There is no single rule, but the U.S. Department of Energy suggests considering replacement if your furnace or boiler is more than 15 years old, needs frequent repairs while energy bills rise, or leaves some rooms too hot or cold. Get a licensed technician's diagnosis and a written quote, and compare it with the cost and efficiency (AFUE) of a new unit.
DOE signs it may be time to replace
From the DOE Energy Saver guide, consider replacing your heating system if:
| Sign | Why it matters |
|---|---|
| Furnace or boiler more than 15 years old | Older equipment may be less efficient |
| Frequent repairs and rising energy bills | Ongoing costs add up |
| Some rooms too hot or too cold | Possible system or duct issues |
| Humidity problems or excessive dust | Comfort and air quality issues |
| Noisy heating or cooling system | Possible mechanical wear |
Things to compare
- AFUE: DOE suggests asking for high annual fuel utilization efficiency (AFUE) when replacing. ENERGY STAR lists certified furnaces.
- The fault: some codes point to inexpensive parts (filters, sensors), others to boards, motors or the heat exchanger. Your code page lists the likely causes.
- Safety findings: a technician may find a cracked heat exchanger or venting problem. ENERGY STAR notes a cracked heat exchanger can cause the equipment to operate less safely.
Before deciding
Ask for the diagnosis in writing, including which part failed and why. Regular maintenance helps too: ENERGY STAR recommends a heating check-up each fall.
Safety first: If you smell gas, don’t touch light switches or use a phone inside. Leave the building and call your gas utility from outside. Turn off power to the furnace before opening any panel, and never bypass or jumper a safety switch. Gas, venting, wiring and control-board work is for a licensed HVAC technician.
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How long do furnaces last?
We do not publish a lifespan figure. DOE suggests considering replacement when a furnace is more than 15 years old, along with other signs like frequent repairs.
What is AFUE?
Annual fuel utilization efficiency, a measure of heating equipment efficiency. DOE recommends looking for high AFUE models when buying.