Putting Every Heating Fuel on One Energy Scale
Heating fuels are sold in units that refuse to be compared: gas by the therm, oil and propane by the gallon, firewood by the cord, pellets by the ton — and electricity by the kilowatt-hour. Before you can tell whether a heat pump would cost less than the oil boiler you already own, all of it has to land in a single unit. Converting the fuel's British thermal units into kilowatt-hours is the usual way to do that, because the kilowatt-hour is the one number already printed on a bill you receive every month.
What the Comparison Actually Needs
Energy Bought, Not Energy Delivered
Efficiency Differs Wildly by Appliance
Electricity Arrives Pre-Converted
Pricing a Winter's Heat Before You Switch Fuel
The goal is a cost per useful kilowatt-hour for each option, which you can then put beside your electricity tariff without any further translation.
Enter the BTU behind one purchase unit
Type the energy content of what you actually buy — 138 500 for a gallon of heating oil, 20 000 000 for a cord of seasoned hardwood. Spaces used as thousands separators are ignored, so long numbers stay readable while you type.
Divide the delivered price by the kWh result
A $3.60 gallon of oil that converts to 40.59 kWh costs 8.9 cents per kilowatt-hour of fuel energy. Multiply by the boiler's efficiency to get the cost of heat that reaches the rooms.
Run it backwards for an appliance nameplate
The swap arrows reverse the pair when you start from electricity instead — useful for asking how many BTU per hour a 3 kW heater delivers, or how a resistance panel compares with a gas insert.
Send the figure to your comparison sheet
Copying a field hands over the digits only, so each fuel drops into its own row of a spreadsheet without a unit label to clean out first.
Heating Fuels: Purchase Unit, BTU Content, kWh Equivalent
Each row takes one thing you can buy, its usual energy content, the kilowatt-hours that represents, and what survives at a typical appliance efficiency. Fuel energy content varies with grade and season, so treat these as planning figures.
| What you buy | Energy content (BTU) | Equivalent (kWh) | Useful kWh at typical efficiency |
|---|---|---|---|
| 1 therm of natural gas | 100,000 | 29.31 | 26.96 at 92 % |
| 1 gallon of #2 heating oil | 138,500 | 40.59 | 34.50 at 85 % |
| 1 gallon of kerosene | 135,000 | 39.56 | 33.63 at 85 % |
| 1 gallon of propane | 91,500 | 26.82 | 24.67 at 92 % |
| 1 cord of seasoned hardwood | 20,000,000 | 5,861 | 4,103 at 70 % |
| 1 ton of wood pellets | 16,500,000 | 4,836 | 3,869 at 80 % |
| 1 kWh, resistance heat | 3,412 | 1.00 | 1.00 at 100 % |
| 1 kWh, heat pump at COP 3 | 3,412 | 1.00 | 3.00 |
The last two rows are the reason the arithmetic surprises people. Every fuel in the table loses something between the tank and the room, while a heat pump moves more heat than the electricity it consumes — so a kilowatt-hour of electricity can be worth three kilowatt-hours of delivered warmth even though a kilowatt-hour of propane can only ever be worth less than one.
Built for a Fuel-Cost Comparison
Fuel Tickets and Meter Readings Both Ways
Start from a delivery ticket in BTU or from a bill in kilowatt-hours; whichever field you type in becomes the driver, and the swap arrows settle the direction for good.
Numbers That Drop Into a Cost Sheet
Each field has a copy control above it that hands over digits with nothing attached, so a row of fuel options can be assembled without editing every paste.
Reach the Joule and Watt-Hour Columns
Both dropdowns search across all 23 energy units, which is handy when an installer's brochure quotes kilojoules or a European appliance is rated in watt-hours.
Million-BTU Cordwood Stays Readable
Whole-season quantities run into eight and nine digits. Thousands are spaced out for legibility, and anything past ten digits is shown in scientific notation rather than truncated.
Questions Homeowners Ask When Comparing Fuels
What does AFUE do to the kilowatt-hours I calculated?
Annual fuel utilisation efficiency is the share of the fuel's energy that ends up as heat in the house across a whole season, flue and cycling losses included. Multiply the converted kilowatt-hours by it: a therm that converts to 29.31 kWh is worth 26.96 kWh in a 92 % AFUE condensing furnace, but only 23.45 kWh in an 80 % unit. That single number is often the difference between two fuels looking equal and one clearly winning.
Why does a heat pump beat baseboard heaters on the same kilowatt-hour?
A resistance element turns electricity into heat, and one kilowatt-hour can never become more than one kilowatt-hour of warmth. A heat pump does not make heat, it moves heat that is already outdoors, so the same kilowatt-hour can deliver two to four times as much. At a seasonal coefficient of performance of 3 the electricity you pay for buys about 10 200 BTU rather than 3 412 — which is why electric heating can be cheap or ruinous depending entirely on which box is fitted.
How many kilowatt-hours does an 80,000 BTU furnace use in an hour?
An 80,000 BTU nameplate is an input rate of 80,000 BTU per hour, which converts to 23.45 kWh of fuel energy for every hour the burner is actually firing. At 92 % efficiency about 21.6 kWh of that reaches the house. Furnaces rarely run flat out for a full hour, though, so an honest daily estimate needs run-time as well — a unit cycling half the time on a cold day burns roughly 280 kWh of gas energy over 24 hours.
How do I turn a fuel-oil delivery into kilowatt-hours?
Multiply the gallons on the ticket by 138,500 BTU, then convert. A 250-gallon top-up is 34,625,000 BTU, or about 10,148 kWh of fuel energy — near 8,625 kWh of delivered heat through an 85 % boiler. Divide the invoice total by that last figure and you finally have a number that sits directly beside the per-kWh rate on your electricity bill.
Why is BTU/h not the same thing as BTU?
BTU is a quantity of energy; BTU per hour is a rate, the speed at which an appliance delivers it. Appliance nameplates almost always carry the rate, and mistaking one for the other is the classic error in these calculations. The electrical parallel is exact: kilowatts are the rate, kilowatt-hours the amount. Convert the rate and you get kilowatts; convert the amount and you get kilowatt-hours.
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