Methodology & Data Sources

Every rate, cost and comparison on this site is derived from published US Energy Information Administration data and a small set of stated assumptions. This page lists all of them so you can check our arithmetic — or decide our assumptions do not match your home.

Where the prices come from

All energy prices are US residential averages published by the EIA. We do not use utility marketing rates, brokered supply offers or third-party aggregators.

The physics we use

These are fixed conversions, not opinions. They are what let us compare a gas furnace to a heat pump to a space heater on the same basis: dollars per unit of heat actually delivered into the room.

Electric resistance heaters are all the same efficiency

This one matters, because a lot of heater marketing depends on you not knowing it. Every electric resistance heater — ceramic, oil-filled radiator, infrared panel, convection, baseboard — converts essentially 100% of the electricity it draws into heat. There is nowhere else for the energy to go. Two 1,500 W heaters of different types, holding the same room at the same temperature, use the same amount of electricity and cost the same to run.

What genuinely differs between them is how the heat is delivered: an oil-filled radiator stores heat and releases it gradually, so room temperature swings less; an infrared panel warms surfaces and people directly, which feels warm sooner and works better in a draughty space. Those are real reasons to prefer one over another. Lower energy consumption at the same setpoint is not, and you will not find that claim anywhere on this site.

Heat pumps are the genuine exception. They move heat rather than generating it, so they deliver more heat energy than the electrical energy they consume.

Assumptions we chose

Everything below is our own modelling choice rather than a published figure. Reasonable people could pick different numbers, and if yours differ, every calculator on the site lets you type your own.

Equipment efficiency

The heat pump figures are ours. ENERGY STAR describes air-source heat pumps as delivering “up to three times” the energy they consume; both capacity and COP fall as it gets colder outside, which is why our figure scales with climate rather than sitting at a flat 3.0. A COP of 4 or more is achievable, but at mild outdoor temperatures — that is, not when you need the heat most.

Whole-home heating load

Monthly heating cost figures assume the home’s full heating load is met by the system in question. We model energy as heat loss coefficient × heating degree days × 24 hours, with a 65°F degree-day base and these round engineering values for the heat loss coefficient:

This models one identical, average-insulated house in every state, which is what makes state-to-state comparison meaningful — but it means our monthly figures generally run above EIA’s national household averages, because real households heat fewer rooms, set back thermostats, and live in homes of every size and vintage. Read our numbers as “the same house, priced in different places”, not as a forecast of your bill.

Heater sizing

We size portable heaters at roughly 10 watts per square foot for an average-insulated room, so a 1,500 W heater suits about 150 sq ft. Manufacturer “coverage” figures are routinely five to ten times higher than this. A 1,500 W heater produces about 5,100 BTU/hr no matter what the box says, and a 120 V household outlet cannot supply more than 1,500 W, so no portable plug-in heater heats a large room. Where we quote a manufacturer’s coverage number, we label it as theirs and show the sizing-rule figure beside it.

Known limitations

We would rather tell you these than have you find them.

• No fixed charges or tariff structures. Our figures are energy cost only. Your bill also carries standing charges, delivery fees and taxes, and may use tiered or time-of-use pricing. Those can move the total substantially — especially at low usage.
• State averages hide large in-state variation. Two households in the same state on different utilities can pay very different rates. Your own bill beats our state figure every time, and every calculator here accepts it.
• Some state gas prices are estimated. EIA withholds the winter residential gas price for a few states. Where that happens we fall back to the national winter average and label the figure as estimated on the page. Currently affected: Florida, Louisiana, Maine, Maryland, Minnesota, New Mexico.
• Winter temperature normals are approximate. They come from station normals for a representative location, not a state-wide weighted average. Large or mountainous states vary enormously internally.
• We do not model federal tax credits. The §25C Energy Efficient Home Improvement Credit and the §25D Residential Clean Energy Credit both ended for property placed in service after 31 December 2025, so no payback figure on this site assumes one. Check current federal, state and utility incentives yourself before buying — they change, and state and utility programs still exist in many places.
• Equipment purchase and installation prices are not our data. Where we quote them we cite ENERGY STAR or DOE. They vary hugely by region and contractor.

How this data gets maintained

Every price on this site lives in one file, so a refresh updates the whole site at once rather than page by page. It was last refreshed on August 22, 2026.

EIA’s release schedule sets the pace: the Electric Power Monthly lands around the 26th of each month, the Natural Gas Monthly at month end, and the propane and heating oil surveys restart in October. The Winter Fuels Outlook is published each October.

Across the 51 jurisdictions we cover — 50 states plus the District of Columbia — residential electricity currently runs from 12.35¢/kWh in Idaho to 52.00¢/kWh in Hawaii, a spread of more than four to one. That spread is why a national average is a poor guide to your own cost, and why the state pages exist.

Found something that looks wrong? Tell us — a specific correction with a source is genuinely useful and we would rather fix it than defend it.