8 Signs You Need to Replace Your Furnace (and When to Repair Instead)

Updated October 2026

Most furnaces don't fail without warning. Before a breakdown, they usually show signs: higher bills, odd noises, repairs that keep coming back. Some of these signs mean a part needs fixing. Others mean the furnace is near the end of its life. Here's how to tell the difference, and how to decide whether to repair or replace.

If something already seems wrong, our furnace repair team in Sacramento can inspect your system and give you an honest answer.

8 Signs It May Be Time to Replace Your Furnace

1. Your furnace is 15 or more years old

Most gas furnaces last 15–20 years. Many Sacramento homes built in the 1980s and 1990s still have their original furnace in the attic or garage. Even if it still runs, an older furnace is usually far less efficient than a new one, and parts get harder to find. Past 15 years, it's worth getting a replacement quote before the next breakdown forces a rushed decision.

2. Repairs are getting more frequent

Every furnace needs an occasional repair. But if you've called for service more than once in the last two years, or the same problem keeps returning, the furnace is likely wearing out as a whole rather than one part at a time.

3. Your heating bills keep climbing

Compare this winter's gas bills with the same months last year, allowing for rate changes. If you're paying more for the same comfort, your furnace is probably running longer to do the same job. Worn burners, a failing blower motor or leaky ducts can all cause this.

4. Low efficiency (AFUE) compared with new models

Furnace efficiency is measured as AFUE, the share of fuel that becomes heat. A furnace rated 80% AFUE turns 80 cents of every gas dollar into heat. Older furnaces often ran at 60–70% when new, and efficiency drops further with wear. Today's models range from 80% to 98%. If your furnace is old and inefficient, a new one can pay back part of its cost through lower bills.

5. Yellow flame, soot or rust

A healthy gas burner flame is mostly blue. A yellow or orange flame, soot around the furnace, or rust on the cabinet can mean the furnace isn't burning cleanly. That can produce carbon monoxide. Make sure your CO detectors work, and have the furnace inspected right away.

6. Strange noises

Banging, rattling, squealing or loud booms at startup usually point to a specific problem, like a loose part, a worn belt or delayed ignition. Many can be repaired. On an older furnace, though, noises often show up along with other signs of wear. See why your furnace is so loud for common causes.

7. Uneven heating or rooms that never warm up

If some rooms stay cold or the furnace runs constantly without reaching the set temperature, it may be too small, failing, or held back by duct problems. A technician can tell you whether the fix is in the furnace or the ducts.

8. A cracked heat exchanger

The heat exchanger keeps combustion gases separate from the air you breathe. If a technician finds a crack, the furnace should be shut off. On most furnaces past their warranty, replacing the heat exchanger costs so much that a new furnace makes more sense.

Repair or Replace? The 50% Rule

A simple guideline: if a repair costs half or more of what a new furnace would cost, replacement is usually the better value. This applies especially if the furnace is 15+ years old. Furnace repairs in Sacramento range from a couple of hundred dollars for a part like an ignitor or flame sensor to well over a thousand for major components. A new furnace typically runs $4,500–$11,000 installed, depending on size, efficiency and ductwork. See our furnace installation page for details.

Repair usually makes sense when:

• The furnace is under 10–12 years old
• It's a single, inexpensive part (ignitor, flame sensor, capacitor, thermostat)
• It has been maintained and repairs have been rare

Replacement usually makes sense when:

• The furnace is 15+ years old and needs a major repair
• The heat exchanger is cracked
• Repairs are frequent and bills keep rising
• Your AC is also old, and you could replace both with one heat pump

Consider a Heat Pump When You Replace

If your furnace and air conditioner are both aging, a heat pump can replace both with one system. Sacramento's mild winters suit heat pumps well, and SMUD currently offers rebates of up to $3,000 for switching from a gas furnace. Read our furnace vs. heat pump comparison and check current rebates and tax credits.

Help Your Furnace Last Longer

An annual furnace tune-up catches small problems early and keeps efficiency up. Changing your filter regularly helps too. See how often to change your air filter. Not every warning sign means you need a new furnace. Sometimes a cleaning or a single part is all it takes.

Frequently Asked Questions

How long does a furnace last?

Most gas furnaces last 15–20 years with regular maintenance. Furnaces in hot attics, or ones that skipped annual tune-ups, often wear out sooner.

Is it worth repairing a 20-year-old furnace?

Usually only for a small, inexpensive repair. For anything major, a 20-year-old furnace is generally better replaced, because more repairs are likely and a new unit will cost less to run.

What is a good AFUE rating for a new furnace?

80% AFUE is the standard minimum. High-efficiency condensing furnaces reach 95–98% AFUE and cost more upfront, but they use less gas.

Can a technician tell me if I need a new furnace?

Yes. An inspection checks the heat exchanger, burners, blower, safety controls and efficiency. Ace will tell you plainly whether a repair is worth it or replacement is the better choice.

Get an Honest Repair-or-Replace Answer

Ace Plumbing Heating & Air Conditioning has served Sacramento homeowners since 1972. We'll inspect your furnace, explain what we find, and give you clear options, whether that's a furnace repair or a new system. Schedule an inspection or call (916) 455-4548.