Heating & BTU Sizing
Pool Heater BTU & Sizing Calculator
Calculate the exact BTU rating needed for gas heaters and electric heat pumps based on pool surface area, volume, and target temperature rise.
Pool Heating Sizing Engine
Compute BTU output needed for pool heaters
20,000 gal
+15°F Rise
E.g., raising 70°F water to 85°F = 15°F Rise
10 Hours
Required BTU Rating+15°F in 10h
Minimum Required BTU Output
250,000 BTUs
(Calculated Exact: 249,900 BTUs/hr)
Recommended Equipment Match:250,000 - 266,000 BTU Heater
Recommended Pool Heaters
Explore top-rated Hayward Universal H-Series and Pentair MasterTemp gas pool heaters.
Check Pool Heater Prices on AmazonHeat Loss Pro Tip:
Using a solar cover traps up to 75% of water heat overnight, allowing you to use a smaller BTU heater.
BTU Calculation Formula
BTUs Required = Pool Volume (Gallons) × 8.33 × Desired Temp Rise (°F) ÷ Target Heating Time (Hours)
20,000 Gallons × 8.33 × 15°F Rise ÷ 10 Hours = ~250,000 BTUs RequiredRelated Equipment Tools
Frequently Asked Questions About Pool Heater BTU Sizing
Learn how to choose between Natural Gas, Propane, and Electric Heat Pumps.
A rule of thumb for gas pool heaters is 1,000 BTUs per 100 to 150 gallons of pool water, or approximately 8.33 BTUs per gallon per degree Fahrenheit of desired temperature rise.
Gas heaters heat pools very quickly in any weather, making them ideal for spas or weekend use. Heat pumps are much more energy-efficient for maintaining steady 80°F–85°F water throughout the entire pool season in warmer climates.
A properly sized 400,000 BTU gas heater takes approximately 4 to 6 hours to raise a 20,000-gallon pool by 10°F. A 120,000 BTU heat pump takes 12 to 18 hours.
Yes! A solar thermal blanket traps up to 75% of heat that would otherwise be lost to night evaporation, effectively reducing heater sizing requirements and fuel costs by up to 50%.