Pool Heat Pump Size Calculator
Estimate the BTU/hr capacity you need to heat your swimming pool — using dimensions or gallons, a target temperature rise, and your desired heat-up time. Optional cover and wind settings add a practical loss margin.
On this page: Calculator · How it works · FAQ
Calculator
This calculator provides a planning estimate. Real-world performance depends on climate, evaporation, cover usage, plumbing/flow, and heat pump rating conditions. Use the recommended tier as a starting point, then validate with your equipment specs and installer guidance.
Shop pool heat pumps
Once you know your required BTU/hr tier, look for a unit rated at or above that output at your expected outdoor temperature. Most pool heat pumps are rated at 80°F air / 80°F water — performance drops in cooler conditions, so add 10–20% margin if your season starts early or runs late.
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Estimate monthly electricity cost with the energy cost calculator. For general heat pump sizing, see the heat pump calculator.
How the pool heater sizing works
The heat-up estimate is based on the energy required to raise pool water temperature: BTUs ≈ gallons × 8.34 × °F rise, divided by your chosen number of hours. We then add a practical margin for heat loss depending on cover usage and wind exposure.
Common size tiers
Pool heat pumps and heaters are commonly marketed in BTU/hr “classes” (for example 70k, 90k, 110k, 140k). The recommended tier helps you choose a product class that matches your goal.
Related: Electricity cost calculator · BTU calculator for rooms · Heat pump sizing (home)
Frequently asked questions
What does BTU/hr mean for a pool heater or heat pump?
BTU/hr is the heater's output rate — how many British Thermal Units it can deliver per hour. Higher BTU/hr means faster heat-up and better ability to maintain temperature in windy or uncovered conditions. A 100,000 BTU/hr pool heat pump heats roughly twice as fast as a 50,000 BTU/hr unit for the same pool size.
How do you estimate BTU/hr to heat a pool?
The standard approach: BTUs needed = gallons × 8.34 × °F rise. Divide by your desired heat-up hours to get required BTU/hr. Then add a margin for heat loss from wind and evaporation — typically 10–30% depending on cover usage and wind exposure. The calculator above does this automatically.
Does a pool cover reduce required heater size?
Yes, significantly. Covers reduce evaporation-driven heat loss, which is the largest source of pool heat loss. A covered pool can maintain temperature with a smaller heater than an uncovered pool in the same conditions. If the pool is covered when not in use, you can often size closer to the heat-up requirement rather than adding a large loss margin.
What BTU/hr pool heater size do I need?
Start with the heat-up requirement (gallons × 8.34 × desired °F rise ÷ hours). Then add margin for heat loss. Windy, uncovered pools typically need more BTU/hr to reach the same temperature in the same time. Use the calculator above with your pool dimensions and conditions for a recommended size tier.
Do heat pumps heat slower than gas heaters?
Many pool heat pumps provide lower BTU/hr than large gas heaters, but are more efficient in mild-to-warm climates where the ambient air temperature is above 50–55°F. For early-season or late-season heating in cooler climates, a gas heater may heat up faster. The BTU/hr output target from the calculator applies to both heater types.
Should I oversize a pool heat pump?
Modest oversizing (10–20%) can shorten heat-up time and improve performance in windier conditions. If you use a cover consistently and your pool is sheltered, you can often size closer to the calculated heat-up target. Oversizing significantly increases upfront cost without proportional benefit for covered, sheltered pools.