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How long does a furnace last, and how to tell how old yours is

Most gas furnaces last 15 to 20 years, and a well kept one can reach 25. The serial number on the rating plate tells you how old yours is. The age plus a few warning signs tell you whether to repair it or start planning the replacement.

Updated October 20, 20266 min read

How long heating equipment lasts

Type	Typical life	What usually ends it
Gas forced air furnace	15 to 20 years, up to 25	A cracked heat exchanger or a worn blower motor and controls.
Heat pump	10 to 15 years	It heats and cools, so the compressor runs most of the year.
Hot water or steam boiler	Up to 40 years	The vessel outlasts the burner and controls, which are replaced along the way.
Central air conditioner (for comparison)	7 to 15 years	Often replaced with an old furnace so the two match.

Ranges from the InterNACHI life expectancy chart and the Building Intelligence Center, which puts the industry average design life of forced air furnaces at 15 to 20 years. Yearly service and clean filters push a furnace toward the top of the range.

How to find the age of your furnace

Look for the rating plate, a sticker with the model and serial number, inside the lower door of the furnace or on the side of the cabinet. Some plates print the manufacture date. Otherwise the date is coded in the serial number:

Carrier, Bryant, Payne and Day and Night (since 1980): the first four digits are the week, then the year. A serial starting 4006 was made in week 40 of 2006.
Trane and American Standard (since 2010): the first two digits are the year and the next two the week, so 1316 is week 16 of 2013. From 2002 to 2009 the first digit is the year.
Goodman, Amana and Janitrol (ten character serials): the first two digits are the year and the next two the month. 1903 means March 2019.
Lennox, Armstrong Air, Ducane and Concord (since 1973): the first two digits are a factory code and the third and fourth are the year. 5808 means 2008.
Rheem and Ruud: Rheem’s how old is my equipment page decodes the serial.
Any brand: photograph the plate and the Housemap label scan reads the brand, model and serial and works out the age for you.

Signs a furnace is near the end

It is past 15 years old and needs a major part: a heat exchanger, a control board or a blower motor.
It needs a repair every winter, and the bills keep growing.
Rooms heat unevenly, or it runs and runs without reaching the set temperature.
Heating bills climb while your use and the weather stay about the same.
Loud banging, rattling or squealing from the cabinet.
A yellow, flickering burner flame instead of a steady blue one, soot around the burner, or a carbon monoxide alarm. Turn it off, get everyone outside if the alarm sounds, and call for help the same day.

Repair or replace

Start with the age. A furnace under about ten years old with a failed igniter, flame sensor or capacitor is a repair. A furnace past fifteen with a cracked heat exchanger is a replacement: a crack can let combustion gases into the air you breathe, and the part is a large share of the cost of a new unit.

Then look at efficiency. Older furnaces and boilers run at 56 to 70 percent efficiency, according to the U.S. Department of Energy, while modern ones reach up to 98.5 percent. On an old unit, a large part of every heating bill goes up the flue.

If you can, replace before it fails. A furnace bought in a January emergency is bought in a hurry, without a second quote. Late spring and early fall are when installers have time.

How to make a furnace last longer

Check the filter every month and change it when it looks grey; ENERGY STAR says a dirty filter can damage the equipment and lead to early failure. See how often to change a furnace filter.
Have it checked every fall before the heating season, as ENERGY STAR and the U.S. Fire Administration recommend.
Keep supply and return vents open and clear of furniture and rugs, so the blower is not starved of air.
Keep anything that can burn at least 3 feet from the furnace and other heat sources (U.S. Fire Administration).
On a high efficiency furnace, keep the plastic intake and exhaust pipes outside clear of snow and leaves.

Keep the dates

Write down the install year, the model and serial, and each service date. That record tells a technician what they are looking at, and tells a buyer the furnace was cared for. Housemap keeps it on the furnace card in your house file, next to the water heater and the rest of the equipment, and it feeds the home maintenance budget.

Questions

How long does a furnace last?

A gas furnace usually lasts 15 to 20 years, and up to about 25 with yearly service and regular filter changes. Heat pumps last about 10 to 15 years and boilers can last 40.

How can I tell how old my furnace is?

Find the rating plate inside the lower door or on the side of the cabinet. The date is usually coded in the first four characters of the serial number: week then year for Carrier and Bryant, year then month for Goodman, year then week for Trane since 2010, and the third and fourth digits for Lennox.

Should I replace a 20 year old furnace that still works?

Not automatically. Have it inspected. If the heat exchanger is sound and it runs safely, start budgeting and planning rather than rushing. If it needs a major part, replacing usually makes more sense than repairing.

What shortens the life of a furnace?

Dirty filters, skipped service, blocked vents, a furnace too large for the house that turns on and off in short cycles, and a damp basement that rusts the cabinet.

When is the best time to replace a furnace?

Late spring or early fall, before you need the heat and while installers have time. Replacing before it fails lets you compare quotes.

Sources

Scan the label. Know the age.

Photograph the furnace rating plate and Housemap reads the brand, model and serial, works out the age, checks for recalls and keeps the service dates. Free.

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