Pool Heater Size Calculator

The right pool heater size depends on pool volume, desired temperature rise, and how quickly you want to heat up. The standard formula is BTU/h = (gallons × 8.34 × temperature rise °F) ÷ heating hours, with a 25% buffer for ongoing heat loss. As a rule of thumb, a typical 15×30 ft pool (~17,000 gallons) heated 15°F over 24 hours needs roughly 60,000–72,000 BTU/h. Use the pool heater size calculator above for your exact pool, then browse our Apollo air-to-water lineup to match your result to a unit.

Initial heat-up takes 24–72 hours depending on pool size, temperature rise, and heat pump capacity. The heat-up time table in the calculator above shows the exact estimate for your pool across all three Apollo air-to-water sizes. Once at target temperature, maintaining it uses far less energy — the heat pump only compensates for daily losses from evaporation, wind, and radiation. Contact us if you need help choosing the right capacity for your heat-up timeline.

Yes, significantly. A pool cover reduces evaporative heat loss — which accounts for up to 70% of total pool heat loss — by around 30% on average. Toggle the pool cover option in the calculator above to see exactly how much it shifts your BTU requirement. A cover can mean the difference between needing a 5T or 6T unit. See BTU specs across our Apollo lineup once you have your adjusted number.

COP (Coefficient of Performance) measures heat delivered per unit of electricity consumed. A COP of 4.0 means 4 kWh of heat for every 1 kWh of electricity. The Apollo air-to-water series typically achieves COP 3.5–5.0 for pool heating, making running costs significantly lower than gas or electric resistance heaters. See COP and BTU specs across our full Apollo air-to-water lineup to compare running costs by unit size.

Standard heat pumps lose efficiency below 10°C (50°F) and stop below 5°C. The Apollo EVI series maintains reliable output down to 14°F (−10°C), extending your pool season into early spring and late fall at a fraction of gas heating costs.

Yes. Air-to-water units heat a closed hydronic loop and do not connect to open pool plumbing directly. A titanium or cupro-nickel heat exchanger transfers heat to the pool water while protecting the unit from chlorine and bromine damage. Contact us for help selecting a compatible heat exchanger for your pool setup.

Running two Apollo 6T air-to-water units in parallel on a shared hydronic loop doubles output, scales cleanly, and halves heat-up time without oversizing a single unit. Our team will design the right multi-unit system for your pool at no charge — call 1-888-301-0737 or use the Contact Us button above.