Repair a furnace or air conditioner when it is mid-life and the repair is modest. Replace it when it is near the end of its published lifespan, the repair is large, or breakdowns keep coming. We give you both prices so you can decide.
Should I repair or replace my furnace?
Repair the furnace if it is under about 15 years old and the repair is a common part such as an igniter, sensor or switch. Replace it if it is near or past 20, the repair is a major part, or it has needed several repairs in a row.
HomeGuide's HVAC repair page suggests considering replacement when a unit is over 10 years old and the repair is more than 30% of a new system. That is a rule of thumb, not a law. Safety comes first: a cracked heat exchanger or a carbon monoxide problem changes the answer.
How long does a furnace last in Michigan?
A furnace lasts 15 to 30 years, by HomeGuide's published figures, and a gas furnace 15 to 25 years. Michigan furnaces run long seasons, so maintenance makes a big difference. A furnace that has had yearly tune-ups often outlasts one that was ignored.
How long does an AC unit last, and what are the signs it is dying?
An air conditioner lasts 15 to 20 years on HomeGuide's AC replacement page, and 12 to 15 years with proper maintenance on its AC repair page. Detroit units run fewer months a year than units in the South, but winter freezing and salt spray from roads still wear outdoor coils.
- It runs longer and cools less than it used to.
- Repairs are getting closer together.
- It needs refrigerant every season, which means a leak.
- The outdoor unit is loud, rattles or hums.
- Your summer electric bill climbs without a reason.
- It uses R-22 refrigerant.
How do I know my furnace needs to be replaced?
Your furnace needs to be replaced when it is unsafe, keeps breaking, or costs more to run and repair than it is worth. Warning signs include a cracked heat exchanger, rust and soot around the burners, repeated carbon monoxide alarms, rooms that never warm up, and repairs every winter.
Rising gas bills on a 15-year-old or older system are another sign, especially if the house has not changed. A new high-efficiency furnace will not fix leaky ducts or a drafty house, though, so we check those too.
My 15 to 20 year old furnace needs an expensive repair. Fix it or replace it?
For a 15 to 20 year old furnace, a repair costing hundreds of dollars or more usually points to replacement, unless the furnace has been well kept and the part is the only problem. At that age, other parts are close behind. Paying for a big repair now and a new furnace two winters later is the common bad outcome.
A worked example: an 18-year-old furnace needs a new inducer motor. The part is in HomeGuide's $400 to $1,100 range. If the heat exchanger is sound and the furnace has had tune-ups, the repair can be reasonable. If it also has rust, a weak blower and high bills, we would show you the replacement price too.
My 15 year old AC keeps freezing up. Is it worth repairing?
An AC that keeps freezing up usually has low refrigerant from a leak, a dirty coil or poor airflow. If the cause is a filter or a blower problem, it is worth fixing. If it is a refrigerant leak on a 15-year-old unit, replacement often makes more sense, because the leak tends to come back.
The technician says my heat exchanger is cracked. Do I really need a new furnace?
If the heat exchanger is truly cracked, yes, in most cases, because a crack can let combustion gases into your air. Ask the technician to show you the crack with a camera or photos and to explain the carbon monoxide test results.
A cracked heat exchanger is also a known upsell line. A second opinion is reasonable, and a good contractor will not mind. Do not run the furnace while you wait if carbon monoxide was found.
My AC uses R-22. Do I have to replace the whole thing?
No, you do not have to replace an R-22 system just because of the refrigerant, but a major leak usually makes replacement the better choice. R-22 production has been banned since 2020, so recharging uses the remaining supply. HomeGuide lists R-22 at $90 to $150 a pound installed, against $50 to $80 for R-410A.
An R-22 unit is at least 15 years old, so it is near the end of its life anyway. A small repair on a unit that holds its charge can still make sense.
Should I replace a working AC when I replace the furnace?
Replacing them at the same time makes sense when the AC is over about 12 years old or uses R-22. Then the coil can be matched to the new outdoor unit and the job is done in one visit. If the AC is under 10 years old and works well, keep it and have the coil checked.
What is the 5,000 rule for HVAC replacement?
The 5,000 rule is a rule of thumb: multiply the age of the unit in years by the repair cost in dollars. If the result is over 5,000, it suggests replacing. A 12-year-old AC with a $500 repair gives 6,000, which points to replacement.
It is a quick guide, not a published standard, and it ignores safety, efficiency and how well the unit was kept. Use it to start the conversation, not to end it.
The only way to get a real price for your home is an on-site visit and a written quote. Call or text (313) 488-2188.