How Does a Furnace Actually Work?

The majority of households in the United States rely on some type of furnace or boiler for heat.  Overall, natural gas furnaces are the most commonly used heating equipment in most parts of the country. The southeastern parts of the country are the exception, where electric furnaces are more common.

As we head into winter, it is a good idea to learn a thing or two about your furnace since these machines will help to ensure your family’s comfort and safety. Understanding how your furnace works will help you troubleshoot your furnace and potentially avoid issues when you need them the least. In a perfect world, your furnace will just does its job quietly and you won’t have to think about it much. If you keep up on the yearly maintenance, your unit should be ready for the winter months and perform at its full potential.

So let’s start with some of the basics.


What Is a Furnace?

A furnace is a device catering to all your heating and radiation purposes. Simply put a furnace helps raise the temperature of the substances and/or provide heat to the spaces subjected to it. A furnace may also refer to clay baking devices known as kilns.

In North American countries like America and Canada, household heating systems or domestic radiators are called furnaces. These heating systems are homogenous distributors of heat in extremely cold weather conditions, using convectional heat produced by central furnaces, or as British call them – boilers, or heaters.

Almost all furnaces direct air throughout a building using a blower, which is why they are called forced-air furnaces. They can use a variety of fuels to create warmth including electricity, oil, coal, liquid propane gas or natural gas. Natural gas forced-air furnaces are the most common type of furnace. Read on to learn the parts of a gas furnace and how they work to create warmth in a building.


Types of Furnaces

Different types of furnaces are generally categorized by the type of fuel used to power the unit. The four most common types of furnaces are gas, propane, electric and oil. In an electric furnace, exposed electric heating elements heat the air. In most other types of furnaces, there is a heat exchanger or special chamber where the air is warmed before it is distributed through the ductwork and vents. The thermostat works with any of these systems to signal the furnace automatically to shut off when the home reaches the desired set temperature.

Let’s take a closer look at the four top types of furnaces:


  • Natural gas furnaces are highly economical. Older gas furnaces are only about 65% efficient on average. Modern gas furnaces can be up to 98% efficient. Natural gas is also the most popular way Americans heat their homes. Nearly half the country currently uses this energy source. However, usage varies widely by region.
  • Oil furnaces are most commonly found in the northeastern United States. They are slightly less efficient than gas furnaces, typically between 80-90%, but the upfront cost is lower. Natural gas furnaces can cost up to 25% more to purchase.
  • Electric furnaces are the most budget-friendly. Some units are nearly half the cost of gas furnaces. They’re also easier to install and typically last up to 10 years longer. The cost of electricity is much higher than gas, so you’ll pay for the difference on your monthly energy bill.
  • Propane is a byproduct of oil and gas production. It’s easily stored in tanks and used by almost 10% of U.S. households. This is a great option if gas and oil aren’t readily accessible in your area.


How a Gas Furnace Works

Let’s look at the heating process:

  1. The furnace’s process to create and distribute heat starts outside the building. This is where the fuel source enters the building from either a liquid propane gas storage tank or a gas supply network. 
  2. The igniter heats up or creates a spark and ignites the burner. 
  3. The gas from the burner creates an even, steady flame.
  4. Cold air from the building enters the furnace.
  5. The burning gas warms the cool air inside the heat exchanger. 
  6. The furnace pipes exhaust out of the building through an exhaust pipe. 
  7. The blower fan pushes the warm air throughout the building. The thermostats tell the system which rooms require heat.
  8. As the warm air circulates around the building, cold air is pulled into the return ducts and directed to the furnace where it can be heated again.
  9. Once the rooms have reached the temperature set on the thermostat, the system signals the furnace to turn off the gas valve so the furnace stops pushing warmed air into the building. 


How a Propane Furnace Works

A propane furnace works largely the same way as a natural gas furnace. They are so similar that an experienced HVAC professional can easily convert a gas furnace to a propane system. The main difference is that the propane fuel must be kept in tanks and refilled regularly, while a gas furnace system is attached to a natural gas line with a constant stream of gas.

One of the benefits of a propane furnace is that burning propane does not emit any greenhouse gases and that you can purchase propane before the higher-demand winter months. However, you must have tanks to store the propane and keep up with regular deliveries to fill the tanks. If your tanks run out of propane, you risk your furnace shutting down completely. You will also need to watch for leaks in the tanks and be more careful during natural disasters, as a tornado or hurricane can cause an explosion with a propane tank.


How an Electric Furnace Works

Have you ever looked into the toaster when it is toasting bread? Much like a toaster, an electric furnace works the same way to heat your home. An electric furnace consists of a cabinet with a blower motor and heating coil attached to it. The heating coils are also referred to as a heat package or heat strips.

When a call for heat comes from the thermostat, an electric current runs through the heating coils, making them extremely hot. As the blower motor inside the furnace pushes air over the heating coils, the air warms up and the temperature inside your home increases. Once the desired temperature is met, the thermostat tells the system to shut down until heat is needed again. 


How an Oil Furnace Works

The heating cycle for an oil-fired furnace begins when the thermostat senses a drop in the temperature and the need to generate heat. This causes the activation of the burner motor that pulls heating oil from a storage tank. The tank may be located aboveground on the inside or outside of your home, or possibly buried underneath the ground. The oil is combined with the appropriate amount of air while an ignition transformer simultaneously generates a spark. The oil breaks up and vaporizes as it passes through a nozzle, which enables it to be ignited by the spark.

After a brief delay to allow the heat exchanger to warm up, the furnace’s blower motor draws in air that is heated as it passes over the heat exchanger. The heated air is then sent through a duct system, which distributes it throughout your home. Once your home reaches the desired temperature, the burner motor is de-energized and the flow of heating oil ceases.


Things to Consider When Choosing a Furnace

A furnace remains one of the best options to consider if you’re planning to install a heating system.

A furnace system can offer a lot of benefits. For one, it is an efficient heating system for your home. The system’s efficiency is denoted by an Annual Fuel Utilization Efficiency (AFUE) rating. The higher the AFUE, the more the furnace system can deliver to the relative amount of consumed fuel.

Typically, standard and natural gas burning furnaces have an AFUE rating of 78 to 84%, but they can go even higher. Additionally, a furnace system is capable of heating your home more rapidly. It has faster start periods and offers comfort to your entire home quickly.

If you plan to decide in investing a furnace system, it’s highly recommended that you research to ensure that you’ll make the most out of your money. So, before you make a purchase, here are some of the most important things that you need to know:


  • Choose the Right Size

It’s essential to have the right size furnace for your home. An HVAC expert will use the size of your home, local climate, ceiling height, and even the number of windows to determine the right size furnace. Contact a qualified local HVAC expert to help you choose the best unit.


  • Compare Furnace Reviews

Do not just go for the cheapest furnace. A lower-priced unit may end up costing more to operate and repair if it runs less efficiently. Check out customer reviews on any furnace you are considering before you buy, and ask an HVAC professional for their opinion. HVAC professionals can often offer insight into the best brand based on your needs. They will also have first-hand experience with repairs or common furnace problems.


  • Climate and Region

Where you live will determine the climate and the availability of energy sources. Gas furnaces are more efficient in some areas while electric furnaces are the best choice in others.


Choose a Trusted Service Company for an Inspection and Tune-Up

If you have discovered a problem with the home’s HVAC system, think about calling a trusted local service company before you decide against buying. They can complete a thorough inspection, determining the extent of existing issues and looking for any others. If the problem can be fixed with a simple tune-up, buying the house may still be worth it.

And there is always a chance the previous owner simply wasn’t aware of the problem. If there is something wrong with the HVAC system, it never hurts to ask if potential replacement costs will be factored into the cost of the home itself. In any case, the more info you have, the better decisions you can make.

You can always count on the Aire-Tech to keep your home cool. Perhaps you need repairs, new thermostat installation, or preventative maintenance—whatever the HVAC issue is, Aire-Tech is ready to help. If your system needs repair or inspection before summer, call us on 951-926-1002. You can also visit our Contact page and complete the contact form.