How to use the heating fuel cost per million btu calculator
- Enter the heat needed per year in million BTU, or leave the example and read the cost per million BTU alone.
- List each fuel with its price per unit, the unit (therm, gallon, kWh), the BTU per unit and the efficiency in percent. The example rows are values you should replace.
- For a heat pump, enter the seasonal COP times 100 as the efficiency: a COP of 3 is 300.
- Read the lowest-cost fuel, then the table with the cost per million BTU, the ratio to the lowest and the cost of your yearly heat.
Formula
delivered BTU per unit = BTU per unit x efficiency / 100
units per million BTU = 1,000,000 / delivered BTU per unit
cost per million BTU = price per unit x units per million BTU
yearly cost = cost per million BTU x million BTU needed per year
Efficiency above 100 percent is allowed only for heat pumps, whose COP counts heat moved as well as electricity used.
Five fuels at example prices
Natural gas at $1.50 per therm (100,000 BTU) and 95 percent efficiency costs $1.50 / (100,000 x 0.95) x 1,000,000 = $15.79 per million BTU. Propane at $2.60 per gallon, 91,452 BTU and 95 percent costs $29.93. Heating oil at $3.80, 138,500 BTU and 85 percent costs $32.28.
Electric resistance heat at $0.16 per kWh (3,412 BTU) and 100 percent costs $46.89. A heat pump with a COP of 3 at the same price costs $15.63, about the same as gas. For 60 million BTU a year those come to $947.37 for gas, $937.87 for the heat pump and $2,813.60 for resistance heat.
Why compare by delivered heat
A gallon of oil, a therm of gas and a kilowatt-hour of electricity cannot be compared by price alone, because each holds a different amount of energy and each heating system turns a different share of it into heat in your rooms. Converting everything to the cost of one million BTU of delivered heat puts them on the same footing. It also shows how large the gain from a heat pump is: it moves more heat than the electricity it uses, so its cost per million BTU falls in proportion to its COP.
For one appliance at a time, the electric vs gas appliance calculator and the gas heating cost calculator go into more detail. The electricity cost calculator prices a single load.
What the comparison does not include
Equipment price, installation, maintenance, fixed monthly fees, delivery minimums, taxes and rebates are not in these numbers. Heat pump efficiency falls in very cold weather, and furnace efficiency depends on age and sizing, so use a seasonal figure from your equipment data. Heat content per unit is a physical property that suppliers publish, and the values in the example rows are common reference values to be checked against your invoice. Prices are yours to enter and change from month to month.
Assumptions and limits
- Prices, heat contents and efficiencies in the example rows are examples. Replace them with values from your own bills and equipment.
- Efficiency is a seasonal average for the whole system, including distribution losses, expressed in percent.
- One BTU of delivered heat is worth the same whichever fuel supplied it. Comfort, noise and air quality are not compared.
- Costs are for energy only. Fixed charges, taxes and fees are not included.
Frequently asked questions
What is a therm?
A therm is 100,000 BTU, a unit natural gas is often billed in. Some bills use hundred cubic feet (ccf) or cubic meters instead; convert with the heat content printed on the bill, then enter it per unit.
How do I enter a heat pump?
Use electricity as the unit, 3,412 BTU per kWh, and enter the seasonal COP times 100 as the efficiency. A seasonal COP of 3 means 300 percent. Use a seasonal figure for your climate, not a laboratory rating.
Why is electric resistance heat so much more expensive?
It turns each kWh into exactly one kWh of heat (3,412 BTU). A therm of gas in a 95 percent furnace delivers about 95,000 BTU, which equals about 28 kWh, so at the example prices that heat costs $1.50 from gas and about $4.45 from electricity.
Can I compare wood or pellets?
Yes. Add a row with the price of a cord or ton, the BTU per unit from the seller, and the efficiency of your stove. The result is on the same per-million-BTU basis as the others.