How Does a Furnace Work? The Various Components of a Furnace and How They Work

how a furnace works

How Does a Furnace Work? The Various Components of a Furnace and How They Work

(Last Updated On: October 14, 2017)

How Your Furnace Works: Why You Need to Know

While the exact specifics might differ, the basics of how a furnace operates remain the same. The specifics vary depending on the type of heat fuel you use or type of furnace, but understanding your furnace helps troubleshoot issues. Additionally, understanding your furnace makes you a savvy homeowner and helps identify solutions to any problems. For our discussion below, we are using the example of a gas-powered forced air heating, ventilation, air conditioning (HVAC) system. Without further ado, here’s everything you need to know about how a furnace works.

Furnace Components and How They Work

To first understand how a furnace works, it helps to know a little bit about the furnace components. All furnaces contain a heat exchanger, burner, ductwork, plenum, blower, and flue or vent pipe. Additionally, some furnaces include an air conditioning unit responsible for cooling during summer months.

The heating process begins with the burner. Once the temperature drops low enough to trigger the furnace to run, the burner engages. This drives the gas to the heat exchanger. For reference, your thermostat controls the burner. Depending on the size of your home, your furnace contains either a single burner or dual burners (which heat larger volumes of air).

Next, the heat exchanger intakes air and turns the gas and air into heat, which ultimately moves through your home’s ductwork. Then, combustion occurs. Combustion occurs when fuel combines with air and ignites, which creates heat. Finally, the heat air transfers into the air distribution system, which includes the blower.

How the Furnace Heats Your Home

As the combustion process happens, outside air enter the system through a separate vent. The outside air mixes with heat. Next, the air warms to the correct temperature and distributes throughout the house through the ductwork. However, this new and fresh outdoor air requires filtration. As a result, the filtration process removes dust and debris before it is stored in an enclosed space known as the plenum of the furnace.

Next, the he blower in your furnace engages and blows heated air through your ventilation system or ductwork. Ensuring a clean blower that is in good working condition helps the furnace blow hot air when you need it. Additionally, the air distribution system maintains responsibility for adjusting the temperature of the air to what is set on the thermostat.

The flue and vent pipe of your furnace is responsible for keeping the air in your home safe to breathe. It does this by exhausting harmful byproducts from the combustion process, such as carbon monoxide and other noxious fumes, outside your home. The flue opens and closes accordingly to ensure that there is no backup of this potentially dangerous exhaust into your home.

Finally, the ductwork of your HVAC system allows heated air to be distributed throughout your home. Therefore, ensure ducts remain clean and free of blockages or debris for optimal air circulation. Additionally, air circulates through the furnace air filter, which helps clean and purify the air. This is important for maintaining your HVAC system and helps cut down on allergens and odors in the air. Plus, this helps cut down on the amount of dusting and vacuuming required in your home.

Once the temperature in your home reaches its set level, this process stops until the next time heat is required.

Some furnaces include an attached humidifier, which adds moisture back into the heated air before sending it through the ductwork. This helps create a more comfortable environment.

Heating and Air Conditioning

For furnaces equipped with an air conditioning unit, the AC unit engages and the cooling process begins. It first activates the AC evaporator coil, which removes heat and humidity from the air. Then, the condensate line moves excess moisture to a floor drain in your home. Next, the compressor expels heat outdoors by circulating a refrigerant through the evaporator coil. This cooled air then makes its way back to your furnace unit for conditioning and the addition of humidity. Finally, the cooled air passes through the air filter and through the ducts into the various rooms of your home.

Finding the properly sized furnace helps homeowners avoid a common issue. A furnace that is too large for a space will short-cycle, causing increased wear and tear on the unit and spikes in electricity. A furnace that is too small for a space will run continually during cold weather, resulting in higher energy consumption and ultimately increased costs.

A qualified HVAC professional helps you determine the best furnace for your needs and keep it running in peak condition.

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