What you really need to know about the two-speed pool pumps
The two-speed pumps will typically operate much like a single speed pump, but with the option of also running on a “low” speed. This differentiation is made using a toggle switch or electronic control method of some sort. This kind of pumps will operate at 3,450 RPMs when on high, and 1,725 RPMs on low. In most cases, the low setting is used for basic circulation and filtration functions, and the high setting will be reserved for activities that require more power, such as vacuuming a pool or when running your pool heater (heaters may require higher flow rates). Figure a GPM (gallons per minute) of 10 per 100k BTU. So a 300k BTU heater will require at least a 30 GPM flow rate.
Having a two-speed pump is advantageous because it provides more versatility than a single speed pump. The pump is primarily needed to circulate and filter the water in your pool, so you can use the low speed 70 to 80% of the time, this will save energy and provide a much quieter operation. On the other hand, if you require greater suction or water movement, a two-speed pump can be turned to high, providing the same power as a single speed pump.
Although many people are beginning to make the switch to two-speed pool pumps, bringing the prices down, the cost to purchase a two-speed unit is still higher than that of a single speed pump ($550.00 in ground / 350.00 above ground). Another disadvantage is it will not save you as much money as a variable speed pump could. With special incentives from electric companies, and mail in rebate offers from manufacturers, a variable speed pump may actually cost less up front.
The low speed is actually too low to run most heaters. It also offers to little flow for above ground pools. The usually require the operator to manually switch the speed, so it usually gets left on just one speed
One last negative: Two speed pumps actually use to separate copper windings in the motor to operate the two speeds. So these pumps will be as noisy as single speed pumps.
Two-speed pumps come in just about as many brand choices as single speed pumps, with some of the most popular ones being Hayward, Reliant, and Pentair.
With the cost of variable speed pumps coming down and the introduction in 2015 of a 1.5 hp variable speed pump that runs on 110 voltage, 2-speed pumps don’t look as attractive.