Central AC Replacement Calculator

This calculator weighs keeping your central air conditioner against replacing it with a new one. Describe the old unit by the year it was made or by the SEER on its nameplate, enter the new unit's SEER2 from its AHRI certificate or compare at the federal minimum, and give your system size and state, or your old unit's yearly electricity from your bills. It works out your cooling need, each unit's yearly electricity and cost, the yearly saving, the net cost of the new system, the simple and discounted payback, and the cost over the years you choose of keeping the old unit, replacing it now, or replacing it when it wears out.

Ratings and climate figures come from federal sources only: DOE efficiency standards and test procedures, NOAA climate normals and EIA electricity prices. Older and newer ratings are never mixed. You set the installed price; the opening example and each worked example carry a round illustrative price, labelled as such.

Purpose and model boundary

This calculator compares keeping the central air conditioner you have with replacing it with a new one. It works out the cooling your home needs, from your bills or from your state's climate and your system's size, the electricity each air conditioner needs to deliver it, and the cost at your electricity price, and sets the yearly saving against what the new system costs installed. Over the number of years you choose, it compares keeping the old system, replacing it now and, when you say how many years the old one has left, replacing it when it wears out.

Every figure on this page is computed by the spreadsheet; the page adds nothing to it. It covers cooling running cost and purchase cost only, for the same ducts; a change of distribution system is not modelled.

Inputs and units

• The old air conditioner: split system or single package, described by the year it was made, for which the calculator uses the federal minimum SEER for your state's region, or by its SEER from the nameplate or AHRI certificate (6 to 40) with the basis of that rating: SEER2 (rated 2023 or later), SEER (rated before 2023), or Unknown.
• Your cooling need: the size of your system, 0.5 to 6 tons, and where the need comes from: an estimate from your state and system size, or your old air conditioner's yearly electricity from your bills. Optionally, your own cooling degree days, which replace your state's figure.
• The new air conditioner: split system or single package, with its SEER2 from the AHRI certificate (10 to 40), or compared at the federal minimum for your state.
• Price: the state, which sets the default electricity price, and your own electricity price in dollars per kWh (0.01 to 2.00), optional.
• Purchase and finance: the installed price of the new system, which is always yours to set; extra work such as permits, electrical or duct work; sales tax; verified incentives; removal; the old unit's sale value; yearly upkeep of each unit; the years the old unit has left; the new unit's expected life; the yearly change in electricity prices; the discount rate; and the years to compare.

Heating and cooling needs are in million Btu (MMBtu) a year of heat delivered or removed. Electricity is in kWh, fuel in US gallons or therms, efficiency ratings in Btu per watt-hour (CEER, SEER2, HSPF2) or as a fraction (AFUE), and money in dollars.

Governing relationships

• Estimated need: cooling need = system size (tons x 12,000 Btu/h) x 1,000 cooling hours x your state's cooling degree days / the US figure. The 1,000 hours are DOE's representative cooling use cycle from the 2016 edition of its test-procedure rule; scaling them by your state's degree days is this calculator's own, labelled approximation.
• Need from your bills: your old air conditioner's yearly electricity is turned back into the heat it removed, using its own rating.
• Older and newer ratings are not mixed. A SEER rating from before 2023 is put on the SEER2 basis with the exact ratio of DOE's equivalent standard levels for its product class, from DOE's January 2017 direct final rule (82 FR 1786): 13.4/14 for a split or single-package air conditioner. That ratio translates standard levels, so applying it to one old unit is an approximation, and the rating note says so. With an Unknown basis the old rating is used as it stands, which makes the old unit look more efficient than it is, so the saving is understated.
• Electricity: cooling kWh = cooling need in Btu / (SEER2 x 1000).
• Yearly cost = electricity x electricity price + upkeep; the yearly saving is the old cost minus the new cost. Payback and present value follow the rules shared with the other replacement calculators, with nothing counted twice.

Calculation sequence

The spreadsheet first checks the inputs and finds each air conditioner's rating, the climate figures and the electricity price. It works out the cooling need once, shared by both units, reduces each unit to the electricity it uses per million Btu of cooling, and from those computes the yearly electricity, costs and saving; the purchase cost, the paybacks, the present values and the year-by-year cash flow follow. The sensitivity table uses the same per-MMBtu figures, so it cannot disagree with the main result. Consistency checks, including that your bills are reproduced from the computed need on the bills route and that the discounted cash flow reaches the same net present value as the closed-form formula, run before the status is returned.

Outputs and interpretation

The results show the yearly cooling need, the cooling degree days used, and for each air conditioner the rating used (after any conversion), the yearly electricity, and the yearly energy and total cost; then the yearly saving in dollars and kWh, the net cost of the new system, the simple and discounted payback, and the cost of each path. A note states where the need came from (your state's degree days and DOE use hours, or your bills) and another whether the old rating was converted.

The cash-flow table shows each year of the years compared: the cost of each path, the net benefit of replacing now, and its cumulative, discounted and cumulative discounted values. The sensitivity table shows the yearly saving with the cooling need scaled by 0.50, 0.75, 1.00, 1.25 and 1.50, at the same multiples of the electricity price used.

The first chart, “Cumulative net benefit of replacing now, by year”, shows Undiscounted and Discounted by year. The second chart, “Cost over the years compared”, shows Total and Present value by option. The third chart, “Running cost in year 1”, shows Cooling electricity and Upkeep by unit, stacked.

Validation and status logic

The workbook returns one status, chosen in this order: NOT VALID, then CHECK, then OK.

• NOT VALID names the first problem: an old-unit source or type that is not one of its options; no federal minimum on file for that type, region and year made, in which case use the nameplate rating; a manual SEER missing or outside 6 to 40, or a rating basis that is not one of its options; a system size missing or outside 0.5 to 6 tons; the same problems for the new unit: a federal-minimum choice with no minimum on file, or a manual SEER2 missing or outside 10 to 40; a source of the need that is not one of its options, or a bills figure missing or outside its limits; the estimate needs degree days and your state has no figure and you have not entered your own; no electricity price, or your own outside 0.01 to 2.00 dollars per kWh; a missing installed price, or one outside its limits; a money amount, the years compared, the price change, the discount rate or a life in years outside its limits. NOT VALID is a refusal, not a numeric answer: every figure reads zero and is withheld.
• CHECK accompanies a computed result that needs the stated review: the old rating is the federal minimum for the year made; the old unit may be more efficient, so the saving may be overstated; an old SEER rating with an Unknown basis, or with no conversion ratio for its class, is used as if it were SEER2, so the saving is probably understated; zero cooling electricity on the bills route; no yearly saving, so there is no payback; the old unit's remaining life is shorter than the years compared, so read the end-of-life comparison.
• OK otherwise.

Assumptions and limitations

• No federal model list and no ENERGY STAR level. The ENERGY STAR certified central air conditioner list held no models when the data were collected, and the current ENERGY STAR specification covers heat pumps only, so there is no ENERGY STAR level for a cooling-only air conditioner. The new unit is described by its SEER2 from the AHRI certificate, or compared at the federal minimum.
• Two labelled approximations. The figures behind them are DOE's, but how this calculator applies them is its own: DOE's standard-level ratio is applied to one old unit's SEER, and DOE's national cooling hours are scaled by your state's degree days. Your bills route avoids the second, and a rating on the SEER2 basis avoids the first.
• Not modelled: adjusting your bills for a mild or hot year, solar and internal heat gains beyond what the degree-day base implies, humidity removal beyond the SEER2 test, and duct changes.
• A federal minimum is a floor, not a measurement. An old unit described by the year it was made may be more efficient than the minimum, so the saving may be overstated. The minimum depends on your state's region; where the minimum changed during a year, the newer, higher minimum is used; and for systems of 45,000 Btu/h and more in the Southeast and Southwest the floor used is slightly higher than theirs. Each of these keeps the saving on the low side. Wear with age is not modelled.
• Alaska, Hawaii and DC. NOAA publishes no statewide degree-day normals for any of the three. DC uses Maryland's figures; Alaska and Hawaii each use one NOAA station normal, at the Anchorage and Honolulu airports, labelled as a single station. Your own degree days replace any state figure, and the bills route works everywhere.
• Prices. The installed price of the new system is always your input; the workbook holds no price table. The opening example and each worked example carry a round illustrative price so that they compute, with the note: "Illustrative price for this example, not a quote or a current price. Prices vary: check current prices online or enter your own. Get a contractor quote."
• The default electricity price is a state average. Your own price from your bill overrides it.

Data and vintage

• Federal minimum ratings by year made and region: DOE energy conservation standards (10 CFR 430.32), with earlier editions of the Code of Federal Regulations (1997 and 2012) for the years before the current standard.
• Rating ratio and use hours: DOE's January 2017 direct final rule (82 FR 1786) for the SEER level ratio, and the 2016 edition of 10 CFR 430.23 for the representative cooling hours.
• Climate: NOAA NCEI statewide cooling degree-day normals for 1991-2020 (nClimDiv); the US figure covers the 48 contiguous states. NOAA calls these long-term averages rather than official normals, and its notes state neither the base temperature nor the weighting.
• Default price: EIA final 2025 average residential electricity prices by state (Form EIA-861).

Worked examples and prices

Prices are not part of the reference data: the price of the new unit is an input you set. The opening example and the five worked examples each use an illustrative price for the new unit, so that the example computes, and each says so: “Illustrative price for this example, not a quote or a current price. Prices vary: check current prices online or enter your own.”

Restrictions and non-computing states

The calculator enforces its numeric and choice limits before it accepts a result. A listed model that is not in its list or does not match the type chosen, a rating or quantity outside its limits, a missing installed price, and a missing electricity or fuel price where no default exists are refused by the workbook.

Errors and warnings

A request rejected by the page's input limits is not a computed result. A transport or service failure, a timeout or a cancelled run cannot establish a fresh workbook answer, and the last result stays on the page marked as out of date. Check your equipment's nameplate or AHRI certificate and your own bills before relying on a result for a purchase, and get a contractor quote for the installed price.

Sources and further reading

The calculator reads federal minimum ratings, rating conversion factors, climate figures and default electricity prices from reference tables inside the workbook. This calculator has no model list. Every table comes from a US federal source. The sources below publish the data and the rules the model applies. They do not endorse this calculator.

• DOE energy conservation standards, 10 CFR 430.32 (eCFR) sets the SEER2 minimums for central air conditioners made from 2023, by region, and the SEER minimums before them; earlier editions give the older levels (retrieved 2026-10-28).
• DOE test procedures, 10 CFR 430 subpart B (eCFR) defines SEER2 under appendix M1, which replaced SEER under appendix M for ratings from 2023; 10 CFR 430.23, CFR 2016 edition (govinfo) gives the representative 1,000 cooling hours a year (retrieved 2026-10-28).
• DOE direct final rule, 82 FR 1786, January 6, 2017 (Federal Register), Tables V-29 and V-30, gives the 2023 standard levels under the older and the newer test, whose ratio converts an older SEER (retrieved 2026-10-28).
• ENERGY STAR data portal catalog (EPA) lists the EPA's certified-product datasets; it has no central air conditioner dataset, and the filtered central air conditioner view returned no models (retrieved 2026-10-28).
• ENERGY STAR air-source heat pumps: information for partners (EPA) links the current ENERGY STAR specification, whose criteria cover heat pumps only, with no level for a cooling-only air conditioner (retrieved 2026-10-28).
• NOAA NCEI, Climate Divisional Database (nClimDiv) publishes statewide cooling degree-day normals, used here for 1991-2020 (retrieved 2026-10-28).
• NOAA NCEI, U.S. Climate Normals 1991-2020, station files gives the Anchorage and Honolulu airport normals that stand in for Alaska and Hawaii (retrieved 2026-10-28).
• EIA, Detailed state data (Form EIA-861) gives the average residential electricity price by state, used here for 2025 (retrieved 2026-10-28).
• EIA, Residential Energy Consumption Survey 2020, state data gives typical air-conditioning electricity per household by state for 2020, a cross-check for your own figure; it is not a value in the calculator (retrieved 2026-10-28).

This is an educational estimate of running and purchase costs for the equipment and prices you enter, not a product recommendation or a quote. Ratings are measured under federal test procedures, not in your home.