JouleIO Expertise & Methodology

How JouleIO energy calculators work — data sources, methods, editorial standards, update cadence.

Why this page exists

Energy decisions — solar install, heat pump upgrade, appliance replacement — can swing tens of thousands of dollars over a system's lifetime. When a calculator influences those decisions, you deserve to know where the numbers come from.

Primary data sources

EIA Electricity Data Browser
Average residential electricity rates ($/kWh) by state, monthly. Foundation for /electricity-cost/ and /energy-cost/ city-adjusted estimates.
EIA Residential Energy Consumption Survey (RECS)
Household energy use by appliance, climate zone, and home characteristics. Powers per-appliance kWh estimates.
NREL PVWatts Solar Calculator
Solar generation estimates by ZIP, panel orientation, and tilt. Source for /solar/ city-level production estimates.
DOE Energy Efficiency Data
Heat pump COP ratings, appliance efficiency standards, weatherization savings benchmarks.
EnergyStar Product Database
Certified appliance efficiency ratings (refrigerators, water heaters, HVAC). Used for /appliance/ comparison output.
NOAA Climate Data
Heating Degree Days (HDD) and Cooling Degree Days (CDD) by city for HVAC load estimation.

Calculation methodology

Appliance kWh per year
kWh = wattage × hours/day × 365 / 1000. We adjust standby vs active draw for electronics. RECS-weighted average use frequency by appliance type.
Solar payback period
System cost after state rebates and any verified tax credit divided by annual electricity savings (PVWatts production x local kWh rate). For new 2026 homeowner-owned systems, federal residential credit defaults to 0% unless eligibility is documented.
Heat pump operating cost
(HDD × home heat load BTU/HDD) / COP / 3412 = kWh/year for heating. Same for cooling using CDD. Higher COP = lower cost. We disclose COP varies with outdoor temp (cold-climate units perform better).
Electricity cost city-adjustment
State avg rate × city utility-specific multiplier when available, else state avg. Tier rates (CA, AZ) shown when applicable.

Editorial standards

All calculators run client-side. No address, ZIP, or utility account data transmitted off-device.
Electricity rate data shows EIA publication month on every calculator output.
Solar estimates show PVWatts model assumptions (panel orientation, tilt, derate factor).
Heat pump COP ratings cite specific test conditions (47°F vs cold-climate 17°F) per AHRI standard.
Articles cite primary sources (EIA, NREL, DOE, EnergyStar) — not utility marketing material or solar installer sales pitches.
We do not accept solar installer or utility company sponsorships that affect calculator output.

Update cadence

What	When
EIA electricity rates	Monthly (EIA-861 monthly state release)
EIA RECS appliance data	Quadrennial (every 4 years, last 2020 release)
NREL PVWatts model	Annual (NREL TMY3/4 weather data updates)
EnergyStar certifications	Quarterly (EPA refresh)
Federal residential energy credits	Annual + ad-hoc legislative changes (current 2026 default: no new residential 25D credit after Dec. 31, 2025)
Article fact-checks	Quarterly + within 14 days of major utility rate change >5%

Corrections and feedback

Email [email protected]. We respond within 14 days.

Who builds JouleIO

See /about/team/ for team backgrounds.