How Furnaces Work

You know that your furnace makes your home warm and toasty in the winter. But what exactly happens in your heating system to make sure that the temperature of your property is comfortable no matter what is happening outside?

All modern furnaces use a thermostat that allows you to set your desired temperature. When the temperature in the room goes below this set point, the heating cycle begins.

The cycle begins with the inducer fan. The purpose of this fan is to make sure there is adequate airflow throughout the furnace. The fan pulls air from the inside of the house through an air exchange vent or from an exterior air conditioning unit or other outside vent. It pulls this air through a filter and into the furnace.

In a gas furnace, the next step is the opening of the gas valve, which allows the gas to flow through the burners to the igniter (or, in older models, the standing pilot). The igniter lights the gas through heat or a spark. Once the gas is lit, the igniter is disengaged. The furnace burns the original gas for around two minutes, ensuring that it reaches a warm temperature.

In an electric furnace, the electric heating coils are activated once there is proper airflow from the inducer. These coils convert electrical resistance into heat energy.

Once the air in the furnace has been sufficiently warmed by the gas flame or electric heating coils, the blower forces the warm air from the furnace through the heat exchanger. The heat exchanger warms the air to the established temperatures and then sends it to the duct system. The air moves through the duct system and out through the vents of your homes.

The furnace continues to heat and blow air until the thermostat registers that the correct temperature has been reached. At this point the gas supply or heating coils are turned off. The blower will continue to run for a few minutes to cool off the heat exchangers, preparing your furnace for the next time the cycle will be needed.

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