Repair when the system is under about 10 years old and needs one part. Replace when it is past 15 and facing a major repair, or when any repair would cost more than half of a new system. Most real decisions fall between those lines: a 10- to 15-year-old system with a moderate repair in the $500–$2,000 range. That is where the method below does its work.
What to have in hand
- The system’s age, from the install paperwork or the manufacture date on the nameplate.
- A written repair quote. With upfront pricing you see it before any work starts.
- A replacement estimate for comparable equipment. Ours are free.
- The repair history for the past two years.
- The refrigerant type, printed on the outdoor unit’s nameplate.
Factor 1: age
| Equipment | Typical lifespan |
|---|---|
| Central air conditioner | 15–20 years |
| Gas furnace | 15–25 years |
| Boiler | 20–30 years |
| Heat pump, mini-split | Judge by condition: they heat and cool, so they run in both seasons |
- Under 10 years: usually worth repairing; most parts have life left.
- 10–15 years: weigh the cost carefully; a major component failure leans toward replacement.
- Over 15 years: lean toward replacement for any major repair.
In San Jose the two halves of a system age differently. The AC works hard through hot summer afternoons, while the furnace has a light load through mild winters. A 20-year-old furnace can be in better shape than a 15-year-old air conditioner in the same house, so judge each piece on its own.
Factor 2: the 50% rule, and the age test that fixes it
The 50% rule: if the repair costs more than half of the replacement estimate, replace. It is quick, but it treats a 4-year-old system and a 16-year-old one the same.
The age × repair cost test: multiply the age in years by the repair quote. If the result is larger than the replacement estimate, replace. You can run it without dollar figures. Divide the repair quote by the replacement estimate to get a share, then multiply by the age:
- score above 1: replacement usually makes more sense;
- score below 1: repair usually does.
A repair that costs one-tenth of a new system scores 0.6 on a 6-year-old unit (repair) and 1.2 on a 12-year-old one (replace). The older the system, the smaller the repair it takes to tip the answer.
Factor 3: repair history
Keep a running total of service calls, parts and labor. The warning signs are three or more repairs in two years, the same part failing again, bills that grow every year, and a system that goes down several times a season.
Parts age together. On an old system a failed compressor often comes with worn capacitors and contactors, and a cracked heat exchanger means the rest of the furnace has seen the same years of heat. One major failure is often the first of several.
Factor 4: efficiency and refrigerant
Minimum efficiency standards for new equipment have been raised more than once since the mid-2000s, and since 2023 air conditioners and heat pumps are rated on the newer SEER2 test. An older system uses more power for the same cooling, and because a San Jose AC runs through long, hot afternoons, the gap shows on the bill. To weigh it, divide the efficient option’s extra cost by its estimated yearly saving. That is the payback in years; compare it with how long you plan to stay.
Refrigerant can decide the case on its own:
- R-22 has not been produced or imported in the US since 2020. Service relies on recovered and recycled stock, so a leak or a compressor failure on an R-22 system is a strong reason to replace.
- R-410A systems are still serviced normally.
Do not count on a federal tax credit: the one for efficient HVAC equipment ended for equipment installed after December 31, 2025.
Factor 5: comfort and design
Some problems no repair fixes: a system that never kept the house comfortable, rooms that are always too hot or too cold, humidity that stays high, noise you have stopped tolerating. If the system was sized wrong, installed poorly or fed by inadequate ducts, repairs only keep a flawed setup running. A replacement starts with a load calculation and a duct check, so the new system fits the house. In Evergreen, many tract homes have builder-grade equipment reaching replacement age, and correct sizing is the first thing to get right.
The method, step by step
- Safety first. A cracked heat exchanger, scorched wiring or a gas smell is not a cost question. Leave the equipment off until it is fixed; if you smell gas, leave the house and call from outside.
- Check the warranty on a young system: a covered part changes the share.
- Run the 50% rule. Above half the replacement estimate, replace.
- Run the age test. Age × (repair ÷ replacement): above 1 leans replace, below 1 leans repair.
- Apply the tie-breakers. R-22, three or more repairs in two years or a comfort problem push toward replacement. A first major repair on a system serviced every year pushes toward repair.
- Size up the repair. A minor repair under $500 on a system that runs well usually passes both tests. A moderate repair of $500–$2,000 is case by case, and steps 4 and 5 decide it. Above $2,000 on a system over 10 years old, replacement usually wins.
Worked examples
Share = repair quote ÷ replacement estimate. Score = age × share.
| System and repair | Age | Share | 50% rule | Score | Tie-breaker | Verdict |
|---|---|---|---|---|---|---|
| AC, capacitor and contactor | 7 | 0.05 | Repair | 0.35 | Serviced yearly | Repair |
| Heat pump, outdoor fan motor | 9 | 0.08 | Repair | 0.72 | First repair | Repair |
| AC, second refrigerant leak in two years | 11 | 0.08 | Repair | 0.88 | Repeat failure | Replace |
| Furnace, cracked heat exchanger | 12 | 0.20 | Repair | 2.4 | Repairs last year, safety | Replace |
| AC, compressor | 18 | 0.35 | Repair | 6.3 | R-22 | Replace |
| AC, compressor out of warranty | 5 | 0.55 | Replace | 2.75 | None | Replace |
Only the last example fails the 50% rule. Used alone, the rule would have said “repair” for three systems that end in replacement. The age test catches two of them, and the repair history catches the third.
Local notes
In Blossom Valley, many homes still run original equipment that is now around 40 years old. At that age almost any major repair fails the age test, so get a replacement estimate before paying for one. If you are replacing an old furnace and AC together, a heat pump covers both with one outdoor unit and suits San Jose’s mild winters; an older home may need an electrical capacity check first.
How we handle it
The technician diagnoses the fault and gives you the repair price, plus a replacement option when age or condition calls for it, with the reasons. You decide, without pressure. Start with AC repair, furnace repair or heat pump repair, or see the AC repair cost guide.