Furnaces

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A furnace heats the home by burning gas or using electric elements, then moving warm air through ducts. Furnaces commonly last 15 to 20 years, depending on type and maintenance.

Draft. Some reference links and cost figures are still being verified.

A furnace heats the home by burning gas or using electric resistance elements, then moving warm air through ducts with a blower. Most furnaces run 15 to 20 years, depending on type, climate, and maintenance.

Quick facts
Question	Short answer
How long does a furnace last?	DOE's Energy Saver guide lists a typical central system at 15 to 20 years. Building America field work found older gas furnaces kept their rated performance across an average life of about 19 years.
When should I consider replacing it?	DOE's guidance suggests replacing a system that is broken, very inefficient, or more than 15 years old, and says to replace when repairs cost more than half the replacement cost.
What does it cost?	A 2026 Angi estimate puts replacing a furnace and AC together at about $7,500 on average. Census-based medians put a furnace alone at about $5,720.
When do I need a pro?	Any gas, venting, combustion, or electrical work, and any sign of carbon monoxide.

How it works

Gas furnaces burn fuel in a sealed burner and pass the heat through a heat exchanger, keeping combustion gases separate from the air in the home. Exhaust vents outdoors. Electric furnaces use resistance elements instead of a burner. A blower moves air across the heat source and through the duct system, and a thermostat calls for heat. Safety switches shut the system down when a fault is detected.

Types compared

Furnace types
Type	How it heats	Efficiency reference	Best fit	Tradeoffs
Standard-efficiency gas	Burner and heat exchanger	Older units are often in the 60s to 80s AFUE range	Homes with existing gas venting	Lower efficiency; flue venting
High-efficiency gas (condensing)	Burner with a second heat exchanger that recovers heat from exhaust	DOE's 2023 rule sets a 95 percent AFUE minimum for non-weatherized gas furnaces, with a compliance date to confirm on energy.gov	Cold climates with gas service	Needs condensate drain and proper venting
Electric resistance	Heating elements warm the air	Efficiency close to 100 percent at the point of use; cost depends on electricity rates	Homes without gas service	Higher operating cost in many regions

Warning signs

Symptoms and next steps
Symptom	Possible cause	Next step
Yellow or flickering burner flame	Incomplete combustion or a dirty burner	Turn the system off and call a licensed technician
Soot near the vent or heat exchanger	Venting or combustion problem	Turn off the furnace and call a technician immediately
Frequent cycling or rumbling	Dirty filter, failing parts, or an oversized unit	Check the filter first, then call a technician
Rising energy bills	Declining efficiency or duct leaks	Schedule a maintenance visit
Carbon monoxide alarm sounds	Possible CO leak	Leave the home, call 911 or the fire department, and do not reenter until cleared

Carbon monoxide safety

Carbon monoxide is odorless and can come from a malfunctioning furnace. Alarm manufacturers generally advise placing detectors near each separate sleeping area and on each level of the home. Follow the manual for your alarm, and test and replace it on the manufacturer's schedule.

Maintenance

Routine maintenance
Task	How often	Who
Replace or clean the filter	ENERGY STAR advises checking monthly and replacing at least every three months; DOE recommends monthly during peak seasons	Homeowner
Keep the area around the unit clear	Ongoing	Homeowner
Professional tune-up	Once a year, ideally before the heating season (DOE and ENERGY STAR both advise annual service)	Licensed HVAC technician
Test carbon monoxide alarms	Monthly, per manufacturer	Homeowner

DIY or call a pro

Common tasks
Task	Homeowner?	Notes
Replace the filter	Yes	Match the size and rating the manufacturer specifies
Check the thermostat and clear vents	Yes	Open supply and return registers and keep them unblocked
Burner, heat exchanger, venting, or gas connection	No	Licensed technician
Electrical components or control board	No	Licensed technician

Codes and permits

Replacement typically needs permits for gas, electrical, and venting work, and the combustion air and venting must match the appliance's requirements.
The International Mechanical Code and the International Fuel Gas Code govern much of this work. Local adoption and amendments control.
DOE's 2023 furnace rule raises the gas furnace minimum to 95 percent AFUE. Confirm the compliance date on energy.gov before buying.

Cost

2026 cost ranges
Job	Typical range	Notes
Furnace alone	About $5,720 (Census-based median)	Varies by type, size, and venting work
Furnace and AC together	About $7,500 on average, range $5,000 to $12,500 (Angi)	Ductwork and electrical upgrades add to the total

These are estimates from published sources. Get at least three written quotes that name the model, efficiency, and included work.

Regional notes

How conditions change the advice
Condition	What changes	Advice
Cold climates	Furnaces carry most of the heating load	Service before the heating season and keep a backup plan for outages
Mild climates	Furnaces run less and often last longer; heat pumps may be the main heat source	Compare furnace and heat pump options by total cost
Flood-prone areas	Water can damage controls and electrical components	Ask a technician to inspect after flooding before restarting

Frequently asked questions

Is my furnace too old to keep running?

Age alone does not decide it. A furnace near 15 years old that runs safely may still be worth keeping, but DOE suggests replacement when repairs cost more than half of replacement.

How do I know if my furnace is safe?

Have a technician inspect the burner, heat exchanger, venting, and combustion air. Keep carbon monoxide alarms installed and tested.

Can I keep the furnace and add a heat pump?

Some homes run a dual-fuel system, pairing a heat pump with a gas furnace. A technician must size and control both to work together.

Hiring checklist

Confirm the technician is licensed for gas work where required.
Ask for a load calculation (Manual J) and an equipment sizing report, not just a rule-of-thumb size.
Confirm the permit, venting plan, and warranty on parts and labor.
Ask for the AFUE rating and what it means for your home's energy use.

Glossary

Terms
Term	Meaning
AFUE (Annual Fuel Utilization Efficiency)	The percentage of fuel converted to heat over a year. Higher means more efficient.
Heat exchanger	The metal part that transfers burner heat into the air stream without mixing combustion gases with indoor air
Manual J	A load calculation that estimates the heating and cooling a home needs
Condensate	Water produced by high-efficiency furnaces that must drain away

Sources reviewed November 4, 2026. Independent professional review: pending. Confirm local rules with your building department.

Repair

Repair services
Service	When you need it	Typical cost (2026 guides)	DIY or pro	Permit usually?
Flame sensor cleaning or replacement	Furnace starts, then shuts off	Cleaning is often the cheapest fix; replacement about $150 to $250 (HomeAdvisor range via secondary sources)	Homeowner can clean with the power off; technician for replacement	No
Igniter replacement	Furnace does not ignite	About $150 to $350 with parts and labor (contractor guides)	Licensed HVAC technician	Usually not
Blower motor repair or replacement	Weak airflow or noise from the blower	Repair about $250 to $900; full replacement can exceed $1,000 (contractor guides)	Licensed HVAC technician	Usually not
Diagnostic visit	Any repair call	Often $75 to $150 (contractor guides), often credited toward the repair	Licensed HVAC technician	No

Maintenance

Maintenance services
Service	When you need it	Typical cost (2026 guides)	DIY or pro	Permit usually?
Annual furnace tune-up	Once a year before the heating season	About $80 to $200; national average near $130 (contractor guides)	Licensed HVAC technician	No
Filter replacement	Monthly checks; replace at least every three months (ENERGY STAR)	Parts cost only; homeowner task	Homeowner	No
Carbon monoxide alarm test and replacement	Monthly test; replace per manufacturer	Low cost; homeowner task	Homeowner	No

Installation

Installation services
Service	When you need it	Typical cost (2026 guides)	DIY or pro	Permit usually?
Furnace replacement	Repairs cost more than half replacement, or the furnace is near end of life	About $5,720 for the furnace alone (Census-based median); see the Cost table	Licensed HVAC technician	Usually yes
Furnace and AC replacement together	Both systems are aging	About $7,500 on average, range $5,000 to $12,500 (Angi 2026)	Licensed HVAC technician	Usually yes

References

Categories: Heating and cooling (HVAC)