Home Heating Fuel Cost Calculator

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Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

MMBtu: One million British thermal units, a common way to compare heat from different fuels.

Delivered heat: The useful heat that reaches the home after the heating equipment loses some energy.

Cost per delivered MMBtu: The yearly fuel cost divided by delivered heat, shown as dollars for each useful MMBtu.

Therm: A natural gas billing unit equal to 0.1 MMBtu.

CCF: One hundred cubic feet of natural gas. This calculator uses 0.1037 MMBtu per CCF, but the exact heat content can vary by utility.

Heat delivered to your home: The efficiency percent you enter. For furnaces and boilers, this is often AFUE. For heat pumps, it can be above 100 percent.

Fixed fees: Yearly fuel charges that do not change with the amount used, such as tank rental or a delivery membership.

Mistake: Entering a monthly amount in Fuel 1 yearly fuel used.
Fix: Use the total for the last 12 months, or add all deliveries for the year before entering Fuel 1 yearly fuel used.

Mistake: Mixing price units in Fuel 1 price, such as entering a monthly bill instead of $ per selected fuel unit.
Fix: Enter Fuel 1 price as dollars per therm, CCF, gallon, or kWh to match Fuel 1 type and bill unit.

Mistake: Using the wrong percent in Fuel 1 heat delivered to your home.
Fix: Enter the equipment efficiency percent, such as AFUE for a furnace or boiler; use 100 for electric resistance heat and a higher percent only when you mean heat pump performance.

Mistake: Adding delivery membership or tank rental into Fuel 1 fixed fees when it is already included in Fuel 1 price.
Fix: Put a fee in Fuel 1 fixed fees only if it is not already part of the unit price.

Mistake: Comparing Fuel 2 yearly heating fuel cost with Fuel 1 yearly heating fuel cost when Fuel 2 delivered heat is much higher or lower.
Fix: Use Fuel with lower delivered heat price for a fuel-price comparison, and use annual cost gaps only when the entered yearly heat amounts are similar.

• The calculator estimates fuel cost only. It does not include equipment purchase, repairs, rebates, financing, chimney work, duct changes, or comfort differences.
• Fuel heat content is treated as a fixed average. Real natural gas heat content can vary by utility, and delivered fuel quality can vary.
• Efficiency is user-entered and simplified as one yearly percent. Heat pump performance can change with outdoor temperature and equipment settings.
• Fuel 2 minus Fuel 1 yearly heating fuel cost is based on the yearly usage amounts you enter. If the two fuels do not deliver about the same heat, the yearly cost gap is not a like-for-like heat comparison.
• Months to spread the cost over only changes the monthly display. It does not change yearly cost or cost per delivered MMBtu.
• Fixed fees should be entered only when they are not already included in the unit price. Double-counting fees will overstate cost.

How the fuel comparison is calculated

The calculator first converts the entered fuel use into source heat in MMBtu, then applies the entered efficiency percent to estimate useful delivered heat. This is the standard idea behind comparing fuels by heat content instead of by gallon, therm, CCF, or kWh price alone [1][2].

Heat content used: natural gas therm, 0.1 MMBtu per therm; natural gas CCF, 0.1037 MMBtu per CCF; No. 2 heating oil, 0.1385 MMBtu per gallon; propane, 0.091333 MMBtu per gallon; electricity, 0.003412141633 MMBtu per kWh. One MMBtu is 1,000,000 Btu.

source_mmbtu = usage * heat_content_mmbtu_per_unit

delivered_mmbtu = source_mmbtu * (efficiency_percent / 100)

annual_cost = usage * unit_price + fixed_fee

monthly_cost = annual_cost / season_months

cost_per_delivered_mmbtu = annual_cost / delivered_mmbtu

In compare mode, the calculator keeps signed gaps so lower Fuel 2 costs show as negative numbers.

delivered_heat_price_gap = fuel2_cost_per_delivered_mmbtu - fuel1_cost_per_delivered_mmbtu

annual_cost_gap = fuel2_annual_cost - fuel1_annual_cost

Worked mini-example

If Fuel 1 is 800 therms of natural gas at $1.50 per therm, 95 percent efficiency, and $120 in fixed fees, the source heat is 80 MMBtu and the delivered heat is 76 MMBtu. The yearly cost is $1,320, the cost per delivered MMBtu is $17.37, and spreading the cost over 6 months gives $220 per chosen month.

If Fuel 2 is 600 gallons of heating oil at $4.00 per gallon and 85 percent efficiency with no fixed fee, its delivered heat is 70.635 MMBtu and its cost per delivered MMBtu is $33.98. Fuel 2 minus Fuel 1 is $16.61 per delivered MMBtu and $1,080 per year, so Fuel 2 is higher on both measures in that example.

Input checks

Usage and efficiency must be greater than 0, efficiency cannot be above 500 percent, prices and fixed fees cannot be negative, and months must be a whole number from 1 to 12. Conventional comma grouping such as 12,000 is accepted, but malformed commas such as 1,20 are rejected so the number is not misread.