Calculate how long it takes to heat your pool to the desired temperature based on heater BTU output and pool volume.
Don't know? Use our Pool Volume Calculator
Check your heater's nameplate or specs
Gas: 80-95%, Heat pump: 300-600% (COP)
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This is the theoretical minimum time. Actual time may be longer due to heat loss from evaporation, wind, and ambient temperature.
Planning a pool party or just want to know when your pool will be warm enough to swim? This calculator estimates how long your pool heater needs to run to reach your desired temperature.
The time to heat a pool is calculated using:
Time (hours) = (Pool Gallons × 8.33 × Temperature Rise) ÷ Heater BTU/hr
Where 8.33 is the weight of water in pounds per gallon.
For example, a 30,000-gallon pool heated from 65°F to 85°F (20°F rise) with a 400,000 BTU/hr heater: (30,000 × 8.33 × 20) ÷ 400,000 = 12.5 hours
Larger pools contain more water and require more BTUs to heat. Heating time increases proportionally with volume.
A larger temperature rise requires more time. Heating from 70°F to 80°F takes half as long as heating from 60°F to 80°F.
Higher BTU heaters heat faster but cost more to operate. Common residential sizes are 200,000-400,000 BTU.
This calculator shows theoretical minimum time. Real-world heating takes longer due to:
For a 20,000-gallon pool with a 400,000 BTU heater, heating 10°F takes approximately 4-5 hours. Larger pools or smaller heaters take proportionally longer.
It's usually more efficient to heat during the day when ambient temperatures help. Use a pool cover at night to retain heat. Continuous heating is fine but costs more in fuel.
The calculation assumes no heat loss. In reality, heat escapes through evaporation, radiation, and convection. Using a solar cover can make actual times closer to calculated times.
Bigger heaters heat faster but cost more upfront and to operate. Right-size your heater based on how quickly you need to heat and how often you'll use it.
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