The GF heaters function on the principle of indirect fired oil heating. Hereby a powerful fan is used to force air through a heat exchanger. The burner is situated inside the heat exchanger and heats the inside surface of the heat exchanger. As the air passes over the outside surface of the heat exchanger, the heat is transferred to the air.

The heat exchanger is fitted with a chimney that allows the combustion gasses to be vented through the chimney to the outside. Hereby none of the noxious combustion gasses released by the combustion process are released into the air stream exiting the heater. The combustion chamber is designed to be very efficient and up to 88.5% of the heat released by the combustion process is transferred to the air stream. The GF heaters operate on oil, kerosene or paraffin.