The HVAC tech is standing in your mechanical room. The compressor is out. He can fix it for $1,850 or replace the whole condenser for $4,400.
The unit is twelve years old.
You have about ninety seconds to decide, because the tenant has been without AC for two days and it’s August.
This is the wrong moment to be doing math you haven’t done before. The repair-or-replace decision needs a framework you already trust, before you’re standing in the mechanical room.
The 50% rule and where it actually applies
The most widely-cited heuristic is the 50% rule: if the cost of repair exceeds 50% of the cost of replacement, replace.
It’s a decent starting point. It’s also incomplete.
The 50% rule works cleanly when the alternative is a like-for-like replacement and the system isn’t near end-of-life. It breaks down when:
- The unit is already past 75% of its expected life.
- Parts availability is limited (the next failure will be worse).
- A higher-efficiency replacement materially cuts operating costs.
- An insurance claim is in play and “deferred maintenance” is a denial reason.
The honest version of the rule is: 50% is the upper bound, not the threshold. If you’re over 50%, replace, full stop. If you’re between 25% and 50%, age and parts availability decide. Under 25%, repair almost always wins unless other factors push you over.
Age thresholds you can actually use
Every system has an expected useful life. Manufacturer claims are optimistic. The numbers below are what landlords and property managers see in practice:
| System | Expected life | The threshold that tips toward replace |
|---|---|---|
| Central air conditioning | 12–15 yrs (10 coastal, 18 dry inland) | Past 15, almost any major repair argues for replacement |
| Furnaces (gas) | 15–20 yrs | Cracked heat exchanger is replace at any age — safety issue |
| Furnaces (electric resistance) | 20–25 yrs | Past 18, lean replace on major repair |
| Heat pumps | 12–15 yrs | Past 12, compressor work rarely pencils |
| Water heaters (tank) | 8–12 yrs | A leaking tank is always replace |
| Water heaters (tankless) | 15–20 yrs | Heat exchanger failure is replace |
| Refrigerators | 13–17 yrs | Compressor work past 10 years rarely pencils |
| Dishwashers | 8–12 yrs | Past 8, replace on any repair over $300 |
| Washing machines (top-load) | 10–13 yrs | Past 10, replace on motor or transmission |
| Washing machines (front-load) | 8–11 yrs | Bearing failure is the typical replace moment |
| Dryers | 10–15 yrs | Past 12, replace on any repair over $250 |
| Ovens & ranges | 13–18 yrs (gas > electric) | Control-board failure usually argues replace |
| Garbage disposals | 8–12 yrs | Almost always replace — units are cheap, labor is the same |
| Toilets (porcelain) | 25–50 yrs | Cracked tank or bowl is replace; internals are a 5–10 yr swap |
| Water supply: copper | 50+ yrs | Pinhole leaks at 40+ argue for re-pipe |
| Water supply: PEX | 40–50 yrs | Replace at signs of UV / chemical degradation |
| Water supply: galvanized | 40–60 yrs | Most are at end of life — plan a re-pipe |
| Water supply: polybutylene | Any age | Replace on sight — known liability |
| Sewer: cast iron | 50–100 yrs | Recurring backups argue for lining or replacement |
| Sewer: clay | 50–60 yrs | Root intrusion at 30+ argues for replacement |
| Sewer: PVC | 100+ yrs | Replace only on physical damage |
For HVAC and water heaters especially, write the install date on the unit with a marker the day you take ownership. You’ll thank yourself a decade later.
The hidden cost of repair on aging systems
The 50% rule misses what comes next. A repaired 14-year-old AC isn’t a fixed AC, it’s an AC that just told you what’s wearing out, with the rest of the components on the same wear cycle.
Run the math over the expected next three years, not just today’s repair:
- Today: $1,850 repair.
- Year 1 likely failure: capacitor, $300.
- Year 2 likely failure: contactor or fan motor, $600.
- Year 3 likely failure: coil leak or compressor, $1,400.
Total over three years: $4,150, already past the $4,400 replacement, with no remaining life at the end.
This isn’t pessimism. It’s pattern recognition. Components that share an operating environment fail in clusters. Once one major part on an aging system goes, the rest are not far behind.
A 5-year-old system fails differently. Component failures there tend to be isolated, a single bad part, the rest of the system fine. Repair is usually right.
Energy efficiency and the operating-cost line
A new SEER-19 air conditioner uses roughly 35-40% less energy than a SEER-10 unit from 2008. For a tenant-paid utility, you might think this doesn’t matter to you. It does, efficient utilities reduce tenant turnover, support higher rent, and increasingly show up in jurisdictions that require energy disclosures at lease signing.
For an owner-paid utility (common in older multifamily, master-metered properties), the math is even sharper. A 2,000-square-foot unit running a 14-year-old AC versus a new one might cost $400 to $700 more per cooling season. Over a five-year remaining life on the old unit, that’s $2,000 to $3,500, enough to flip a marginal repair-or-replace call.
Heat pumps in particular have moved fast. A 2025-model cold-climate heat pump replacing a 2012 furnace plus AC pair often pays for itself in 6 to 9 years on operating costs alone, plus rebates that didn’t exist five years ago.
Don’t replace solely on efficiency math. But include it.
Insurance and code: the third variable
When a system fails badly (flood, fire, leak that damages other units) your insurance carrier asks two questions. How old was the system? When was the last documented maintenance?
A 16-year-old water heater that fails and floods two units isn’t a covered loss in the same way a 4-year-old one is. The carrier may pay the water-damage claim but exclude the water heater itself as deferred maintenance, or reduce coverage citing age.
A 13-year-old furnace with a cracked heat exchanger that you “repaired” instead of replaced becomes a liability exposure. If a CO incident occurs and the vendor’s notes flag “near end of life,” you’re in a bad spot.
Code changes also force replacement. Refrigerant changes (R-22 phaseout to R-410A, now R-454B) mean some repairs are no longer possible, parts simply aren’t manufactured. Lead-solder plumbing repairs in pre-1986 systems can trigger lead-line abatement requirements. Knob-and-tube electrical work often requires full circuit replacement if you touch it.
When in doubt, ask the vendor: “Is this a code-compliant repair, or does it bring the whole system into a gray area?”
The decision tree
Put it together and the decision flow looks like this:
- Is the unit past 75% of its expected life? If yes, lean replace on any repair over 25% of replacement cost.
- Is the repair cost over 50% of replacement? If yes, replace.
- Are parts still available and supported? If no, replace, the next failure has no fix.
- Is this a safety or code issue? (Cracked heat exchanger, gas leak, electrical hazard, lead/asbestos exposure.) If yes, replace.
- Would an efficient replacement save more in operating costs over remaining ownership than the cost gap? If yes, lean replace.
- Is there an active insurance claim or recent claim history? If yes, replace, protect the next claim.
- None of the above? Repair.
The tree resolves about 80% of repair-or-replace decisions cleanly. The remaining 20% are judgment calls. The point of the tree isn’t to remove judgment. It’s to make sure you’ve thought about each variable instead of reacting to the vendor’s quote.
Run the numbers
Punch the quote, the unit, and the age into the calculator. It combines the 50% rule with remaining useful life and gives you the recommendation in one line — useful when you need to justify the call to the owner.
The repair-or-replace decision is a tax decision
Repairs are deductible in the year of expense. Replacements get capitalized and depreciated over 27.5 years (residential rental property).
The same $4,400 spent on an AC condenser is, depending on how it’s classified:
- Repair (deduct now): roughly $4,400 of deduction this year.
- Replacement / improvement (capitalize): roughly $160 of depreciation per year for almost three decades.
The difference, at a 24% marginal rate, is roughly $1,020 of cash flow this year that you either get or don’t get.
The IRS’s Tangible Property Regulations (the “BAR” tests, Betterment, Adaptation, Restoration) decide which bucket. Critically, “restoration of a major component or substantial structural part” is capitalized. A new compressor is arguably a component; a new condenser is a major component; a new full HVAC system is unambiguously a capital improvement.
This is why receipt language matters. If the work is genuinely a repair, the invoice should say so. If it’s a replacement, capitalize it correctly, trying to expense a clear capital improvement triggers exactly the kind of audit nobody wants.
For more on the receipt side, see maintenance receipts: what to save and for how long.
Edge cases worth naming
A few situations don’t fit the tree neatly:
Mid-tenancy failures with a long-term tenant. Sometimes replacement is the right call purely because the disruption and tenant goodwill matter more than the math. A reliable five-year tenant getting a new system mid-lease is cheap insurance against turnover.
Inherited systems on new acquisitions. Always assume the previous owner deferred maintenance. Budget for at least one major replacement in years one to three. A unit that survives the inspection often fails within 18 months.
Multiple aging systems at once. When the AC, water heater, and one appliance are all near end of life, bundle the replacements. Vendor mobilization costs are real; doing them on three separate calls costs more than one coordinated week of work.
Vacant unit replacements. Always cheaper than occupied-unit replacements. If a system is borderline and the unit is about to turn, replace during the turn. You’ll never get a better window.
Document the decision either way
Whether you repair or replace, document the decision and the reasoning. A short note attached to the work order:
- What failed.
- What the vendor recommended (repair vs replace, with quoted costs for each).
- What you chose.
- Why, citing age, cost ratio, parts, safety, or insurance posture.
This note is worth nothing in normal operations and worth a great deal in two scenarios: an insurance claim where the carrier questions the maintenance history, and a tax audit where the classification is contested.
A Maintenance Record PDF captures all of this in one place (the work, the photos, the receipt, and the decision context) for $5 per record.
The closing thought
The right answer to repair-or-replace isn’t always the cheapest answer today. It’s the cheapest answer over the remaining ownership period, adjusted for the failure risk you’re underwriting and the records you’ll need if it goes wrong.
Get the tree on paper. Make the call with confidence. And document maintenance with photos and a record every time, so the next decision (and the next dispute) starts with evidence instead of memory.
