After using an inefficient box type wood stove, for many years and burning about 2.5 cords of wood per winter, I bought an efficient Country Comfort fireplace insert. It was great. it has a catalytic combustor , and can burn dry wood like a gasification stove. All combustor stoves regardless of fuel, need air, and if that air comes from the house, cold air has to come in to replace it or the house would drop pressure and starve the fire of combustion air. When building the chimney, I put PVC ducts in the stonework so the air could be brought in from outside. What a difference that can make. The colder it is outside, the colder the replacement air will be, and if it has to pass through the house to get to the stove, you will have a drafty house.