Gas vs Electric Heating Cost Calculator

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Table of contents

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

BTU: British thermal unit, a small amount of heat energy. Heat needed (BTU per hour) is the useful heat delivered each hour.

Therm: A natural gas billing unit equal to 100,000 BTU of energy before furnace efficiency is applied.

kWh: Kilowatt-hour, the unit used on most electric bills. The calculator uses 3,412 BTU per kWh for energy conversion.

COP: Coefficient of performance. It tells how many units of heat a heat pump delivers for 1 unit of electricity. COP 3 means about 3 units of heat for 1 unit of electricity.

Gas furnace efficiency: The percent of gas energy that becomes useful heat in the home. It is often called AFUE for furnaces and boilers.

MMBTU: One million BTU. Cost per MMBTU puts gas and electric heat on the same useful-heat scale.

Electric cost minus gas cost: A signed cost gap. Positive means electric heat costs more for the month. Negative means electric heat costs less.

Mistake: Entering Heat needed (BTU per hour) as total monthly BTU.
Fix: Use a per-hour heating rate for Heat needed (BTU per hour), then put the month total in Heating time (hours per month).

Mistake: Using cents instead of dollars for Electricity price ($ per kWh).
Fix: Enter 16 cents as 0.16 in Electricity price ($ per kWh), not 16.

Mistake: Typing a gas bill total into Natural gas price ($ per therm).
Fix: Use the rate per therm for Natural gas price ($ per therm), not the whole monthly bill.

Mistake: Picking Custom heat pump COP but leaving Custom heat pump COP at a guess that does not match your system.
Fix: Use Electric heating type presets when you do not know COP, or enter a seasonal value in Custom heat pump COP if you have one.

Mistake: Entering Gas furnace efficiency (percent) as a decimal.
Fix: Enter 80 for Gas furnace efficiency (percent), not 0.80.

Mistake: Adding Extra gas account charge ($ per month) when you would keep gas service for cooking, water heating, or another use.
Fix: Leave Extra gas account charge ($ per month) at 0 unless switching heating would let you cancel that charge.

• This is an operating cost comparison only. It does not include equipment purchase price, installation, maintenance, repairs, rebates, taxes, or financing.
• Heat pump COP changes with outdoor temperature, system design, defrost cycles, and backup heat use. A single COP is a simplified average.
• Use delivered energy prices when possible. Bill totals can include fixed fees, taxes, and tiered rates that may not match the next unit of energy you use.
• Extra gas account charge ($ per month) should be used only when heating is the only reason you keep gas service and the charge would truly go away.
• The calculator assumes both systems deliver the same useful heat. It does not check whether a heater is large enough for your coldest hour.
• Gas furnace efficiency (percent) is treated as a constant monthly efficiency, even though real systems can lose efficiency from duct losses, cycling, or poor maintenance.
• Zero Heating time (hours per month) gives zero monthly energy use. Break-even results may be less useful because there is no heating load to compare.

How the comparison is built

The calculator first finds the same useful heat amount for both systems. Useful heat means heat delivered to the home, not fuel energy before losses.

useful_heat_btu = heat_output_btu_hr * heating_hours_month

Gas cost uses 100,000 BTU per therm and the entered Gas furnace efficiency (percent). If an Extra gas account charge ($ per month) is entered, it is added to the gas side.

gas_monthly_cost = useful_heat_btu / (100000 * gas_efficiency_percent / 100) * gas_price_therm + extra_gas_account_charge

Electric cost uses 3,412 BTU per kWh. Electric resistance heat uses COP 1. Heat pump presets use COP 2 or COP 3, and Custom heat pump COP is used only when that option is selected.

electric_monthly_cost = useful_heat_btu / (3412 * electric_cop) * electricity_price_kwh

The signed gap keeps the direction clear. A positive number means electric heat costs more. A negative number means electric heat costs less.

monthly_cost_gap = electric_monthly_cost - gas_monthly_cost

Break-even results

The break-even electricity price answers this question: at the selected electric COP, what $ per kWh would make electric heat cost the same as gas?

break_even_electric_price = gas_monthly_cost / (useful_heat_btu / (3412 * electric_cop))

The COP needed to match gas answers this question: at the entered electricity price, how efficient would a heat pump need to be to tie the gas cost?

cop_needed_to_match_gas = (useful_heat_btu / 3412 * electricity_price_kwh) / gas_monthly_cost

If gas monthly cost is zero, the COP needed is shown as N/A instead of dividing by zero.

Cost per useful heat

Cost per million BTU converts each monthly cost to the same useful-heat unit, so a small room and a large home can still be compared on a fuel-cost basis.

cost_per_mmbtu = monthly_cost / (useful_heat_btu / 1000000)

Mini example

With Heat needed (BTU per hour) of 40,000, Heating time (hours per month) of 240, Natural gas price ($ per therm) of $1.25, Electricity price ($ per kWh) of $0.16, Electric heating type set to electric resistance, and Gas furnace efficiency (percent) of 80, useful heat is 9,600,000 BTU. Gas heating cost is $150.00, electric heating cost is about $450.18, and Electric cost minus gas cost is about $300.18, so gas is cheaper for that month.