AC Savings Calculatoracsavingscalculator.com

How the numbers are computed

This page is the whole recipe. The calculator has no black box: every figure it shows comes from public weather data, the physics described below, and the inputs you give it. Where we assume something, the page says so; where the honest answer is "an upgrade isn't worth it for you," the calculator says that too.

The weather layer

The engine runs on typical-year weather for 2,684 US stations, derived from TMYx typical-meteorological-year files (2009–2023 period) assembled from NOAA/NCEI Integrated Surface Database observations, with ERA5 reanalysis gap-fill. For each station we reduce the 8,760-hour year to a table of hours spent at each outdoor temperature (1°F bins), with the coincident outdoor moisture for each bin. We publish only these derived hour-count tables — meteorological facts computed from the public record — never the source files themselves.

Your zip code is matched to the nearest station by distance from the zip's Census-defined population centroid. We deliberately show the analysis for "near {your city}" rather than naming the station. If no station lies within 150 miles of a zip (a handful of remote areas), the calculator says so instead of quietly using far-away weather.

The cooling model

Cooling load is computed with the bin-hour method: for every temperature bin above the house's cooling balance point, the load is proportional to the temperature difference. How big that load is comes from the system you described, and here this calculator parts ways with most others. The usual assumption is that the installed equipment exactly meets the house on a design day. Installed systems do not work that way: measured runtime from 5,014 smart-thermostat homes (Kim et al. 2025) puts real installs at about 1.4 times the design-day load, and shows the design day itself running well above 95 °F across the desert Southwest and much of Texas. This calculator uses both facts, so the hours and dollars it prints are calibrated to measured runtime rather than to a nameplate. A calculator that skips this overstates every absolute dollar figure by roughly a third. The percentage saving between two systems does not depend on it, which is why other calculators can be right about the percentage and high on the dollars. Each bin's load is then divided by the equipment's efficiency at that condition — not the single sticker number. The model applies:

The heating model

Heating uses the same bin-hour framework below the heating balance point, calibrated from your furnace's sticker size and your area's design temperature. Fuel systems are priced by AFUE with a cycling adjustment for oversized single-stage equipment; a furnace's combustion efficiency is held at its sticker rating regardless of age — unlike compressors, heat exchangers don't meaningfully lose burn efficiency, so we don't manufacture phantom savings from an "old" furnace. Heat pumps are priced with temperature-dependent COP and capacity curves (an HSPF2 rating tells us the average; the curve tells us what January costs), including auxiliary resistance heat when the heat pump can't carry the load, and dual-fuel systems switch to the furnace below the economically-correct switchover temperature (bounded by what real dual-fuel controls allow). Where a heat-pump-versus-furnace comparison is on screen, we also show the crossover temperature — the outdoor temperature at which your prices make the two equally cheap to run — because that single number explains the verdict.

Why there is no per-house humidity number

The engine does model indoor moisture: a balance between the moisture that leaks in and is generated indoors and the moisture the coil removes while the compressor runs, which depends on compressor class and part load. That balance feeds the cooling load in every dollar figure above, and it is why a variable-capacity system is credited with more dehumidification per running hour than a single-stage one.

We do not print a per-house humidity figure from it. Checked against measured indoor humidity in 56 monitored Florida homes (Florida Solar Energy Center's Phased Deep Retrofit study, 2012–2016), the model's level could be brought within a few points of measurement, but the figure people would actually read, hours a year above a comfort line, turned out to be far more sensitive to unmeasurable house-by-house details (how much condensate re-evaporates off the coil between cycles, above all) than any dollar figure on the page. A number that can honestly move by a factor of five for the same house is not a number worth printing next to one that moves by fifteen percent. The comfort case for variable-capacity equipment, lower indoor humidity, lower noise and a steadier room temperature, rests on published measurements instead, cited where it appears.

Prices

Electricity, natural gas, and heating-oil prices default to state residential averages and are always editable — a real bill beats any average. Defaults are kept current from U.S. Energy Information Administration residential price series; each release is dated in the data files. The analysis is held at today's prices over the 5/10/15-year horizons — we don't forecast energy markets, and we say so rather than hiding an escalation assumption inside the math. The numbers also assume standard, unsubsidized rates: some utilities offer discounted heating rates (dual-fuel and off-peak programs) or equipment rebates that can materially change the answer — worth one call to your utility.

How this differs from the usual savings calculator

Most SEER savings calculators on the web run the same short formula: nameplate tons, times 12,000 BTU, times a fixed count of "cooling hours" for your city, divided by the old SEER and again by the new SEER, times a flat state electricity rate. It is a fine napkin. It also has no house in it, no age on the old unit, and no way to tell you what your own habits change. Four things this tool does that that formula cannot, in the order they move the answer:

The consequence: the number you saw somewhere else was computed for no house in particular. At the default settings this calculator will usually land below it, because of the sizing and age items; a household that keeps the house at 72 will land near it or above it, and a household at 78 well below. That spread is not noise, it is the part of the answer that is actually yours, and it is the reason the tool asks. Every constant is on this page.

What we deliberately leave out

Sources & credits

The honest fine print

Everything here is an estimate for planning, not a quote or a guarantee. A real home differs from any model — duct condition, sizing, installation quality, and how you actually live all move the number. The calculator's job is to get the physics and the economics right so the comparison is trustworthy; get a load calculation and a real quote before buying anything.

Built and maintained by the team at Liberty Air and Electric, a licensed Florida HVAC and electrical contractor. Weather tables rebuilt from the public archive; model constants documented in the engine source.