The EZBoiler outdoor furnace is a natural draft system. It burns organic fuel and heats the water that is in the water jacket. The furnace water jacket completely surrounds the firebox. Water is pumped through an insulated line that is buried in the ground and attaches to a indoor furnace coil that is mounted in the duct work of your home. When your home calls for heat, only the furnace blower turns on, blowing air through the furnace coil and heating your house with the heat created in your outdoor wood stove.