How Does A Furnace Work?

How Does A Furnace Work

Anthony Barnes

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Have you ever wondered how a furnace works? If you haven’t, then you should know that furnaces are used to heat homes and businesses. They also provide hot water and air conditioning.

What Is A Furnace?

Furnaces are machines that burn fuel to produce heat. The combustion process creates heat energy that is transferred through the ductwork into rooms or buildings, heating your home.

A furnace uses either natural gas or propane to create heat. These fuels are burned in a burner at high temperatures.

This causes the gasses to expand and turn into steam. The steam is then circulated throughout the home or building.

A furnace can be electric-powered or fueled by natural gas or propane. Electric-powered furnaces use an electric motor to circulate the heated air around the house.

As the name suggests, gas-fueled furnaces use a gas valve to control the flow of gas.

The temperature of the air inside a room will rise when it passes over the heating elements. The amount of time required for this to happen depends on the size and type of furnace. 

Some models have thermostats that allow homeowners to adjust the temperature of their homes, and these can be great for saving energy when required, while still keeping you comfortable in your home.

Parts of A Gas Furnace

In order to have a better understanding of how a gas furnace works, it can be useful to have an overview of the parts that help it to operate. The main elements of a typical gas furnace are:

  • Burner

This part of a gas furnace is responsible for producing hot air. It consists of two burners (one at each end) and a blower fan.

  • Blower Fan

This is the part of a gas furnace (see also ‘Furnace Pressure Switch Stuck Up? Common Causes And Troubleshooting‘)  that circulates the heated air throughout the entire house.

  • Air Filter

This filter removes dirt and dust particles from the air.

  • Heat Exchanger

This is the part that transfers heat from the burner into the air. 

  • Thermostat

This controls the temperature inside the house.

This valve prevents the flow of gas if the pressure becomes too high.

  • Pilot Light

This light helps to start the pilot flame.

  • Vent Pipe

This pipe allows the combustion gasses to escape outside.

  • Supply Line

This is a line that connects the furnace to the main supply line.

  • Main Supply Line

This is a large pipeline that carries the gas from the source to the furnace.

  • Regulator

This regulates the flow of gas to the furnace.

This tank stores excess gas during periods of low demand.

  • Control Panel

This panel contains all the necessary information about the furnace.

  • Condensate Drain

This drain collects any water vapor that condenses on the evaporator coil.

  • Evaporator Coil

This is the part that absorbs the heat from the furnace.

  • Exhaust Stack

This pipe discharges the exhaust fumes out of the building.

  • Return Air Ducts

These ducts carry warm air back to the furnace.

  • Remote Start Switch

This switch turns the furnace on automatically when the thermostat calls for heat.

  • Thermostat

This device senses the room temperature and then adjusts the heating accordingly.

  • Wiring Harness

This is used to connect the wires to the control board.

Types Of Furnaces

The most common types of furnaces include:

  • Forced-air systems: These systems force warm air from outside the house into the interior.
  • Radiant floor systems: These systems use radiant heaters to transfer heat directly to the floor.
  • Steam systems: These systems use steam to heat the air instead of burning gas
  • Heat pumps: These systems use electricity to move heat between two different places.
  • Hydronic systems: These systems use water as the medium to transport heat.
  • Boilers: These systems use water to generate steam.
  • Stoves: These systems use fireplaces or wood stoves to heat the air.

How A Gas Furnace Works: The Heating Cycle

When a furnace burns a gas, the gas turns into carbon dioxide and water vapor.

The carbon dioxide goes up the chimney while the water vapor becomes steam. The steam heats the air before being expelled back into the room.

How A Gas Furnace Works

Gas furnaces work like this:

  1. Fuel enters the furnace through the burner.
  2. The burner ignites the gas.
  3. The flame heats the metal parts of the furnace.
  4. The metal parts become red hot.
  5. The metal parts release heat into the air.
  6. The heat travels through the ducts and out into the room.
  7. The air circulates through the room until it reaches the return air vent.
  8. The air returns to the furnace where it picks up more heat.
  9. The air leaves the furnace and circulates through the room again.
  10. The cycle repeats itself until the room has reached its desired temperature.

How A Propane Furnace Works: The Propane Heating Cycle

Propane furnaces work like this:

  1. Propane enters the furnace through the tank.
  2. The tank ignites the propane.
  3. The burner heats the metal parts of your furnace.
  4. The metal parts become hot enough to ignite the propane.
  5. The propane burns with the oxygen in the air.
  6. The flames heat the metal parts of the system.
  7. The metal parts become very hot.
  8. The metal parts release the heat into the air. The air circulates around the room until it gets to the return air vent. The air returns to your furnace and picks up more heat. The process continues until you reach your desired temperature.
How Does A Furnace Work?

What Is the Best Type Of Furnace For Your Home?

There are many factors to consider when choosing which type of furnace is best for your home. Below are some things to think about:

  • How much space do you need heated?

You will need to consider the size of your home, and the amount of space that you need to be heated – different furnaces will work best in different spaces.

If you live in an apartment, then you may want to choose a smaller unit. You can also look at installing a wall heater or a portable heater if you don’t have a lot of room.

  • Do you have pets?

If you have pets, you should make sure they won’t get burned by the exhaust from your furnace. Make sure that you install a pet-safe filter on your furnace.

  • Are there any restrictions on how far away the furnace can be placed from an electrical outlet?

Depending on the type of furnace you purchase, you may not be able to place it near an electrical outlet. This could cause problems if you ever need to move the furnace.

  • Is your home located in a cold climate?

Furnaces work better in warmer climates than in colder ones. They typically use less fuel because the air doesn’t have as much moisture in it.

  • Do you want to install a forced-air system, radiant floor system, or hydronic system?

A forced-air system uses fans to blow warm air throughout the house. It works well in homes with large rooms, but it isn’t good for bedrooms.

Radiant floor heating is similar to hydronic systems (see also ‘Everything You Wanted To Know About Hydronic Heating‘), except that it uses pipes to transfer heat from one area to another.

Hydronic systems are great for small apartments and condos, but they aren’t ideal for larger houses.

  • How much money are you willing to spend?

The cost of your new furnace depends on what kind of furnace you choose.

You can find high-quality units for $500-$1000, while lower-priced models sell for under $100. Be sure to shop around before buying so that you get the best deal possible.

  • What will be the cost of installation?

When you buy a furnace, you will probably pay extra to have it installed. Most companies charge between $200-and $300 per hour of labor.

Some companies offer free installation if you buy a certain number of products. Ask your salesperson for details.

  • What is the warranty period?

Most manufacturers offer warranties ranging from 5 years to 20 years. Check with your local dealer to see what their warranty covers.

  • Is there adequate ventilation in your home?

Make sure that your home has enough ventilation. You may want to add a second register to increase the airflow through your home.

  • Will you have access to natural gas, propane, or oil?

Some people prefer using these fuels because they feel more comfortable knowing that they are using clean energy. Others like them because they know exactly where their fuel comes from.

  • Can you afford to replace your current furnace if it breaks down?

It is important to check your budget when purchasing a new furnace. You might be able to save some money by replacing your old furnace now instead of waiting until it fails completely.  

Final Thoughts

Understanding the parts of your furnace, and having a basic idea of how it works, can really help you to make the most of your furnace, and helps to put you in a better position in the event that something goes wrong – you will know where to start when it comes to repairs and maintenance.

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By Anthony Barnes

Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age