Multi-Fuel Furnaces
Furnaces designed to burn more than one fuel are called multi-fuel furnaces or combination furnaces. These furnaces are designed to burn oil or gas in one combustion chamber, wood or coal in the other, and automatically switch between the fuels when the situation warrants (Figures 13-16 and 13-17).
The solid-fuel combustion chamber of these furnaces burns either coal or wood and does so much more efficiently than standard coal or wood stoves. The other chamber uses an oil burner, gas burner, or electric resistance heater to generate heat in the same manner as in a single-fuel furnace. Either combustion chamber is capable of heating an entire house.
The operation of the furnace shown in Figure 13-16 is controlled by a Honeywell two-stage thermostat. The thermostat is equipped with indicator lights to indicate which fuel is being burned.
Wood or coal can be used as the primary fuel with oil, gas, or electricity as the automatic backup; or oil, gas, or electricity can be used as the primary fuel with wood or coal serving as the backup.
