How long does a furnace last?

By Dana Whitlock. Updated October 2026.

A furnace rarely dies all at once. It wears down part by part. The Department of Energy's 2023 furnace rule analysis uses an average lifetime of about 21.4 years for standard indoor gas furnaces, with sensitivity cases from 16 to 27 years, and notes that the average equals the median in its model. Other industry charts land nearby: 18 years for warm-air gas furnaces in a 2007 builders' study (with oil at 20 and electric at 15), and 15 to 25 years on inspector charts. For most homes, 15 to 25 years is the realistic window. Furnaces in mild climates that run few hours a year tend to outlast those in cold regions. Two parts drive the replace decision. The heat exchanger keeps combustion gases out of your air, and the blower and draft motors run every single cycle.

What wears out

The heat exchanger

The heat exchanger is the sealed metal chamber that passes heat from the burner to your house air while keeping combustion gases, including carbon monoxide, out of it. Lennox explains that years of heating and cooling cycles fatigue the metal, and that dirty filters, restricted airflow and short cycling add stress. Inspector charts give heat exchangers 10 to 15 years, shorter than the furnace as a whole. A crack is a safety problem first and a repair question second.

Inducer (draft) motor

Most modern furnaces use a small draft fan to pull combustion gases through the heat exchanger and push them out the vent. Its bearings wear, and a failing inducer often announces itself with a whine or rattle at startup. If it can't prove draft, the furnace won't light.

Blower motor

The blower moves house air across the heat exchanger and through the ducts, and it often runs for cooling as well. Bearing wear, dirty wheels and failed motors are common age-related repairs.

Ignition and flame sensing

Hot surface igniters crack, and flame sensors get coated and stop proving flame, which causes the furnace to light and then shut off. These are routine repairs, and like all burner and gas-side work they belong to a licensed HVAC technician.

Control board and venting

Circuit boards fail with age and power surges. Vent pipes can separate or corrode, and condensing furnaces have drain lines and traps that clog. Each can stop the furnace or create a safety issue.

Signs it's near the end

• Your CO alarm sounds. Leave the house and call the gas utility or 911 from outside.
• Soot or scorch marks around the burner area or vent connections.
• Rust or corrosion on the furnace cabinet or vent pipe.
• The furnace lights, then shuts off after a few seconds, over and over.
• New whining, grinding or rattling at startup.
• Rooms that won't get warm, or heating bills climbing with no change in use.
• Repairs needed every season, or an age past about 20 years.

What helps it last

• Change or clean the air filter on schedule. A dirty filter overheats the heat exchanger, which Lennox lists as a cause of cracks.
• Keep supply and return registers open and unblocked by furniture or rugs.
• Schedule a yearly tune-up with a licensed HVAC technician, including a combustion and heat exchanger check.
• Keep the furnace area clear of stored items, paint and cleaning chemicals.
• Install CO alarms on every level and outside sleeping areas, as CPSC advises, and test them.
• On high-efficiency furnaces, look for water around the unit, which can mean a clogged condensate drain.

Repair or replace?

Safety comes first. If a technician finds a cracked heat exchanger, the furnace should not run, and on most furnaces past warranty a new furnace makes more sense than a new exchanger. Ask to see the evidence, such as a camera image or combustion readings, and get a second opinion if you have doubts. For other repairs, think in cost per remaining year. Divide the repair cost by the years the furnace can reasonably keep going, using DOE's average of about 21 years as a guide, and compare that with the replacement cost above divided by roughly 20 years of new service. Motors, igniters and boards on a furnace under 15 years old usually pass that test easily. For a quick check, use the 50 percent rule. A repair costing more than about half a new installed furnace, on a unit past 15 years, usually tips the decision to replacement.

Common symptoms

• Why is my furnace blowing cold air
• Why is my furnace leaking water
• Why is my furnace making a loud noise
• Why does my furnace keep turning on and off
• Why won't my furnace ignite