The Dual Fuel System was designed to work with a new or existing furnace system.  Natural gas or propane is used to fuel this system. During the cooler season the dual fuel system brings heat indoors from the outside air. A forced air furnace will provide heat support also during these colder months. In warmer weather it brings the heat from inside your home to the outside.  The forced air furnace and dual fuel system work together to keep a moderate temperature inside your home. When the temperature is too low outside to bring heat in, the forced air furnace automatically kicks on to provide your space with the heat you need in the most efficient way possible.