Read the age before you compare prices
The manufacture date is on the nameplate, usually on a side panel. Age is what the $5,000 rule and the age rule both multiply against. A roof uses the install year instead of a nameplate.
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Repair or replaceRepair or replace calculator
Enter the age, the repair quote and the price of a new one. The calculator runs the $5,000 rule, the 50% rule and an age check, then compares the cost per year of repairing now with replacing now.
Reviewed 8 October 2026
Written and maintained byMantu Kumar
Evidence review8 October 2026
Calculation rulesRead the methodology
Quality standardEditorial policy
Key facts at a glance
- $5,000 rule: age × repair cost above $5,000 points to replacing heating or cooling.
- 50% rule: a repair at half the price of new is rarely worth it.
- Central AC lasts about 12–15 years; a gas furnace 15–20.
- A tank water heater lasts about 8–12 years; tankless about 20.
- An asphalt shingle roof lasts about 20–30 years.
- Homeowners insurance does not pay for wear or mechanical breakdown.
Sources: CBS News, InterNACHI and the Department of Energy, listed at the end of this page.
Repair now or replace now
No email · nothing sentLook before you decide
Read the age, the condition and the warning signs
The same three questions apply to an air conditioner, a furnace, a water heater or a roof: how old it is, what the repair costs, and what a new one costs.
The three detail views below enlarge parts of the same photograph. Use them with the checks underneath.
Get both numbers in writing
The calculator compares the repair you were quoted with the price of a new unit. A blank page is intentional. Do not decide from a verbal price.
Look for the failure you cannot patch
Rust through the cabinet or a compressor that has failed is usually a replacement, not a repair. The same test covers a furnace, heat pump, water heater and roof. Pick the one you actually have.
Before you pay for the repair, confirm these
- Age
- Manufacture date from the label or the install invoice
- Diagnosis
- What failed, what is likely to fail next and whether parts are still made
- Replacement quote
- A written price for a new unit to compare against the repair
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On this page
The $5,000 rule for heating and cooling
HVAC technicians often use a quick test: multiply the age of the system by the repair cost. Above $5,000, replacing is usually the better long-term choice. A 12-year-old air conditioner with a $900 repair scores $10,800, so it fails the test; a 5-year-old one with the same repair scores $4,500 and is worth fixing.
The 50% rule
If a repair costs half the price of a new unit or more, replacing usually gives better value, especially late in the item’s life. The rule works for appliances, water heaters and roofs as well as heating and cooling.
How long home systems last
| System or item | Typical life | Typical replacement |
|---|---|---|
| Central air conditioner | 12 to 15 years | $5,000 to $11,000 with a furnace |
| Gas furnace | 15 to 20 years | $3,500 to $7,500 |
| Heat pump | 12 to 15 years | $6,000 to $14,000 |
| Tank water heater | 8 to 12 years | $1,300 to $3,000 |
| Tankless water heater | 18 to 20 years | $3,000 to $7,500 |
| Asphalt shingle roof | 20 to 30 years | $6,800 to $32,000 |
Cost per year is the fairer comparison
A $900 repair looks cheap next to a $7,500 replacement, but the repair may only buy two or three more years. The calculator divides the repair by the extra years it is likely to buy, adds the energy you keep paying for with an older unit and any further repairs, and compares that with the new price spread over a full expected life.
When repairing still makes sense
- The system is in the first half of its life and the repair is a single part, such as a capacitor, igniter or thermocouple.
- You plan to sell soon and buyers will not pay for a newer unit.
- It is the middle of a heat wave or cold snap and a quick repair buys time to collect replacement quotes.
- A covered warranty pays for the part and you only pay labor.
Replace sooner if the system uses R-22 refrigerant, is a safety risk such as a cracked heat exchanger, or a leaking tank. Leaks and failures can also cause water damage; see the water damage calculator.
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Questions
What is the $5,000 rule for HVAC?
Multiply the age of the heating or cooling system in years by the repair cost. If the result is more than $5,000, replacing is usually the better long-term choice; below $5,000, repairing usually makes sense.
What is the 50% rule for repair or replace?
If a repair costs 50% or more of the price of a new unit, replacing usually gives better value, especially for an item in the last part of its expected life.
How long does a central air conditioner last?
Typically 12 to 15 years, and longer in mild climates with regular maintenance. Gas furnaces often last 15 to 20 years.
Should I repair a 10-year-old water heater?
A tank water heater usually lasts 8 to 12 years. Small part repairs such as a thermostat or element can be worth it, but a leaking or rusting tank should be replaced.
Is it worth repairing a 20-year-old roof?
A small repair can buy time, but an asphalt roof near the end of a 20 to 30 year life usually needs replacing within a few years. Compare the repair with the roof’s cost per year of remaining life.
Does a new HVAC system save money on energy?
Often. A newer, higher-efficiency system can cut cooling and heating costs, commonly by a few hundred dollars a year, depending on the old unit, the climate and your use. Enter your own estimate in the calculator.
Will insurance pay to replace a worn-out system?
No. Homeowners insurance does not pay for wear, age or mechanical breakdown. An equipment breakdown endorsement or home warranty may cover some failures.
Related
- HVAC replacement cost calculator — price a new system
- AC size calculator — check the right tonnage first
- Water heater cost calculator — tank and tankless prices
- Roof replacement calculator — price a new roof
How to use this result
These are common rules of thumb and a simple cost-per-year comparison, not a diagnosis. A licensed technician’s inspection, safety issues and the availability of parts can override the result.
Evidence trail
Reviewed 8 October 2026Sources used to check this tool
Rules of thumb come from trade and consumer guidance; life expectancies from inspection industry data and the Department of Energy.
$5,000 ruleCBS News: the $5,000 rule for HVAC
Life expectancyInterNACHI home system life expectancy
EfficiencyEnergy Saver: central air conditioning
Water heatersEnergy Saver: water heating
These organizations do not endorse ReplaceCost. The written policy, program rules, contractor scope and applicable law control the real result. See the full methodology for the source hierarchy and update process.
Repair or replace
Put the repair quote next to the price of new
Age, repair cost and cost per year give a clearer answer than the repair bill alone.
$5,000 rule
Age times repair cost above $5,000 points to replacing.
50% rule
A repair at half the price of new is rarely worth it late in life.
Expected life
Most systems give warning signs in their last quarter.
Energy savings
A newer unit can pay part of its cost back each year.
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