Click Here to Download Pool Tip #51: Pool Heater Sizing (PDF format, 36KB)

Pool Heater Sizing for Temperature Maintenance

• Find pool surface area (ft²)
• Multiplied by 15 –– a constant that represents the BTUs required to raise water temperature one degree per square foot of surface area, then
• Multiply by the desired increase in water temperature over ambient air temperature (maximum temperature rise)
• This will give you the heater output
• After obtaining the required heater output, divide the heater efficiency rating (Ex. ÷ .82) to determine the heater input needed (I = O ÷ E / O = I × E)

Example:
Surface area: 75′ × 48′ = 3,600 square feet
Desired temperature: 85°:
Max. temperature rise: 35°:
Heater efficiency rating: 82%
Heater output: 3,600 × 15 = 54,000 × 35°: = 1,890,000 BTUs
Required heater input: 1,890,000 ÷ .82 = 2,304,878 BTUs

Pool Heaters – Time Needed to Heat Pool Water

• Determine the number of BTUs needed to raise _____ gallons of pool water from ___°: F to ___°: F.
• Use the formula 1 BTU will raise 1 pound of water 1°: F in 1 hour
• Multiply the volume in gallons by 8.33 (weight of 1 gallon of water) to determine the weight of the water that must be heated.
• Multiply the water weight by the desired temperature rise to determine the number of BTUs needed.
• Divide the BTUs needed by the available heater output in BTUs to find the number of hours it will take to heat the water.

Example:
Water volume: 165,000 gallons
Temperature rise: 35° F
Water weight: 165,000 gallons × 8.33 = 1,374,450 lbs
1,374,450 lbs × 35°: F = 48,105,750 BTUs needed to heat
Heater output: 1,890,000 BTUs
48,105,750 BTUs needed to heat to desired temperature ÷ 1,890,000 BTUs output = 25.4 hours