A swimming pool pump supplies the power to move pool water toward the filter so that it can be cleaned on a regular basis. When the entire volume of water in the pool runs through the filtration system one time, the pump has completed a “turnover.” An effective pump will turn over or circulate the water at least once every 12 hours.
Local regulations often stipulate a minimum turnover time, so check with your building department. Many people prefer to exceed regulations and opt for a turnover rate of 10 or 8 hours. The more water in the pool and the faster the turnover rate, the bigger the pump needed. Pumps are sold with a “gallons per minute” or GPM rating.
The pump works together with a system of pipes that drain the pool. The whole system works best when the hydraulic equation for the pipe diameter, length, and pump motor are properly sized to handle the volume of water that needs to turn over in the course of 12 hours (or whatever your preferred turnover rate is).
The pump supplier will have charts with specific recommendations. Generally, you can improve the efficiency of your pump by using shorter lengths of pipe, that is, by keeping the pump close to the pool, by avoiding 90-degree angles, by increasing the size of your pool’s filter, and by regularly clearing out the pool grates.
To calculate the gallons per minute that your pump needs to circulate, multiply your pool’s total volume in gallons times two; this will give you the gallons per day that the pump needs to circulate so that the water will turn over twice. (Multiply by three if you want the water to turn over every eight hours.)
Divide this number by 24 to get the gallons per hour, and divide again by 60 to get the gallons per minute. For instance, a pool that holds 10,000 gallons of water would need a pump that can handle 20,000 gallons per day for a 12-hour turnover rate. Dividing 20,000 by 24 would give the gallons per hour, and then dividing that by 60 would give the gallons per minute: 20,000 divided by 24 = 833; 833 divided by 60 = 13.88 GPM.
Energy efficiency is increasingly a concern with pool-pumping systems. In California, a state with a lot of pools, there are laws limiting pump energy consumption. Ideally, you want a pump that is big enough to circulate the water at the turnover rate you need, but not one so big that it’s wasting energy.
The EPA recommends running a pump just three hours a day, and based on water quality, increasing pump time in half-hour increments as needed. In addition, it recommends scrubbing the pool walls and using chemical additives to offset the reduction in pump time.
Another energy-efficient recommendation is to buy a two-speed or variable-speed pump just large enough to circulate the water twice a day and run it 24 hours a day, seven days a week. Most motors cannot run 24/7, but a two-speed/variable-speed pump can be used around the clock. This option is more expensive initially, but it saves energy and money in the long run, and these motors are very quiet.
Proponents of this option say that keeping the pump off for a long stretch of time—most people keep their pumps off for 12 to 16 hours each day—lets algae and debris build up and contributes to pH imbalance, all of which requires the pump to work harder. A smaller pump that works all the time prevents problems from developing and keeps water cleaner.