Fresh Air Inlet for Kuuma Vapor-Fire Furnaces

If you have a very tightly sealed home or experience smoke getting into your home, you likely need to add a fresh air inlet into your furnace room.  It’s common that when running the laundry dryer, range hood, or bathroom exhaust fans in a very tight home, you can actually reverse the draft in your chimney.  The solution to this is adding a fresh air inlet.  When done correctly, this will allow adequate combustion air for your wood-burning appliance without flooding your furnace room full of cold air.  As you see in the diagram, we suggest putting a vent through the sill plate of your home and using a dryer vent cap on the outside; inside the furnace room, run a simple 4″ flexible duct from this dryer vent cap down to about 6″ above the floor.  Place a Sonotube (often used for concrete deck piers) around the duct tube.  Cold air does not like to rise, and the Sonotube will prevent the cold air from flooding the furnace room.  The furnace will draw only as much air as it needs to burn effectively.  In many states, a fresh air inlet is code for new homes.  It costs about $20 to make one of these.

Fresh Air Inlet (PDF)