Methodology
Transparent formulas and public-source defaults.
WattNomic keeps assumptions visible so users can replace defaults with their bill, quote, or local data.
Electricity rates
Residential electricity defaults are extracted from U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A for February 2026. The EIA value is an average price in cents per kilowatthour, not a quote from a specific utility.
Electricity bill formula
Monthly cost = monthly kWh multiplied by cents/kWh divided by 100, plus fixed monthly charges.
Solar payback formula
Annual value = system size multiplied by annual production per kW, electricity price, and bill offset. Simple payback = installed cost divided by annual value.
Heat comparison formula
The heating calculator compares estimated cost per million BTU of delivered heat using common energy conversion factors and user-entered equipment assumptions.
What to verify locally
Before making a purchase decision, confirm utility tariffs, fixed fees, net-metering rules, local incentives, equipment sizing, contractor quotes, and installation constraints.