Estimate one-time pool warm-up cost and monthly heater, pump, and pool-light costs from your pool size, equipment ratings, and utility prices.
Advanced options
Table of contents
How to use our Pool Heater Running Cost Calculator
- Choose Heater type, then enter the heater's active daily run time and rating from its label or documentation.
- Enter pool length, width, average water depth, current water temperature, and target water temperature for the warm-up estimate.
- Enter the applicable utility price. Electric heaters and heat pumps use Electricity price; natural gas and propane heaters use Fuel price.
- Open Advanced options to add pump and pool-light use, then set the billing-month days and the months you expect to heat the pool.
- Check that the separate heater, pump, and pool-light monthly costs add up to the Combined monthly pool running cost. Compare the first-month total with later months to see the one-time warm-up effect.
Definitions
Active heater run time: Hours per day when the heater is actually operating. It can be less than pump run time.
Heater rating: Electrical draw in kW for an electric resistance heater or heat pump, or heat output in Btu per hour for a natural gas or propane heater.
COP: Coefficient of performance. For a heat pump, it is heat delivered to the pool divided by electricity used; a COP of 4 means 4 units of heat moved for each unit of electric energy used. [1]
Heater efficiency: The share of fuel energy that becomes useful heat. Gas and propane calculations use this percentage.
Therm: A natural-gas energy unit equal to 100,000 Btu.
Initial warm-up: Raising the pool from Water temperature now to Target water temperature once, before regular daily running costs.
Common mistakes and quick fixes
Mistake: Entering a gas heater's Btu per hour rating as if it were kW in Heater rating.
Fix: For natural gas or propane, enter heat output in Btu per hour. For electric resistance and heat pumps, enter electrical draw in kW.
Mistake: Using total pump-on time as Heater run time.
Fix: Enter only the average hours when the heater is actively running. Enter separate circulation time in Pump run time.
Mistake: Entering pool wall depth instead of Average water depth.
Fix: For a sloped pool, use the average of the shallow and deep water depths.
Mistake: Leaving an old utility charge in Fuel price after switching to an electric heater.
Fix: Use Electricity price for electric resistance and heat pumps. Use Fuel price only for natural gas or propane.
Mistake: Expecting Estimated one-time pool warm-up cost to include weather losses.
Fix: Treat it as the energy stored in the water for the entered temperature increase; real warm-up cost can be higher.
Mistake: Entering light wattage in kW for Pool light power.
Fix: Enter watts, such as 100 for a 100-watt light. The calculator converts watts to kW for the cost calculation.
Limitations & Key Assumptions / Boundary Conditions
- The pool volume estimate assumes a rectangular pool with a consistent average water depth. Use a measured gallon capacity for an irregular shape if available.
- The warm-up estimate counts heat stored in the water. It does not model air temperature, wind, humidity, evaporation, a pool cover, plumbing losses, or heat lost while warming.
- Heat-pump COP and gas or propane efficiency can change with equipment condition and operating conditions. Use your equipment documentation when possible.
- Monthly and seasonal totals assume the same daily run times and utility prices for every selected billing period.
- Pump and pool-light costs are included only when their electrical draw and daily use are entered. Other equipment, such as a salt system or cleaner, is not included.
- Utility bills may include fixed charges, taxes, demand charges, or tiered prices that are not included in the entered energy price.
Methodology
Calculation method
The calculator first estimates water volume from the entered rectangular dimensions. It then estimates the heat needed to raise that water to the target temperature. Monthly equipment costs use the entered active run times and utility prices.
gallons = length_ft * width_ft * average_depth_ft * 7.48052
heat_btu = gallons * 8.34 * max(0, target_temp_f - current_temp_f)
For electric resistance heating, warm-up electricity is heat needed divided by 3,412.142 Btu per kWh. For a heat pump, that amount is also divided by COP. For natural gas and propane, the heat needed is divided by heater efficiency and the fuel energy per therm or gallon.
electric_warmup_cost = heat_btu / (3412.142 * COP) * electricity_price
fuel_warmup_cost = heat_btu / (efficiency * fuel_btu_per_unit) * fuel_price
For electric resistance and heat pumps, monthly heater cost uses electrical draw in kW. For natural gas and propane, it uses the entered Btu-per-hour heat output, efficiency, and fuel price.
pump_monthly = pump_kw * pump_hours_day * electricity_price * days_per_month
lighting_monthly = (light_watts / 1000) * light_hours_day * electricity_price * days_per_month
combined_monthly = heater_monthly + pump_monthly + lighting_monthly
season_cost = warmup_cost + combined_monthly * season_months
Worked example
A 20 by 10 foot pool with a 4 foot average depth holds about 5,984 gallons. Raising it from 75 F to 80 F with a 4 kW resistance heater at $0.15 per kWh costs about $10.97 for the water-only warm-up. Running that heater 4 active hours per day for 30 days costs $72.00, so the first-month total is about $82.97 before any pump or pool-light cost.