How the estimates work

Last checked 7th Oct. 2026. Every input comes from a public source listed below, and the full calculation runs in your browser, so you can check it.

Water heaters, heat pumps, furnaces and central AC

Source: NREL's Residential Efficiency Measures Database (REMDB). The National Renewable Energy Laboratory publishes quantile regressions of retail equipment prices against size and efficiency, built from retailer and distributor prices, RSMeans, DOE rulemaking documents and other sources, in 2023 dollars. For each piece of equipment it also gives an installation multiplier or adder for a "retrofit", which includes removing the old equipment. We use the release of 23rd Dec. 2024.

For each estimate:

Equipment price = intercept + coefficient 1 x metric 1 + coefficient 2 x metric 2, for REMDB's 10th, 50th and 90th percentile regressions. The metrics are, for example, tons and SEER for a heat pump, or UEF and gallons for a tank water heater.
Installed cost = equipment price x retrofit multiplier + retrofit adder. Labor is the installed cost minus the equipment price.
Your state: the labor part is multiplied by your state's median hourly wage for the trade (HVAC technicians or plumbers) divided by the US median, from the Bureau of Labor Statistics' Occupational Employment and Wage Statistics, May 2025. Equipment is priced nationally.
Today's dollars: everything is multiplied by 1.099, the change in the Consumer Price Index (CPI-U, all items) from the 2023 average to August 2026.

The typical figure is the 50th percentile; the range spans the 10th to 90th. When a size or efficiency falls outside the range a regression was fitted on, the calculator prices the nearest value inside that range and says so. (REMDB's own guidance is to use only the middle regression there; we clamp instead, because extrapolating far outside the data gives prices no real product has.)

Solar

Price per watt: Berkeley Lab, Tracking the Sun 2024 Edition: median installed price of host-owned residential systems installed in 2023, before incentives, nationally ($4.2 per watt) and for 21 states with at least 20 systems in the data. The range uses the national 20th and 80th percentiles ($3.2 and $5.5). All are converted to today's dollars with the same CPI factor.
Output: NREL's PVWatts (version 8) for each state's largest city: 1 kW of standard panels on a fixed roof mount facing south at a 20 degree tilt, with PVWatts' default 14% system losses.
Power price: EIA Electric Power Monthly, table 5.6.B, average residential price by state, year to date through July 2026.
Size = yearly kWh to cover / kWh per kW. Savings = yearly output x power price. Payback = cost / savings. Payback ignores financing, degradation, maintenance and changes in power prices, and assumes full net metering.

Sources

NREL, National Residential Efficiency Measures Database (machine-readable file, Dec. 2024).
U.S. Bureau of Labor Statistics, Occupational Employment and Wage Statistics, May 2025: occupations 49-9021 (HVAC mechanics and installers) and 47-2152 (plumbers).
U.S. Bureau of Labor Statistics, Consumer Price Index, CPI-U all items, August 2026.
Berkeley Lab, Tracking the Sun, 2024 Edition.
NREL, PVWatts Calculator, version 8.
U.S. Energy Information Administration, Electric Power Monthly.
IRS, Energy Efficient Home Improvement Credit and Residential Clean Energy Credit.

Limits

REMDB is a national database; it does not know your house. Prices for the same job vary with access, the condition of venting, wiring and ducts, permits and the contractor. Some REMDB regressions rest on few data points; NREL rates each one, and we leave out equipment where the data looked unreliable to us. We update the data when a source publishes a new edition.