Buying & hiring
Repair or replace: the age-times-cost rule and what it misses
Multiply the age by the repair cost. Over 5,000, lean towards replacing. It is a good start, and here is what it leaves out.
The rule of thumb
The most quoted rule in the trade multiplies the equipment’s age in years by the repair cost in dollars. If the result is over 5,000, replacing is usually the better choice; under it, repair. A $300 repair on a 10-year-old unit gives 3,000, so repair; a $1,500 repair on a 12-year-old unit gives 18,000, so replace. The rule captures two things at once: older equipment has less life left to spread the repair over, and expensive repairs are a large share of a replacement.
Typical lifespans
The HVAC lifespan and replacement planner uses these typical service lives, from ASHRAE equipment service-life data and DOE and ENERGY STAR guidance:
| Equipment | Typical life | Median |
|---|---|---|
| Central air conditioner | 12 to 20 years | 15 |
| Air-source heat pump | 10 to 18 years | 15 |
| Gas furnace | 15 to 25 years | 18 |
| Boiler | 20 to 35 years | 25 |
| Ductless mini-split | 12 to 22 years | 17 |
| Tank water heater | 8 to 15 years | 11 |
| Tankless water heater | 15 to 25 years | 20 |
Coastal salt air, heavy use and lack of maintenance shorten them; yearly maintenance lengthens them. A heat pump works year-round, which is why its life is a little shorter than an air conditioner’s.
Common repair costs
The AC repair cost calculator uses ranges from Fixr and This Old House:
| Repair | Typical range |
|---|---|
| Capacitor | $100 to $400 |
| Contactor or relay | $150 to $450 |
| Condenser fan motor | $300 to $800 |
| Control board | $200 to $800 |
| Refrigerant leak repair and recharge | $200 to $1,600 |
| Indoor blower motor | $450 to $2,000 |
| Evaporator coil | $1,000 to $2,500 |
| Compressor | $1,000 to $3,000 |
Two repairs, two answers
A capacitor on a 12-year-old 3-ton air conditioner:
- Repair midpoint: $250
- Age × cost: 12 × 250 = 3,000, under 5,000
- Share of a new air conditioner’s midpoint of $5,550: 5%
- Verdict: repair
A compressor on a 14-year-old unit:
- Repair midpoint: $2,000
- Age × cost: 14 × 2,000 = 28,000, well over 5,000
- Share of a new air conditioner: 36%
- Verdict: lean towards replacing
What the rule misses
Refrigerant. Units built before 2010 use R-22, no longer produced in the US, so recharging one is expensive and getting more so. Since 2025 new systems have moved to A2L refrigerants such as R-454B and R-32. A leak on an R-22 unit tips the decision towards replacement; on an R-410A unit it may still be worth repairing.
Efficiency. A 15-year-old air conditioner at SEER 10 uses far more electricity than a new one. Replacing it with a SEER2 15.2 unit saves about $290 a year on a 3-ton system at 1,200 full-load hours and 17 cents, from the guide to efficiency ratings. Over the years that difference can pay for much of the gap between repairing and replacing.
The rest of the system. Replacing an outdoor unit without its matched indoor coil often costs most of a full replacement and leaves a mismatched system. A 20-year-old furnace with a new air conditioner may be the next failure.
Repair history. A unit that has needed several repairs in two years is likely to need more. The planner adds recent repairs to the current quote before applying the rule.
Safety. A cracked furnace heat exchanger is a carbon monoxide risk and a reason to replace, whatever the rule says.
Timing. Replacing in spring or autumn, before the system fails, gives time for quotes and avoids emergency prices. A unit inside its replacement window is worth budgeting for even if it works.
A 20-year-old furnace with a repair quote
A gas furnace installed in November 2006, maintained yearly, $1,400 of repairs in two years, and a current quote of $900.
- Age: 19.9 years; adjusted typical life 17 to 28 years, median 20
- Age × repair: 19.9 × 900 = 17,906, over 5,000
- Verdict: replace rather than repair
Questions to ask the technician
Before deciding, get the facts the rule needs and the ones it leaves out:
- What exactly failed, and why? A capacitor that failed from age is a one-off; a compressor that failed because of a refrigerant leak may fail again if the leak is not found.
- What refrigerant does the system use? R-22 tips the decision towards replacing; R-410A and the newer A2L refrigerants do not.
- What condition are the other parts in? Ask specifically about the indoor coil, the blower motor and, for a furnace, the heat exchanger.
- Is the part under warranty? Many manufacturers cover compressors for 10 years if the unit was registered, which can turn an expensive repair into a labour-only bill.
- How long is the repair warranted? A 90-day labour warranty on a major repair to an old unit is a sign the technician expects more trouble.
Write down the answers. They feed the planner and make replacement quotes easier to compare.
Maintenance and the decision
Regular maintenance extends equipment life and catches failing parts while they are cheap to replace. The HVAC maintenance cost calculator compares paying per visit with a service plan: for a furnace and an air conditioner with one tune-up each a year at $250, $60 of filters and $200 of expected repairs, a $300 plan with 15% off repairs comes out $230 a year cheaper.
When you decide to replace
Use the HVAC system replacement cost calculator to set a budget and the guide to what HVAC installations cost for the sourced ranges. Size the new system from a load calculation rather than the old nameplate, and read quotes with the guide to reading an HVAC quote.