Home & Appliances

How Long Does a Furnace Last?

Gas furnaces last 15–30 years, averaging 17–20 years. Electric furnaces can last 20–30 years. Annual tune-ups are the single most important maintenance task.

15–30 years

Quick Facts

Average Lifespan

15–30 years

Replacement Cost

$3,500–$5,500

Source

InterNACHI, NAHB

Overview

A gas furnace is a long-lived appliance — InterNACHI and NAHB data show an average lifespan of 17–20 years, with well-maintained units reaching 25–30 years. Electric furnaces tend to last even longer, with fewer combustion-related failure modes. Unlike HVAC systems in warm climates, furnaces in cold-climate homes have a clear usage ceiling: they only run in winter. The heat exchanger is the most critical component — a cracked heat exchanger can leak carbon monoxide into living spaces, making it a safety issue that always warrants immediate attention.

Signs It Is Time to Replace

Yellow or flickering pilot light instead of steady blue flame — combustion problem
Increased heating bills without change in weather or thermostat settings
Rooms heating unevenly or taking longer than usual to reach temperature
Unusual smells — rotten egg odor means gas leak; burning smell may indicate overheating
Popping, banging, or rattling sounds when the burner ignites
Cracks or rust visible on the heat exchanger during inspection
Age over 18 years with any mechanical problem

How to Make It Last Longer

Schedule an annual tune-up before heating season — a technician will clean the burners and check the heat exchanger
Replace air filters every 1–3 months — a clogged filter forces the blower motor to work harder
Keep the area around the furnace clear of combustible materials
Test your CO detector annually — a cracked heat exchanger can leak odorless carbon monoxide
Check the flue pipe connections annually for rust, gaps, or disconnection
Bleed radiators if you have a hot water (hydronic) heating system — air pockets reduce efficiency

What Affects Replacement Cost

Furnace size (BTU output) — sized to your home's heat load calculation
AFUE efficiency rating — 80% vs. 96% efficiency models differ by $500–$1,500 upfront
Single-stage vs. variable-speed modulating — variable-speed lasts longer and is more efficient
Gas line and venting upgrades — high-efficiency furnaces require new PVC venting
Regional labor costs and permit requirements

When to Replace

Replace your furnace when the heat exchanger is cracked (a safety issue, not a financial decision — replace immediately), when the unit is over 18 years old and needs any major repair, or when repair costs exceed $1,200 on an older unit. A new 96 AFUE furnace in a cold climate will save $150–$400/year in gas costs compared to an 80 AFUE unit — the payback period is typically 5–8 years.

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Pro Tip

The heat exchanger crack test is something most homeowners never think about. During your annual furnace tune-up, ask the technician specifically to inspect the heat exchanger — not just the burners. A cracked heat exchanger in a basement furnace is the most common source of chronic low-level carbon monoxide exposure in homes. CO poisoning at low levels mimics flu symptoms: headache, fatigue, mild nausea.

Frequently Asked Questions

How long does a gas furnace last?+

A gas furnace typically lasts 15–30 years with an average of 17–20 years per InterNACHI. Annual maintenance is the single biggest factor in reaching the upper end of this range. Units that have never been serviced routinely fail at 12–15 years.

What is the average cost to replace a furnace?+

Furnace replacement costs $3,500–$5,500 installed for most homes. High-efficiency (96 AFUE) units are $500–$1,500 more than standard 80 AFUE units but save meaningfully on annual gas costs in cold climates.