HVAC repair or replace calculator
Enter your repair quote, a replacement quote and what you spend on heating or cooling. You see what the common rules of thumb say and what each choice costs you per year, with the math shown.
Example values are filled in. Replace them with your own.
The three rules of thumb
- $5,000 rule. Multiply the unit's age by the repair quote. More than $5,000 points to replacing. From ACHR News (2014), where it was called a "starting point for discussion"; Trane also uses it. Blind spot: it ignores efficiency and the replacement price, so on a 12-year-old unit it flags any repair over $417.
- 50% rule. Divide the repair quote by the replacement quote. 50% or more points to replacing (Trane: "close to half the price of a new system"; ACHR News: repair if it is "less than half the cost"). Blind spot: it ignores the unit's age.
- 3/4-life plus 1/3-cost rule. Replace when the unit is past three quarters of its typical life and the repair costs more than a third of the replacement (ACHR News, 2014). Typical lives from DOE FEMP: central AC 24 years (North), 18 (Southeast), 25 (Southwest); heat pump 15; gas furnace 21.
How we calculate it
- Energy savings. Ratings are put on one basis first (SEER × 0.95 = SEER2 and HSPF × 0.85 = HSPF2 for split systems, RESNET 71i). Yearly savings = yearly cost × (1 − old rating ÷ new rating). For a furnace, use AFUE: going from 80% to 95% saves $15.79 per $100 of gas.
- Simple payback. (Replacement quote − repair quote) ÷ (yearly energy savings + other yearly repairs).
- Cost per year. Repair: the repair quote spread over the years it should buy, plus the extra energy the old unit uses, plus other repairs. Replace: the replacement quote spread over the new system's life. With a discount rate, the spreading uses the capital recovery factor i ÷ (1 − (1 + i)−n). If the two differ by less than 15% of the replacement's yearly cost, the result is a close call. That 15% band is our design choice, not a sourced figure.
- Difference and totals. Over the years the repair buys, repairing costs (repair per year − replace per year) × those years. The totals table runs both paths over the new system's life. The repair path buys the new system later, so the years of its life left at the end are subtracted at a straight-line value. The two methods give the same difference.
About R-22 systems
Your system uses R-22. It has not been produced or imported in the US since 2020, so service relies on recycled, reclaimed or stockpiled R-22. EPA does not require you to replace a working R-22 system. If the repair is a refrigerant top-up, ask whether the leak will be fixed, because a top-up alone may only last a season. (EPA, updated 2026-08-05)
Questions
What is the $5,000 rule for HVAC, and is it real?
Multiply the unit's age by the repair cost. If the result is more than $5,000, consider replacing. It is a rule of thumb that appeared in HVAC trade press in 2014 (ACHR News), not a standard. Some contractors say no such industry standard exists. It ignores efficiency and the replacement price: on a 12-year-old unit it flags any repair over $417, even a capacitor. Use it as a prompt to compare, not as an answer.
My AC is 20 years old but works fine. Should I replace it?
Age alone is not a reason. ENERGY STAR's 10-year (AC/heat pump) and 15-year (furnace) marks mean "start planning". Get replacement quotes before an emergency, so you're not choosing in a heat wave.
Is it worth paying to recharge an R-22 system?
Production and import ended in 2020, and service uses recycled or stockpiled R-22 (EPA). EPA does not require replacement. A recharge without a leak repair may last a season. Enter R = 0.5 or 1 and see what that repair costs per year.
The technician says the coil is leaking and wants to replace the whole system. What should I enter?
The coil replacement is a repair quote, so get it priced. Enter both quotes, and get a second opinion on a major repair to an older unit.
Can I include the federal tax credit?
No. The 25C credit does not apply to equipment placed in service after 2025-12-31 (IRS). Subtract any utility rebate you've been approved for from the replacement quote.
My quote replaces both the furnace and the AC. What do I enter?
If your quote replaces both the furnace and the AC, run the calculator for the unit that needs the repair, and ask the contractor for a price on replacing that unit alone.