Understanding your result
The headline is the saving per year in dollars, with the kilowatt-hours saved, the percentage reduction in the cooling bill and, if you entered an extra cost, the simple payback in years. The two bars show the annual cost of the old and the new system side by side; the gap between them is the headline. The stats give the two annual costs and the total saving over the number of years you chose, which is the figure to weigh against the extra price.
The table shows the old rating converted to SEER2 so the two are compared on the same scale, the cooling delivered per year in million BTU (the same for both systems, since the house’s need does not change), and the electricity each system uses to deliver it. If the payback is longer than the years you are totalling over, the note says so; it does not mean the better unit is a bad buy, only that the bill alone does not justify it and the quieter, steadier running of a high-efficiency variable-speed unit has to be worth the difference to you.
For the cost of running either system month by month, use the AC running cost calculator. For the same comparison on a furnace or heat pump, with AFUE or HSPF2 instead of SEER2, use the HVAC upgrade payback calculator, and for what the replacement itself costs, the HVAC replacement cost calculator.
How we calculate this
SEER2 is BTU of cooling per watt-hour of electricity over the test season, so the electricity for a year’s cooling is the cooling in BTU divided by SEER2 and by 1,000 to get kilowatt-hours. The 0.95 conversion from SEER to SEER2 comes from the DOE’s 2023 test procedure change and is tabulated with the other ratings on the efficiency ratings table.
Equivalent full-load hours describe how much cooling the climate demands; they are the season’s cooling divided by the system’s capacity, and they let the comparison be made without knowing hour-by-hour run times. The default of 1,200 is a mid-US figure; the guide to heating and cooling degree days explains how to estimate yours. The payback is simple payback, without interest or electricity price rises, both of which would shorten it.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| SEER to SEER2 | × 0.95 | US DOE 2023 test procedure (Appendix M1); about 4.5 to 5% lower for the same equipment |
| Full-load cooling hours | 1,200 a year | Mid-US figure; ranges from about 500 (north) to 2,800 (Gulf Coast); DOE and utility equivalent-full-load-hour tables |
| Electricity price | $0.17 per kWh | US residential average, EIA Electric Power Monthly, 2025 |
| New SEER2 | 15.2 | A common step above the 2023 minimums of 13.4 (north) and 14.3 (south) |
| Extra cost | $2,000 | Typical premium for one efficiency tier on a 3-ton system, 2024 to 2025 cost surveys; enter the difference between your quotes |
| Years totalled | 15 | Typical service life of a central air conditioner (DOE, ASHRAE service-life data: 15 to 20 years) |
Assumptions last reviewed October 7, 2026.
The calculator does not include rebates or tax credits, which can cut the extra cost substantially and vary by state and year; enter the extra cost net of any you qualify for. It does not count the fan’s electricity, the better dehumidification of variable-speed units, or the chance that the old unit’s real efficiency has fallen below its label through age, a dirty coil or low refrigerant charge, which would make the saving larger than shown. The guide to SEER2, HSPF2, AFUE and COP explains what each rating measures.
Two worked examples
Replacing a 20-year-old unit with the common mid tier
Old SEER 10, new SEER2 15.2, 3 tons, 1,200 full-load hours, $0.17 per kWh, $2,000 extra over the minimum-efficiency unit, 15 years.
- Old rating on today’s scale: 10 × 0.95 = SEER2 9.5
- Cooling per year: 3 × 12,000 × 1,200 = 43.2 million BTU
- Electricity: old 43,200,000 ÷ 9,500 = 4,547 kWh; new 43,200,000 ÷ 15,200 = 2,842 kWh
- Saving: 1,705 kWh × $0.17 = $289.89 a year (38%)
- Payback: $2,000 ÷ $289.89 = 6.9 years; saving over 15 years $4,348
A payback under seven years on a unit that lasts fifteen is a sound return. Note that most of the saving comes from replacing the old unit at all: a minimum-efficiency 13.4 SEER2 unit would already save about $225 a year, and the $2,000 step to 15.2 buys the remaining $65 a year.
A hot climate, cheap power, a big step up
Old SEER 13, new SEER2 18, 4 tons, 2,200 full-load hours, $0.14 per kWh, $3,500 extra, 15 years.
- Old rating: 13 × 0.95 = SEER2 12.4
- Cooling per year: 4 × 12,000 × 2,200 = 105.6 million BTU
- Electricity: old 8,551 kWh; new 5,867 kWh
- Saving: 2,684 kWh × $0.14 = $375.75 a year (31%)
- Payback: $3,500 ÷ $375.75 = 9.3 years; saving over 15 years $5,636
Even with 2,200 hours the payback is over nine years, because electricity is cheap and the old unit is not that bad. The 18 SEER2 unit is a variable-speed system, and in a hot, humid climate its steadier running and lower indoor humidity may be the real reason to buy it; the bill alone makes a weaker case than in the first example.
Where to find your inputs
Current rating. On the yellow EnergyGuide label if it is still on the unit, on the AHRI certificate from the installation, or by searching the model number in the AHRI directory. Choose SEER or SEER2 according to which the label shows; anything installed before 2023 is SEER.
New SEER2. On the quote and on the AHRI certificate for the matched indoor and outdoor units. The rating belongs to the pair, not the outdoor unit alone.
Full-load hours. From a smart thermostat’s run-time history (total compressor hours in a year), or from your climate as described in the FAQ. If in doubt, run the calculator with two figures.
Extra cost. The difference between two quotes for the same job at different efficiency tiers, after any rebate or tax credit.
Common mistakes
- Comparing SEER with SEER2. An old SEER 16 is not better than a new SEER2 15.2; it is the same efficiency.
- Using national average hours in Phoenix or Seattle. Full-load hours vary fivefold across the country and the saving varies with them.
- Crediting the whole saving to the efficiency tier. Most of the saving against an old unit comes from any new unit; the tier premium buys only the difference between two new ratings.
- Forgetting the ducts. Leaky ducts waste the same share of cooling whatever the SEER2; seal them first, or at the same time.
- Ignoring size. A new unit a size too big short-cycles and never reaches its rated efficiency.
- Treating payback as the whole decision. Quietness, humidity control and comfort on hot nights are real, if unpriced, and a variable-speed unit delivers them.
Questions people ask
- How much does upgrading from SEER 10 to SEER2 15.2 save?
- About a third of the cooling electricity, because a SEER 10 unit is about SEER2 9.5 on today's scale and 9.5 ÷ 15.2 = 0.625. For a 3-ton system running 1,200 full-load hours a year at 17 cents per kWh, the old unit uses about 4,550 kWh ($773) and the new one about 2,840 kWh ($483), a saving of about $290 a year. In a hot climate with 2,200 hours the saving is about $530 a year.
- What is the difference between SEER and SEER2?
- The same quantity measured under a different test. In 2023 the Department of Energy changed the test procedure to use a higher external static pressure that better reflects real ductwork, and the resulting SEER2 numbers are about 4.5 to 5% lower than SEER for the same equipment. A SEER 16 unit is about SEER2 15.2; a SEER 14 unit about SEER2 13.4, which is why the new northern minimum is 13.4. Always compare like with like.
- Is a higher SEER2 worth the extra cost?
- It depends on your cooling hours and your electricity price. Going from the minimum (13.4 or 14.3) to 16 or 17 SEER2 typically costs $1,000 to $2,500 more and saves 10 to 20% of the cooling bill; in a hot climate with 2,000 or more cooling hours at 15 cents or more per kWh that pays back in 5 to 8 years, while in a cool climate with 600 hours it may never pay back on the bill alone. Variable-speed units at 18+ SEER2 also bring quieter running and better humidity control, which the payback does not count.
- What are equivalent full-load cooling hours?
- The number of hours a year the system would have to run at full capacity to deliver the season's cooling. It is a way of describing a climate, about 500 hours in Minneapolis or Seattle, 900 in Chicago, 1,200 in St. Louis or Washington DC, 1,600 in Atlanta, 2,200 in Dallas, 2,500 to 2,800 in Houston, Phoenix and Miami. A smart thermostat's run-time history gives your own figure; the degree-days guide explains how to estimate it from your climate.
- Does the saving depend on the size of the system?
- In proportion. The saving per year is the cooling delivered multiplied by the difference between 1 ÷ old SEER2 and 1 ÷ new SEER2, and the cooling delivered is tons × 12,000 × hours. A 4-ton system saves a third more than a 3-ton one for the same ratings and hours. This is also why right-sizing matters, since an oversized new unit delivers the same cooling at lower efficiency because it short-cycles.
- Why does the calculator say the saving depends on tight ducts?
- Because the rating is measured at the equipment, and ducts that leak 20 to 30% of the air into an attic or crawl space lose that share of the cooling before it reaches the rooms. A SEER2 18 system on leaky ducts delivers less cooling per kWh than a SEER2 14 system on sealed ones. Sealing ducts typically costs a few hundred to $1,500 and often saves more than the step from 16 to 18 SEER2; the duct leakage calculator estimates the loss.