By Anne Fonda
A gas furnace is a type of forced air heating system that utilizes natural gas or propane to generate heat. Heated air is then pushed through ductwork and distributed throughout the entire home.
According to the U.S. Energy Information Administration, in 2020, 52% of American households used natural gas for heating, while another 5% use propane gas for heating.
Gas furnaces use an ignition source (such as a hot surface ignitor) to ignite the gas as it leaves the burner assembly. This ignites the fuel, creating combustion which produces heat.
When a furnace burns natural gas or propane fuel, its exhaust/combustion by-products enter and travel through the heat exchanger. The hot flue gas heats the heat exchanger as the gas makes its way to the furnace exhaust outlet. As this occurs, air circulating over the exterior of the heat exchanger picks up the heat.
Then, the blower fan inside the furnace cabinet distributes the heated air through the ductwork until the thermostat registers that the set temperature has been reached. The furnace may then shut off or run at a lower speed to maintain the set temperature, depending on the model.
AFUE stands for Annual Fuel Utilization Efficiency. It’s represented as a percentage. For example, a high-efficiency furnace with an AFUE rating of 97% uses 97% of the fuel burned to heat your home, while the other 3% escapes your home as flue gases. Compare that to a gas furnace with an 80% AFUE rating. 80% of the fuel burned goes to heating your home, while the other 20% is sent out of your exhaust pipe or chimney as flue gas.
Put another way, with a 97% AFUE, 97 cents of every dollar goes into heating your home. With an 80% AFUE, only 80 cents of every dollar goes into heating your home, while the other 20 cents goes up the chimney.
Gas furnaces can be one of the most cost-effective heating systems available today, especially in areas where natural gas rates are substantially lower than electricity rates. Additionally, gas furnaces have longer lifespans than other types of home heating systems, typically lasting anywhere from 20+ years, depending on usage and maintenance.
If you’re concerned about burning fossil fuels to heat your home, but you live in an area with colder winters, you may want to consider a dual-fuel heat pump system. This hybrid heating system pairs a heat pump (standard or cold climate heat pump) with a gas furnace.
The heat pump cools in the summer and heats in the fall and some, or all, of the winter. When the outdoor temperatures drop enough that the heat pump is not operating efficiently, the gas furnace kicks in to heat your home. When temperatures rise, the heat pump takes over again.
“Today’s cold climate heat pumps are engineered to perform reliably in much lower temperatures than traditional systems. Advanced inverter technology allows them to maintain meaningful heating capacity even in single-digit or subzero conditions, giving homeowners in northern climates an efficient alternative to fossil fuel heating.”
– Chelsea Hudson, Product Manager, Heat Pumps
If you’re thinking about furnace replacement, check out some of these resources to help you make an informed decision.
Contact your local Trane HVAC pro to go over your options for heating your home.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Thomas Gort, Senior Furnace Engineer
Annual Fuel Utilization Efficiency (AFUE) measures how efficiently a furnace converts fuel to energy. The higher the AFUE rating, the more efficient the furnace.
A heat exchanger is a critical component in your furnace that transfers heat to provide space heating.
The furnace ignitor and furnace burners are the heart of a forced air heating system. One ignites the fuel while the others heat the air.
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