last night the door flapper on my 1970's vintage Olson wood furnace came off due to a broken hinge. I am hoping that I can get the neighbor with his welder to weld it together in a couple of days. What I am asking; Is it safe to run a wood furnace without the door flapper? I noticed that the smoke backs out through the door when I stoke it. If I open the door slowly I can avoid getting the smoke. Its a cold climate here in Northwestern Ontario and temperatures are going back down in the -30s Celsius at night again for the next few days. I don't want to run the oil furnace at these temps, as it cannot provide the comfort level the wood can.