How long does a furnace last?

Most furnaces last 15 to 20 years. Lennox puts it plainly: "The average lifespan of furnaces is 15-20 years."^[1] An electric furnace often runs longer, and a well-built, well-kept furnace occasionally reaches 30. Where yours lands depends mostly on three things: whether it was sized and installed correctly, how well it has been maintained, and how hard it works. If you bought the house with the furnace in it, you may inherit one that is already well into that range.

Expected lifespan by type

Lennox says gas furnaces can last 15 to 20 years, boilers 15 to 30 years and electric furnaces 20 to 30 years.^[1] Carrier says a well-maintained furnace typically lasts 15 to 20 years,^[2] and that with proper installation, regular maintenance and appropriate use, a high-quality furnace can potentially last up to 30 years.^[2] It explains that electric furnaces can last slightly longer than gas furnaces, often 20 to 30 years, because they have fewer mechanical parts and do not require combustion.^[2]

Bryant adds a note of realism: a furnace can last up to 30 years with excellent maintenance, but most systems begin to lose efficiency and reliability after 15 to 20 years.^[3] Lasting is not the same as working well.

For heat pumps, air conditioners and whole systems, see how long an HVAC system lasts.

What shortens a furnace's life

Wrong size. Bryant explains both sides: "Oversized units turn on and off frequently—a problem known as short cycling—causing excessive wear on the blower motor and heat exchanger."^[3] "Undersized units, by contrast, may run for longer periods while trying to reach the set temperature."^[3] Size is set on installation day, which is why the heating-load calculation matters when you replace one. If a new furnace keeps switching off after a few minutes, read why a new furnace short cycles.

Installation faults. Carrier lists ductwork issues, drainage problems in high-efficiency furnaces, and incorrectly installed fuel lines^[2] among the installation problems that cut lifespan. Lennox adds: "Inaccurately installed venting can also affect performance and reduce furnace lifespan."^[1]

Missed maintenance. Carrier warns that neglect leads to dirty buildup on heat exchangers, burners and fan blades,^[2] which restricts airflow and heat transfer. The filter is the part you can keep clean yourself, and Carrier explains why it counts: "Clogged filters restrict air, forcing the furnace to work harder and longer."^[2] In the worst case, Carrier says a severely clogged filter can result in an overheated and possibly cracked heat exchanger, which can lead to a carbon monoxide leak.^[4]

Hours of use. A furnace in a cold, drafty house runs more than one in a tight, well-insulated house. Carrier points out that the furnace often serves as the air handler for your central air conditioner or heat pump,^[2] so its blower may run all year. Thermostat habits count too: Carrier says consistently setting your thermostat significantly higher forces the system to run more often, which may contribute to additional operating hours and wear.^[2]

What helps a furnace last

Most of what extends a furnace's life is routine, and some of it is yours to do. Carrier suggests that between professional visits, homeowners keep up with replacing air filters every 1-3 months, inspecting and cleaning vents and air return ducts, and ensuring the thermostat is communicating correctly with the system.^[4] It also says to keep the area around the furnace clear of debris,^[4] and Bryant recommends you keep return grilles unobstructed and supply registers open.^[3]

• The filter. Check it monthly and change it on the schedule for its type. See how often to change a furnace filter and what MERV rating to use.
• Registers and returns. Keep furniture and rugs off them, and reopen any you closed for summer.
• Changes you notice. New noises, a burner flame that turns yellow, or a furnace that takes longer to start are reasons to book service, not to wait.

The rest is a yearly professional tune-up. ENERGY STAR suggests you check the heating system in the fall,^[5] before contractors get busy. Its checklist for the visit includes: "Check all gas (or oil) connections, gas pressure, burner combustion and heat exchanger."^[5] Safety agencies say the same. The EPA advises: "Have a trained professional inspect, clean and tune-up central heating system (furnaces, flues and chimneys) annually."^[7] The U.S. Fire Administration says: "Maintain heating equipment and chimneys by having them cleaned and inspected each year by a professional."^[8]

For what a service plan includes and whether one pays off, see are HVAC maintenance plans worth it.

Planning for the end

ENERGY STAR says it may be time to call a professional contractor about replacing a furnace or boiler that is more than 15 years old.^[6] That does not mean pulling out a furnace that runs well. It means getting it inspected, learning what a replacement would cost, and deciding before it fails on a cold night. The signs to watch are in when it is time to replace a furnace.

When to call a licensed pro

Filters, registers and keeping the area clear are homeowner jobs. Everything inside the furnace cabinet, including burners, gas connections, the heat exchanger, venting and controls, is work for a licensed HVAC technician. Under Virginia law, no individual may work as a tradesman without a licence, and the Code's definition of a tradesman includes anyone doing heating, ventilation and air conditioning work for the public for pay.^[9][10] Check a business on DPOR's License Lookup.^[11]

Book service when the furnace has had no tune-up in over a year, when it starts short cycling or making new noises, or when a technician has mentioned the heat exchanger. If you smell gas or have carbon monoxide symptoms, Columbia Gas of Virginia tells its customers to "go outside and call 911" and then call the gas company.^[12]

Getting service in Virginia

Loclis lists DPOR-licensed HVAC businesses with their licence number and class. Look up HVAC businesses in Blacksburg, browse furnace replacement, or read more heating and cooling answers.

Describe your furnace and what it needs and licensed local HVAC businesses quote the tune-up or repair.