Transparency
Data Sources & Assumptions
Dwellvance calculators use published energy data, documented conversion factors, user-provided information, and stated assumptions to produce planning-level estimates. The sections below document the heat pump calculator's inputs first, followed by the sources behind the solar calculator.
Electricity Rates
Default residential electricity rates are based on state-level data from the U.S. Energy Information Administration (EIA). State-average residential prices are used as reference values rather than representing a homeowner's exact utility tariff.
Source
U.S. Energy Information Administration — Electric Power Monthly, Table 5.6.A, Average Price of Electricity to Ultimate Customers by End-Use Sector, by State.
View the EIA electricity-rate dataUpdate frequency: monthly. Data sources documentation was last verified in September 2026.
When a homeowner provides an electricity-rate override, the calculator uses that value instead of the state default. If no verified state rate is available, the calculator does not invent a rate.
Energy Conversion Factors
Different heating fuels are converted into a common energy unit using documented EIA conversion factors.
| Energy source | Unit | BTU per unit |
|---|---|---|
| Electricity | kWh | 3,412 |
| Natural gas | therm | 100,000 |
| Heating oil | gallon | 138,500 |
| Propane | gallon | 91,452 |
Source: U.S. Energy Information Administration, British Thermal Units (Btu).
View the EIA BTU referenceHow the Data Is Used
The calculator converts reported annual heating energy use into BTUs, adjusts the energy input using the existing heating system's efficiency, and estimates the useful heat delivered to the home.
The estimated useful heat requirement is then used with the selected heat pump performance input to estimate electricity consumption and operating cost.
This separates sourced real-world inputs from values calculated by the application.
Solar Calculator Sources
The solar calculator's production estimates are informed by NREL's PVWatts, and its planning-level installation cost estimates reference U.S. Department of Energy solar cost benchmarks. You can replace the cost benchmark with a known project cost, and savings and payback require an electricity rate.
The full solar approach is described on the solar methodology page.
Verification & Data Provenance
Dwellvance is designed so that important real-world values can be traced to their source, geographic scope, units, and applicable dates where those details are available.
External data should be reviewed periodically because electricity rates and other source values can change over time.
Data Sources Last Verified: September 2026
Limitations
- State-average electricity prices may differ from a homeowner's utility-specific rate.
- Actual energy costs depend on weather, home characteristics, equipment performance, and operating behavior.
- Fuel prices, installation costs, incentives, and equipment performance can change over time.
- Calculator results are estimates rather than guaranteed savings or actual project costs.
Explore the Methodology
For a fuller explanation of the calculation process, inputs, assumptions, and limitations, see the Dwellvance methodology.
Read the calculation methodology →