Estimate the cost to run an electric, natural gas, or propane garage heater by hour, day, month, and year.
Table of contents
How to use our Garage Heater Running Cost Calculator
- Choose Heater fuel type so the calculator shows the matching heater size and energy price fields.
- Enter Electric heater power, Gas heater input rating, or Propane heater input rating from the heater label, using watts or Btu/h as shown.
- Enter Heater time available, Use days, and Heater actually runs to describe how long the heater is allowed to run and how often it fires.
- Enter Electricity price, Natural gas price, or Propane price from your bill or delivery receipt, then select Calculate.
- Sanity-check Estimated energy used each month against your bill units; a very high number usually means the heater size, run percent, or price unit was entered wrong.
Definitions
Heater fuel type: The energy source the garage heater uses: electricity, natural gas, or propane.
Electric heater power: The watt rating on an electric heater label. A higher watt number uses more electricity each running hour.
Input rating: The fuel energy a gas or propane heater consumes each hour, usually printed as Btu/h on the heater label.
Heater time available: The number of hours per day the heater is on, enabled, or allowed to run.
Heater actually runs: The percent of available time the heater is fully firing or drawing full power. This accounts for thermostat cycling.
kWh: Kilowatt-hour, the electricity billing unit used for electric heaters.
Therm: A natural gas billing unit equal to 100,000 Btu.
Full-power running hour: One hour when the heater is actively using its full rated input.
Common mistakes and quick fixes
Mistake: Entering amps or volts in Electric heater power instead of watts.
Fix: Use the watt rating on the label, or multiply volts by amps first and enter that watt value in Electric heater power.
Mistake: Using heater output Btu/h for Gas heater input rating or Propane heater input rating.
Fix: Use the input rating from the heater label because the cost is based on fuel burned, not heat delivered.
Mistake: Treating Heater time available as the hours the burner or element is fully on.
Fix: Enter the hours the heater is allowed to run in Heater time available, then use Heater actually runs for thermostat cycling.
Mistake: Typing 0.50 in Heater actually runs when you mean 50 percent.
Fix: Enter 50 in Heater actually runs for half-time operation, or 100 for a full-power estimate.
Mistake: Mixing up Natural gas price and Propane price units.
Fix: Enter Natural gas price in $ per therm and Propane price in $ per gallon; do not enter a total bill amount unless it is already divided by those units.
Mistake: Reading Estimated yearly heater cost at this pace as a winter-only forecast.
Fix: Treat Estimated yearly heater cost at this pace as the daily pattern multiplied by 365 days, not as a weather-based heating season model.
Limitations & Key Assumptions / Boundary Conditions
- The estimate uses the selected heater input or power rating. It does not model garage size, insulation, air leaks, outdoor temperature, warm-up time, or thermostat setpoint.
- Gas and propane estimates use fuel input, not delivered heat. Heater efficiency affects how much heat reaches the garage, but the fuel cost is still based on input fuel burned.
- Utility bills can include fixed fees, taxes, minimum charges, delivery charges, meter fees, and tiered rates. Those items may make the bill different from the simple energy-price estimate.
- Use days sets the monthly estimate directly. A month with more or fewer actual use days will change Estimated monthly heater cost.
- Estimated yearly heater cost at this pace is a 365-day scale-up of the entered daily pattern. It is not a seasonal weather forecast.
- Hidden fuel fields are ignored. For example, propane price does not affect results when Heater fuel type is Electric.
Methodology
Calculation method
The calculator first converts the selected heater size into fuel used for one full-power running hour. Electric heaters use watts converted to kilowatts. Natural gas heaters use therms, where 1 therm is 100,000 Btu. Propane heaters use 91,452 Btu per gallon, a standard fuel-property value listed by the Alternative Fuels Data Center [1].
electric_kwh_per_running_hour = electric_power_w / 1000
gas_therms_per_running_hour = gas_input_btu_per_hour / 100000
propane_gallons_per_running_hour = propane_input_btu_per_hour / 91452
Next, it adjusts the clock time by the percent of time the heater actually runs. A thermostat that cycles on half the time has a run percent of 50.
run_hours_day = hours_per_day * run_percent / 100
run_hours_month = run_hours_day * days_per_month
The selected fuel price is then multiplied by fuel used per running hour. The daily, monthly, and yearly cost estimates scale that running-hour cost by the adjusted run time.
cost_per_running_hour = fuel_used_per_running_hour * fuel_price
daily_cost = cost_per_running_hour * run_hours_day
monthly_cost = cost_per_running_hour * run_hours_month
yearly_cost = daily_cost * 365
fuel_used_month = fuel_used_per_running_hour * run_hours_month
Mini-example
For a 5,000 W electric garage heater, the full-power fuel use is 5,000 / 1,000 = 5 kWh per running hour. At $0.16 per kWh, one full-power running hour costs 5 * $0.16 = $0.80. If the heater is available 4 hours per day, used 30 days per month, and actually runs 50 percent of that time, the monthly full-power run time is 4 * 30 * 50 / 100 = 60 hours. The estimated monthly heater cost is 60 * $0.80 = $48.00, and the estimated energy used each month is 60 * 5 = 300 kWh.
Input handling
Only the fields for the selected Heater fuel type are used. Blank, zero, or negative heater size is an error because a heater with no input cannot have a running cost. Zero Heater time available, zero Use days, zero Heater actually runs, and zero energy price are allowed, so they can return zero cost. Heater actually runs must be from 0 to 100 percent.