How does a gas furnace work?

Your guide to gas furnaces

If you’ve ever wondered “How does a gas furnace work?”, you’re in the right place. Your Albuquerque heating services experts are here to answer your questions about these systems and explain how gas furnaces work, what gas furnace components you need to know about, and more.

In this article, we’ll also explore how gas furnaces heat your home, what makes a gas furnace more (or less) efficient than another, and whether or not gas furnaces are better than electric ones. It’s time to talk about furnaces.

How do gas furnaces work?

The basic premise behind gas furnaces is the creation of heat energy through combustion. Natural gas is the fuel that gets combusted. As heat is generated, it’s then pushed out into your home through your air ducts by a device called the blower fan.

You’ve probably heard of “combustion” before in a different context: your car. Your vehicle features an internal combustion engine. Similar to your furnace, it combusts fuel (in this case, gasoline) to generate heat energy. Of course, your car doesn’t really want heat energy as the main outcome—it instead uses that energy to push pistons.

In both your vehicle and in your gas furnace, the combustion process produces exhaust. That’s why your gas furnace has something called a heat exchanger. Basically, it works like this: the combustion process within your furnace happens in a sealed chamber—the heat exchanger.

The heat generated warms up the heat exchanger, which then “exchanges” that heat energy to the other side. All that time, the air inside your furnace and the air inside your home never come into contact. The combustion exhaust is then safely vented out of your home through the flue pipe.

With the heat exchanger warmed up, the blower fan kicks on. It pulls in cold air from inside your home through the return register and then pushes it over the hot heat exchanger. As the cold air passes over it, it’s heated up. This cycle continues until the air in your home reaches the temperature you’ve set on your thermostat.

Wagner: Your gas furnace experts

Watch our video below to learn more about how your furnace operates.

Gas furnace components

Your gas furnace features the following components:

Temperature Control / Thermostat: Working in tandem, your home’s thermostat and the furnace’s temperature control tell the system when it needs to turn on and start generating heat.

Gas Burners: These burners have valves that release gas into the combustion process as more heat is needed in your home.

Ignition Switch: This is what actually combusts the gas, creating a flame and releasing heat energy to be absorbed by the heat exchanger. If your furnace isn’t turning on when you set the thermostat, it could be an issue with the ignition switch—you’ll need to contact us for furnace repair.

Heat Exchanger: As described above, the heat exchanger is designed to be heated up so that cold air can be pushed over it, warming the air in your home. By the way, if you ever smell gas when your furnace is running, it could be because of a cracked heat exchanger. Turn off your furnace and call us right away.

Blower Fan: This fan pulls cold air from inside your home and pushes it over the heat exchanger, rapidly warming that air.

Flue: Also known as an exhaust, this pipe connects to the furnace and runs to the outside, carrying exhaust gases in it.

What makes a gas furnace efficient?

While all gas furnaces operate in the same way, some are far more efficient than others. Let’s start by talking about Annual Fuel Utilization Efficiency (AFUE). AFUE is used to measure how efficient one furnace is compared to another.

You can use a furnace’s AFUE rating to evaluate whether or not it’s more or less efficient than another gas furnace. This distinction is important: for reasons we’ll explain below, electric furnaces often have higher AFUE scores, but that doesn’t always mean you’re getting a great value.

Currently, the minimum efficiency standard for new furnaces in the United States is 80%. High-efficiency gas furnaces can reach up to 98.5% AFUE. Here are just some of the ways a furnace can be more efficient:

Variable-Speed Heating: These furnaces can run at different speeds, allowing them to “shift” up or down in speed depending on how much heat is needed at any given time. This means they can run more efficiently and better maintain a consistent temperature in the home.

Dual Heat Exchangers: Some high-efficiency models feature two heat exchangers, which means that generated heat is distributed faster into the home. This means the furnace ends up running for less time, saving you money.

Smart Controls: When paired with a smart thermostat, high-efficiency furnaces can strategically preheat the home to optimize comfort and reduce the amount of time the system has to run and the amount of fuel it ultimately has to use.

Over the entire life of the system, your furnace’s efficiency really makes a difference. A 10% difference in AFUE can equate to hundreds or even thousands of dollars. It’s important to keep that in mind when shopping for furnaces: energy-efficient furnaces might cost more upfront, but you’ll end up saving that and then some over the next 15-20 years.

What makes gas furnaces different from electric ones?

Gas versus electric furnaces: it’s a question that has confused homeowners for many years. From the names alone, you can probably infer that gas furnaces use gas and electric furnaces use electricity. But, the differences between the two types of furnaces actually go far further than that.

Unlike gas furnaces, electric furnaces do not use combustion—the combination of fuel and flame—to generate heat. Instead, they create heat energy by running electricity through wiring, turning that wiring red-hot and releasing heat energy in the process.

From there, the blower fan pushes that heated air into your home. Picture a supersized version of a toaster, and you’ve probably got a good idea of how an electric furnace works—no toast included, of course!

Are gas furnaces less expensive to operate than electric models? The answer is somewhat complex: while gas furnaces are technically less efficient than electric furnaces, natural gas is often cheaper than electricity.

In most cases, gas furnaces come out ahead. Of course, that’s only if you already have a natural gas connection—if you don’t have a gas hookup at your home, you’ll either need to add one or stick with an electric model.

Get a new furnace installed by Wagner

At Wagner, we install new gas furnaces here in Albuquerque. We’re proud to be a Carrier Temperature Tough Gold Dealer. For decades, Carrier has been known for their high-quality, high-efficiency gas furnaces.

If you’re looking for a new heating system for your home, contact our team for a free in-home estimate. We’ll go over your options, answer your questions, and help find the right system for your home.

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