Pool Heater Size Calculator

Pool heaters are sized two ways and this page runs both. The exact figure is the heat the water itself needs, volume in gallons times 8.34 pounds times the temperature rise, divided by the hours you are willing to wait and by the heater efficiency; the manufacturers' rule of thumb is surface area times rise times twelve, which allows for the heat the pool is losing while it warms. Enter the volume, the surface area, the rise and a heat-up time and you get both, the larger of the two, and the smallest stock nameplate that covers it. A second action takes a heater you already have, in natural gas, propane, heat pump or resistance form, and returns the hours, the therms or kilowatt hours and the cost. Standing heat loss is deliberately not blended into the exact figure, because it depends on wind, humidity and whether the pool has a cover.

Calculator Type
Measurements In
The metric setting reads the pool in litres, the surface in square metres, the temperature rise in degrees Celsius and a heater rating in kilowatts, prices gas per kWh and LPG per litre, and returns every figure the same way. Efficiency, COP and hours are the same number in both systems.
In US gallons, or in litres if the measurement choice is metric. Length x width x average depth x 7.48 for a rectangle in feet, or length x width x average depth x 1000 for one in metres, or use the pool volume calculator.
In square feet, or in square metres if the measurement choice is metric. The area of the water seen from above. Length x width for a rectangle.
In degrees Fahrenheit, or in degrees Celsius if the measurement choice is metric. Target water temperature less the temperature the pool sits at on its own. 1 to 60 F, or 0.56 to 33.33 C.
Around 82 to 84 per cent for a standard gas heater and 90 to 96 for a condensing one. Leave it at 84 if you do not know.
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Measurements In
The metric setting reads the pool in litres, the surface in square metres, the temperature rise in degrees Celsius and a heater rating in kilowatts, prices gas per kWh and LPG per litre, and returns every figure the same way. Efficiency, COP and hours are the same number in both systems.
In US gallons, or in litres if the measurement choice is metric.
In degrees Fahrenheit, or in degrees Celsius if the measurement choice is metric.
In Btu/hr, or in kilowatts if the measurement choice is metric. For a gas heater this is the input rating on the nameplate. For a heat pump it is the output rating, which is how heat pumps are sold.
Coefficient of performance. Catalogue figures of 5 to 6 are measured at 80 F (27 C) air and 80 per cent humidity; the real one falls with the air temperature.
Dollars per therm for natural gas, per gallon for propane, per kilowatt hour for either electric option. On the metric setting it is dollars per kWh of gas, per litre of LPG, or per kWh of electricity.
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