Created Friday 30 December 2022
A modern furnace may need power for a number of reasons.
First, the control system is electrical. When the thermostat calls for heat, it does so by closing an electrical circuit, starting the furnace.
A modern high-efficiency furnace, regardless of fuel, may have a draft inducer. If it vents out of the side of the house, this is a certainty, but furnaces that vent through the roof may have one, also.
If your furnace uses a spark or glowbar igniter, that needs power. Furnaces with a standing pilot don't need power for this stage.
If your furnace is oil-fired, you will need power to turn the fuel pump.
You will need power to open the fuel valve.
If your furnace uses a "gun" type burner, you will need to power the blower that pushes air into the combustion chamber.
Finally, you will need power to turn either a blower (forced air) or a circulator pump (hydronic). Steam boilers, however, do not need this.