Lighting the Torch
Gas is the fuel that fires the flame that heats the air that warms your home, but electricity is the spark that lights the gas. The flame is not roaring all the time or just ignites spontaneously. Think of the athlete igniting the Olympic torch.
A low voltage electric signal from the thermostat opens the valve that controls the amount of gas flow and therefore the flame. A solenoid coil in the valve senses gas and ensures flame to prevent an explosion or leakage, then opens wide to let the heating begin and shuts down when the desired temperature is reached.
All that heated air must be moved through the ductwork and distributed room to room to create the comfort and this is done by a motor-driven fan which is the largest use of electricity in a gas furnace. The motor turns on and shuts down according to the relationships between flame, heated air and the thermostat setting.
Known as a draft inducer, a second fan is employed to remove the toxic fumes that are the residue of the burned gas. These fumes which can be deadly are usually pushed through a PVC pipe to the exterior and released safely into the atmosphere.
The amount of electricity used to ignite the flame is very small, phased through a low-voltage impulse wire, nearly too small to even show on your meter. Most of the electrical energy contributing the critical role of powering the two fans in gas furnaces adds up typically to less than 600 watts at any given time or about the same as a few light bulbs.
While gas furnaces are much more efficient and less costly than any kind of electric heat, they are useless (and even dangerous) without that little bit of electrical help.