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: June 29, 2017)

As long as your home is a comfortable temperature, you might not give much thought as to how your furnace works. But as soon as this vital component of your home stops working, it can be rather difficult to ignore.

How Your Furnace Works: Why You Need to Know

While the exact specifics might differ depending on the type of heat fuel you use, or the specific type of furnace you have, the gist of how a furnace operates remains the same. Understanding how a furnace works cannot only help you to troubleshoot issues and solutions when you have a problem, but will also make you a more savvy homeowner. 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 components a furnace consists of. All furnaces have a heat exchanger, burner, ductwork, plenum, blower, and flue or vent pipe. Some furnaces also have an air conditioning unit responsible for cooling during summer months.

The burner in your furnace is where the heating process begins. Once the temperature drops low enough to trigger the furnace to run, the burner engages to deliver gas to the heat exchanger. The burner in your furnace is what is controlled by the thermostat. Depending on the size of your home, your furnace may have a single burner, or dual burners in order to heat larger volumes of air.

The heat exchanger in your furnace then intakes air and turns the gas and air into heat that will ultimately be sent through your home’s ductwork. This process of fuel combining with air and being ignited to create heat is known as combustion. Once the air has been heated, it is transferred to the air distribution system, which includes the blower.

While this combustion is happening, outside air is being brought in through a separate vent, in order to be mixed with the heat to the correct temperature, before being sent through the ductwork. This fresh, outdoor air must first be filtered from dust and debris before it is stored in the an enclosed space known as the plenum of the furnace.

The blower in your furnace will then engage in order to blow the heated air through your ventilation system, or ductwork. Ensuring that the blower is clean and in good working condition will help ensure your furnace blows hot air when you need it. The air distribution system is also responsible 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 is what allows the heated air to be distributed throughout your home. It is essential that ducts remain clean and free of blockages or debris in order to allow for optimal air circulation. While circulating throughout the system, your home’s air will go through the furnace’s air filter, which helps to clean and purify the air. This is important for maintaining your HVAC system and helps to cut down on allergens and odors in the air. It can also help to 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 to create a more comfortable environment.

Heating and Air Conditioning

If your furnace is equipped with an air conditioning unit, the AC unit will engage in order to cool the air during summer months. It first activates the AC evaporator coil, which removes heat and humidity from the air. Then, excess moisture is carried by the condensate line 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, before finally passing through the air filter and through the ducts to the various rooms of your home.

It is important to ensure that your furnace is properly sized for your home. 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 can help you to determine the best furnace for your needs and keep it running in peak condition.

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