How to Size a Pool Heater (Complete Guide)

Pool Heater Sizing Formula

BTU needed = Pool Gallons × 8.34 × Temperature Rise ÷ Desired Heatup Time (hours) ÷ Heater Efficiency

Most residential pool heaters are 80% efficient. Common sizes: 200K, 266K, 300K, 400K BTU.

Factors That Affect Sizing

• Pool volume: More water = more BTUs needed
• Temperature rise: Difference between current and desired temp
• Wind exposure: Wind dramatically increases heat loss
• Pool cover: A cover can reduce heat loss by 50-70%
• Climate: Colder climates need bigger heaters

Heater Types Compared

Gas Heaters (Natural Gas/Propane)

• Fastest heating (1-2°F per hour for typical pool)
• Works in any weather
• Higher operating cost ($200-$600/month)
• Best for: occasional use, spas, quick heatup

Heat Pumps

• Slower heating (1-2°F per hour in warm weather)
• Very efficient (COP 5-6, 500-600% efficient)
• Low operating cost ($50-$150/month)
• Doesn't work well below 50°F ambient
• Best for: regular use in mild climates

Solar Heaters

• Free operating cost (just pump electricity)
• Requires roof space for panels
• Only works during sunny hours
• Can extend season 2-3 months
• Best for: supplemental heating, warm climates

Use our heater sizing calculator to find the right BTU rating.