Transparency

Methodology & data sources

Electricity rates

PowerCostAtlas uses residential average retail electricity prices from the U.S. Energy Information Administration (EIA), Electricity Sales to Ultimate Customers data series. The current local snapshot is July 2026.

Monthly rate history

The scheduled EIA sync also stores up to 24 recent monthly residential price observations for the U.S. average and each of the 50 states. State pages use those observations to calculate historical highs, lows and year-over-year changes. Historical values describe published averages; they are not forecasts.

Basic electricity-cost calculation

Energy used is power in kilowatts × time in hours. Cost is energy used in kWh × electricity price per kWh. The calculator converts the EIA rate from cents to dollars automatically.

GPU specifications

GPU pages use manufacturer-published reference power specifications and link directly to the source page. NVIDIA pages use Total Graphics Power (TGP); AMD pages use Typical Board Power (TBP). Those metrics describe the graphics card and should not be interpreted as the computer's measured wall draw.

Gaming-PC reference model

The GPU calculator keeps the vendor power specification separate from model assumptions. The default reference uses 80% of rated graphics power, 150 W of additional internal system load, and 90% PSU efficiency. Estimated wall draw equals the modeled internal load divided by PSU efficiency. Every assumption is adjustable. The defaults are not benchmark measurements or vendor claims.

HVAC models

HVAC pages use three transparent model types. Electric resistance pages begin with direct electrical input watts. Cooling pages convert Btu/h capacity and CEER or EER2 into approximate active electrical input. Heat-pump heating pages convert delivered Btu/h into thermal kilowatts and divide by coefficient of performance (COP). An adjustable active/cycling percentage then models part-time operation before runtime is converted into kWh.

HVAC efficiency sources

Definitions and reference efficiency concepts are based on U.S. Department of Energy and ENERGY STAR material. ENERGY STAR defines EER2 as cooling output divided by electrical input at rating conditions, and COP as delivered heating rate divided by electrical input. Room-air-conditioner pages use CEER in the same Btu-per-watt-hour style. Every efficiency input remains editable because actual systems and operating conditions vary.

EV models

EV driving-cost pages use kWh per 100 miles and annual mileage, then add an adjustable charging-loss assumption before applying the electricity rate. Charge-session pages use battery size, state-of-charge window, charging losses, and charger power.

EV charging references

Level 1 and Level 2 terminology and charging-power context are based on U.S. Department of Energy AFDC and FEMP material. Actual vehicle and EVSE limits vary, so charger power remains editable.

Water-heating models

Water-heating pages calculate the thermal energy needed to raise a daily volume of water by a selected temperature difference. The thermal load is converted from Btu to kWh and divided by a user-editable effective factor to estimate grid electricity. This effective-factor model is intentionally simpler than the federal Uniform Energy Factor (UEF) laboratory test and is not presented as a certified product rating.

Water-heating references

Water-heater definitions and efficiency context are based on U.S. Department of Energy material. Heat-pump water heaters move heat rather than generating all heat directly, which is why their effective performance factor can exceed 1. Product-specific EnergyGuide and manufacturer data should be used when evaluating a purchase.

Pool-pump models

Pool-pump pages price one or two daily operating settings from electrical input watts and runtime. The variable-speed comparison does not hard-code a universal savings percentage; users enter the power and hours for each schedule. ENERGY STAR guidance is used for context on why lower-speed filtration can reduce energy use.

What is not included

State averages do not capture a household's exact utility plan. Fixed monthly fees, taxes, demand charges, tiers, seasonal tariffs and time-of-use prices are not included unless the user accounts for them separately. PC power varies by workload and hardware. HVAC consumption varies with weather, building load, equipment sizing, ducts, airflow, thermostat behavior, defrost cycles, backup heat and maintenance.

Update policy

A scheduled GitHub Actions workflow checks the EIA API for newly published monthly residential rates. When the dataset changes, the repository updates the latest-rate snapshot and the 24-month history file, then the hosting platform rebuilds the static site. Manufacturer GPU specifications and HVAC, water-heating, and pool-pump methodology references are reviewed when those sections are added or materially updated.

Automated content

Rate comparisons, example costs, rankings and calculator outputs are generated programmatically from cited datasets, vendor specifications and displayed assumptions. Automation is used so that the same calculation method is applied consistently when EIA values change.

Source attribution

Electricity-rate source: U.S. Energy Information Administration. GPU power specifications are sourced from NVIDIA and AMD product pages linked on each GPU calculator. HVAC, water-heating, and pool-pump definitions and reference criteria link to ENERGY STAR and U.S. Department of Energy pages. PowerCostAtlas is an independent project and is not endorsed by or affiliated with those organizations.