Estimate monthly costs to heat your pool. Compare gas, electric heat pump, and solar heating options based on your climate and target temperature. Accurate cost modeling helps you choose the most economical heating technology for your specific backyard setup.
Heating cost depends on how much energy it takes to raise your water and what that energy costs, so gather a few inputs. Enter pool volume in gallons or liters, your current water temperature, and your target temperature, the difference (the temperature rise) drives everything. Select your heater type: gas (rated in BTU/hr and burning therms of natural gas or gallons of propane), an electric heat-pump (rated by a COP, coefficient of performance, around 5-6 in mild weather), or solar. Enter your local energy price: dollars per therm for gas or dollars per kWh for electricity. For ongoing costs, also note whether you use a solar cover, since most heat escapes by surface evaporation. Climate matters too: a cool, windy, exposed pool loses heat far faster than a sheltered warm-climate one, so an estimate is for the initial heat-up plus a daily maintenance figure, not a fixed monthly bill.
Core formula: energy to heat water = volume (lb of water) x temperature rise (deg F) x 1 BTU/lb-degF. Water weighs about 8.34 lb/gal. Worked example: heating 20,000 gallons (75,700 L) by 10 deg F (5.6 deg C) needs 20000 x 8.34 x 10 = 1,668,000 BTU. A gas heater is roughly 82% efficient, so fuel input = 1,668,000 / 0.82 = 2,034,000 BTU. One therm = 100,000 BTU, so that is about 20.3 therms; at $1.50/therm = about $30 to heat up (ignoring losses). With a heat-pump instead, 1,668,000 BTU = 489 kWh of heat; at a COP of 5 you draw 489 / 5 = 98 kWh, and at $0.18/kWh that is about $18. In metric: raising 75,700 L by 5.6 deg C is about 489 kWh of delivered heat, the same energy, just priced by your fuel and equipment efficiency.
Accurate estimates keep heating from quietly becoming your biggest pool expense, and the dominant variable is heat loss, not heat-up. Up to 70-80% of loss is evaporative from the surface, so the single highest-return move is a solar or liquid cover, which can cut heating energy by half or more; modeling cost without accounting for a cover badly overstates a heat-pump's advantage or understates an uncovered pool's bills. Common mistakes: ignoring efficiency (gas heaters are ~80-85%, never 100%), assuming a heat-pump's COP holds in cold air (it drops sharply below about 50 deg F / 10 deg C, where gas wins), and forgetting wind and night-time losses. Set a realistic target, every extra degree of water temperature costs noticeably more, and consider lowering the thermostat or covering the pool when it is unused for several days. Re-estimate seasonally as ambient temperatures and energy prices change, and verify with one real billing cycle to calibrate your local loss rate.
Heat pumps are significantly cheaper to run in moderate-to-warm weather. Gas heaters are more expensive but can heat a pool much faster and work in any temperature.
Most heat loss (70-80%) occurs through evaporation at the surface. Using a solar cover at night is the single most effective way to reduce your heating bills.
Yes. A solar cover acts as a thermal blanket, trapping heat and preventing evaporation. It can raise a pool's temperature by 5-10 degrees just from sun exposure alone.