One real figure times another, not a wattage guess

Every model page multiplies two sourced numbers: US EPA ENERGY STAR certified-product data, data.energystar.gov (src/data/appliances.csv), and EIA Electric Power Monthly, Table 5.6.B, residential, by state (src/data/rates-by-state.csv). That is real per-model energy use, not a nameplate wattage assumed to run continuously, which is where most generic "appliance cost calculator" pages go wrong.

The national-average rate, and what it actually is

The default rate on every page (18.8¢/kWh) is the simple mean of all 51 published state residential rates, not a population-weighted figure and not EIA's own published national average, which this site does not hold. It is disclosed as exactly that everywhere it appears. The state selector on every model page recomputes the real per-state figure from the same EIA table.

Category averages and the efficiency verdict

Mean/median annual kWh/yr across every currently-certified model in the category (src/data/category-stats.json), not an external benchmark. A model's "more efficient" or "less efficient" label compares it only to other currently-certified models in its own category, refrigerators against refrigerators, not against an outside benchmark or an older, uncertified baseline.

Lifespan, and the two categories with none

NAHB/Bank of America Home Equity Study of Life Expectancy of Home Components — see LIFESPAN_YEARS for which categories have a sourced figure. Freezers and dehumidifiers have no NAHB figure, so no lifetime-cost number is shown for them rather than a guessed one; every other category's lifetime figure is the model's own annual cost times the sourced lifespan.

A known limit: clothes dryers

ENERGY STAR's own combined annual energy-use figure for clothes dryers is not filtered to electric-only models the way this site's water heater data is. A small number of dryer listings are gas models, where ENERGY STAR's certification metric folds a converted gas-energy equivalent into the same kWh figure used here, which is not what a gas dryer owner's actual electric bill reflects. The public dataset does not carry a separate fuel-type field to filter on reliably, so this is disclosed rather than guessed at from model numbers, which vary by brand and are not reliable enough to sort on. Compare: the Bosch WQB245AXUC at 122 kWh/yr and the Amana NGD5800H** at 687 kWh/yr show the spread this produces.

See it applied

A worked example: the ABL AREF18** costs $68/year at the national-average rate, from 360 kWh/yr times 18.8¢/kWh divided by 100. For why the rate side of that math swings so much by state, see the guide to state rate differences; for when a lower running cost actually justifies buying new, see the guide to replacement math.