Pool Pump Electricity Cost Calculator

How it works

A pump's cost is its electrical input power times the hours it runs times your rate. A motor's horsepower is its shaft output, so the electricity it draws is the horsepower in watts (745.7 W per hp) divided by the motor's efficiency. If you have a nameplate instead, input power is volts × amps × power factor; if you have measured watts, enter them directly.

Centrifugal pumps follow the affinity laws: flow is proportional to speed and power to the cube of speed. Halving the speed halves the flow, so filtering the same water takes twice as long, but the pump draws only one-eighth the power. The energy for the same water is the speed squared: one-quarter at half speed.

The comparison applies those laws to the same pump at the reduced speed you enter. If moving the same water at that speed would take more than 24 hours a day, the reduced-speed results read "Not possible within 24 h" and the full-speed costs are still shown. A monthly figure uses an average month of 30.44 days; the season figure uses the days you enter.

Formula

input W (hp)        = hp × 745.7 ÷ motor efficiency
input W (nameplate) = volts × amps × power factor
kWh per day         = input W × hours ÷ 1,000
cost per day        = kWh per day × rate ÷ 100
cost per month      = cost per day × 30.44;   cost per season = cost per day × days
reduced speed s:  hours = hours ÷ s;  W = input W × s³;  kWh per day = kWh × s²
season savings      = season cost × (1 − s²)

Example

A 1.5 hp motor at 75 % efficiency draws 1.5 × 745.7 ÷ 0.75 = 1,491 W. Running 8 hours a day it uses 11.93 kWh, which at 18 ¢ per kWh is $2.15 a day, $65.37 a month and $386.57 over a 180-day season.

At 50 % speed the same water takes 16 hours a day at 186 W, 2.98 kWh a day: $96.64 a season, $289.93 less.

Assumptions and limitations

• The affinity laws are ideal. Real pool systems have static head, filter and heater pressure drops, and drive and motor losses that change with speed, so variable-speed savings at very low speeds are smaller than the cube law predicts. ENERGY STAR states the ideal case: "reducing pump speed by one-half allows the pump to use just one-eighth as much energy", meaning per hour of running, which is power.
• Horsepower is converted with the mechanical horsepower of 745.7 W (the 746 W often quoted is the rounded electrical horsepower); the motor efficiency default is a typical value. A pump's actual draw depends on how heavily it is loaded, so a measured wattage is more reliable than horsepower or nameplate amps.
• Run hours, rate and season length are held constant; the 18 ¢ rate default is illustrative. Tiered and time-of-use tariffs are not modelled.
• Whether the reduced flow still meets the pool's filtration, chlorination, heater and skimmer requirements is not checked; those depend on the equipment manufacturer's instructions and local health or building codes.

Frequently asked questions