How do you calculate pool heater energy cost?

Multiply the heating demand in kBTU by the fuel price per therm, by the therms-per-kBTU factor, and by an efficiency correction. For 1,668 kBTU at $1.85/therm, 0.01 therms/kBTU, and a 1.22 correction for 82% efficiency, the cost is $37.65.

Why include an efficiency correction?

No heater turns 100% of its fuel into pool heat. An 82%-efficient heater wastes 18% up the flue, so you divide 100 by 82 to get 1.22 and multiply the raw fuel cost by that factor. Skip it and you underestimate the bill by nearly a quarter.

How do I find the kBTU demand?

Multiply pool gallons by 8.34 (lb per gallon) by the desired temperature rise in F, then divide by 1,000. A 20,000-gallon pool needing a 10 F rise is 20,000 x 8.34 x 10 / 1,000 = 1,668 kBTU.

What is a good energy price to enter?

Use your current utility rate per therm for natural gas. Propane and electric heat pumps should be converted to a propane- or kWh-equivalent per-therm rate so the comparison is apples to apples.

Natural gas vs heat pump for pool heating?

Gas heats fast and costs per therm; heat pumps move roughly 4-5 units of heat per unit of electricity but heat slowly and lose efficiency in cold air. Run both through this calculator using equivalent rates to see which wins for your climate and reheat speed.

Does this include the cost to hold temperature?

No. This is the cost of the initial rise only. Holding temperature against evaporation and conduction is a separate ongoing cost; a pool cover is the cheapest way to cut it.

Pool, Spa & Water Treatment Chemistry calculator

Pool Heater Energy Cost Calculator

Pool Heater Energy Cost tells you what it actually costs in fuel to raise a body of water to a target temperature, accounting for both the gas price and the real-world efficiency of the heater. Commercial pool operators, service technicians, and facility managers use it to price seasonal openings, quote reheat after a cold snap, and decide whether a high-efficiency heater upgrade pays back. Because heating is usually the single largest energy line on a pool budget, a few cents per therm or a few efficiency points move the number meaningfully. Running this before the season starts keeps you from underquoting a reheat job.

What this calculator does

Estimate heater energy cost from BTU demand, heater efficiency, and energy price.
Use it before heating a pool or spa, comparing schedules, or quoting event warmups.
It computes the fuel cost of a single heating event by multiplying kBTU demand by the fuel price, the therms-per-kBTU factor, and an efficiency correction.

Formula used

Energy cost = heating demand in kBTU x energy price x therms per kBTU x efficiency correction

Inputs explained

Heating energy demand: Divide total BTU demand by 1,000. BTU demand = pool gallons x 8.34 x desired temperature rise. For 20,000 gal and a 10 F rise, enter 1,668.
Fuel price per therm: Use current natural gas, propane, or heat pump equivalent rate per therm.
Therms per kBTU conversion: Enter 0.01 for natural gas (100 kBTU per therm). For propane, use a propane-equivalent rate.
Heater efficiency correction: Enter 100 divided by heater efficiency percent. For 82% efficiency, enter 1.22.

How to use the result

Use it when quoting a reheat, budgeting a season opening, or comparing fuel sources and heater efficiencies for the same temperature rise.
It captures fuel input only; it ignores standby heat loss, evaporation, and wind, so an uncovered or windy pool will cost more than the raw calculation shows.

Current U.S. benchmarks

As of Apr 2026, industrial natural gas averages 4.9 per Mcf across the U.S. (EIA), roughly 0.47 per therm, down 7.7% from a year earlier.
Global copper trades at $13,552 per tonne (IMF via FRED, Jun 2026), up 37.8% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.

Common questions

How do you calculate pool heater energy cost? Multiply the heating demand in kBTU by the fuel price per therm, by the therms-per-kBTU factor, and by an efficiency correction. For 1,668 kBTU at $1.85/therm, 0.01 therms/kBTU, and a 1.22 correction for 82% efficiency, the cost is $37.65.
Why include an efficiency correction? No heater turns 100% of its fuel into pool heat. An 82%-efficient heater wastes 18% up the flue, so you divide 100 by 82 to get 1.22 and multiply the raw fuel cost by that factor. Skip it and you underestimate the bill by nearly a quarter.
How do I find the kBTU demand? Multiply pool gallons by 8.34 (lb per gallon) by the desired temperature rise in F, then divide by 1,000. A 20,000-gallon pool needing a 10 F rise is 20,000 x 8.34 x 10 / 1,000 = 1,668 kBTU.
What is a good energy price to enter? Use your current utility rate per therm for natural gas. Propane and electric heat pumps should be converted to a propane- or kWh-equivalent per-therm rate so the comparison is apples to apples.
Natural gas vs heat pump for pool heating? Gas heats fast and costs per therm; heat pumps move roughly 4-5 units of heat per unit of electricity but heat slowly and lose efficiency in cold air. Run both through this calculator using equivalent rates to see which wins for your climate and reheat speed.

Last reviewed 2026-05-12.