A BTU cost per hour calculator estimates how much an appliance costs to run from its heat output, fuel type, efficiency, and local energy rate. At typical U.S. prices, a 10,000-BTU-per-hour gas burner may use about $0.08-$0.16 of fuel per hour, while a 10,000-BTU-per-hour electric heater may cost about $0.35-$0.55 per hour.
The result depends on whether the listed BTU rating is fuel input or useful heat output. Utility rates, appliance efficiency, and actual run time can shift the estimate substantially.
| Item | Low | Average | High | Notes |
|---|---|---|---|---|
| Natural gas per 10,000 BTU input per hour | $0.06 | $0.10 | $0.16 | Based on $0.60-$1.60 per therm |
| Electric resistance heat per 10,000 BTU per hour | $0.35 | $0.42 | $0.55 | Based on $0.12-$0.19 per kWh |
| Propane per 10,000 BTU input per hour | $0.16 | $0.25 | $0.35 | Based on $1.50-$3.20 per gallon |
| 20,000-BTU natural gas appliance, 1 hour daily | $1.80/month | $3.00/month | $4.80/month | 30 hours of full-rate operation |
| 40,000-BTU electric heater, 5 hours daily | $63/month | $75.60/month | $99/month | 150 hours at full draw |
Assumptions: Fuel prices are illustrative U.S. ranges; fixed utility fees and taxes are excluded. One therm equals 100,000 BTU, and one kWh equals about 3,412 BTU.
Hourly BTU fuel costs for common appliances
Hourly operating cost is the price of the energy consumed during one hour at the stated firing rate. For gas, divide the appliance’s BTU input per hour by 100,000 to find therms used per hour, then multiply by the price per therm. For electric resistance heat, divide BTU per hour by 3,412 to estimate kilowatts, then multiply by the electricity price per kilowatt-hour.
At the same 10,000-BTU rating, electric resistance heat usually costs more per hour than natural gas at typical residential rates. The comparison changes with local prices and equipment efficiency, so a local bill or supplier quote makes the estimate more useful.
| Appliance or rating | Fuel and rate assumption | Estimated hourly cost | Typical use |
|---|---|---|---|
| 10,000 BTU | Natural gas, $1.00/therm | $0.10 | Small burner or low furnace stage |
| 30,000 BTU | Natural gas, $1.00/therm | $0.30 | Gas fireplace or patio heater |
| 40,000 BTU | Propane, $2.50/gallon | $1.09 | Propane heater at rated input |
| 10,000 BTU | Electricity, $0.15/kWh | $0.44 | Resistance heater equivalent |
Assumptions: Gas and propane figures use fuel input ratings, not delivered heat. Electric cost assumes resistance heating and excludes demand charges.
How the BTU-to-dollar calculator formula works
For natural gas, use this formula: BTU per hour ÷ 100,000 × price per therm. If a furnace input is 60,000 BTU per hour and gas costs $1.20 per therm, full-rate fuel cost is 0.6 × $1.20, or $0.72 per hour. The utility’s price per therm may include delivery charges, so the bill’s effective rate can differ from a supplier’s advertised commodity rate.
For electricity, calculate BTU per hour ÷ 3,412 × price per kWh. A 10,000-BTU-per-hour resistance heater at $0.16 per kWh uses about 2.93 kWh, costing roughly $0.47 per hour. For propane, divide BTU per hour by about 91,500 BTU per gallon, then multiply by the delivered gallon price. Propane heat content varies slightly by source and blend.
Use the appliance’s input rating for fuel consumed, and account for efficiency when estimating useful heat output. If a heater delivers 10,000 BTU of heat at 80% efficiency, it needs 12,500 BTU of fuel input to deliver that amount. Conversely, if its label lists 10,000 BTU input, its useful output at 80% efficiency is about 8,000 BTU.
Calculator formula: natural gas hourly cost = BTU_input_per_hour ÷ 100,000 × dollars_per_therm. Electric hourly cost = BTU_per_hour ÷ 3,412 × dollars_per_kWh.
Utility rates and fuel units that change the result
Residential energy prices vary by state, utility territory, season, and contract. A reasonable planning range is $0.12-$0.19 per kWh for electricity and $0.60-$1.60 per therm for natural gas, though some locations fall outside those bands. Delivered propane commonly ranges from $1.50-$3.20 per gallon, with rural delivery, tank rental, minimum fills, and winter demand affecting the invoice.
Check the latest bill for the total variable energy charge, not only a headline rate. Gas bills may show a price per therm or per hundred cubic feet; electricity bills show cents per kWh. If gas is billed per CCF, the utility’s conversion factor can vary, but a typical CCF contains roughly 100,000 BTU. Fixed monthly service charges should not be counted as hourly fuel cost unless calculating the full bill impact.
Use the rate that applies to the next unit of energy, including variable delivery charges where shown. Tiered tariffs, time-of-use pricing, and seasonal adjustments can make a single annual average inaccurate for a heater used mostly on cold evenings.
Efficiency ratings and BTU input versus heat output
Efficiency matters when comparing the cost of delivering a set amount of heat. A 90% efficient furnace turns about 90% of its fuel energy into useful heat under rated conditions; a 70% efficient unit needs more fuel to deliver the same output. To estimate the cost of one hour at a target heat output, divide that output by the efficiency before applying the fuel-cost formula.
For example, delivering 30,000 BTU of useful heat with an 80% efficient gas heater requires 37,500 BTU of fuel input. At $1.20 per therm, that is about $0.45 for the hour. A label that already states input capacity should not be adjusted a second time unless the calculation is explicitly about delivered heat.
Efficiency adjustments belong in the calculation only when the BTU figure represents useful output rather than fuel input. Heat pumps need separate treatment: their rated heating output is not equivalent to electric resistance consumption, because they can deliver multiple units of heat per unit of electricity. Use the unit’s power draw or coefficient-of-performance data for a more accurate heat-pump estimate.
What 10,000 to 80,000 BTU ratings cost per hour
The table shows how capacity scales hourly expense under sample rates. These are full-output estimates, not guaranteed bills: thermostats, burners, cycling, wind, insulation, and outdoor temperature affect actual consumption. A furnace rated at 80,000 BTU input will not necessarily burn at that rate for every hour the thermostat is on.
| BTU input per hour | Natural gas at $1.00/therm | Propane at $2.50/gallon | Electric resistance at $0.15/kWh |
|---|---|---|---|
| 10,000 | $0.10/hour | $0.27/hour | $0.44/hour |
| 20,000 | $0.20/hour | $0.55/hour | $0.88/hour |
| 40,000 | $0.40/hour | $1.09/hour | $1.76/hour |
| 80,000 | $0.80/hour | $2.19/hour | $3.52/hour |
Assumptions: Natural gas contains 100,000 BTU per therm, propane contains 91,500 BTU per gallon, and electricity converts at 3,412 BTU per kWh. The table excludes efficiency losses and fixed fees.
Runtime, cycling, and monthly heater expense
Convert hourly cost to a monthly estimate by multiplying by full-rate hours per day and operating days in the month. A 30,000-BTU gas appliance costing $0.30 per full-output hour, used at that rate for three hours daily over 30 days, would cost about $27. If it runs at full input only half the time, the fuel estimate is closer to $13.50.
Thermostat “on” time is not always burner runtime. A furnace may cycle on and off, and a modulating model may operate below its maximum input. For a rough estimate, record actual burner or element run time, or apply a duty-cycle estimate: hourly full-load cost × operating hours × fraction of time at full load.
Monthly cost estimates improve when they use actual fuel-running hours rather than total hours in the day. A portable heater used eight hours daily can have a very different bill from a furnace that cycles intermittently across the same period.
Three real-world hourly cost examples
A 30,000-BTU gas fireplace at $1.10 per therm costs about $0.33 per full-output hour. If it runs at full rate for four hours each evening, the estimate is $1.32 a day or roughly $40 over 30 days. This excludes any fixed gas account fee already being paid for other appliances.
A 40,000-BTU propane patio heater at $2.75 per gallon uses about 0.437 gallon per hour, costing around $1.20 per full-output hour. Three hours of use on 12 evenings would total about $43. A tank exchange price may imply a higher per-gallon rate than a bulk delivery contract.
A 10,000-BTU electric resistance heater at $0.18 per kWh draws about 2.93 kWh per hour and costs approximately $0.53 per hour. Used for six hours daily for 30 days, it would add about $95 to the variable electricity charge. A thermostat or lower setting may reduce runtime, but the hourly rate at full draw remains similar.
These examples show why fuel type, local rate, and actual hours matter as much as the BTU rating. They are estimates for full-output operation and should not be treated as quotes for a complete utility bill.
Reduce BTU operating cost without misreading capacity
First, check whether the appliance’s label gives input or output BTU. Compare equipment using the same basis, and use the bill’s effective variable fuel rate. Correct sizing also matters: an oversized heater can cycle frequently, while an undersized unit may run continuously without meeting the heating load.
For space heating, sealing drafts, improving insulation, and lowering the thermostat can reduce the hours of operation. Clean filters and unobstructed vents help forced-air systems move heat as designed. For portable heaters, heating an occupied room instead of an entire home may reduce total energy use, provided the equipment is used according to its safety instructions.
Reducing heat loss and runtime often saves more than refining a rough hourly estimate. Compare a repair or maintenance expense with the expected fuel savings before replacing a working appliance, and include installation cost and efficiency assumptions when comparing models.