Pool Pump Selection Help

Because swimming pools are a popular household luxury throughout the world, many homeowners need to know how to select the right pool pump for their individual needs. Choosing the proper pool pump can reduce the energy cost of maintaining a pool. Differences in design will affect cost and efficiency. Always research different brands and types of pool pumps to ensure the best model is selected for the pool.

Selecting a Pool Pump

When your pool was built your pool builder would have correctly sized the pump for your pool. If no equipment has been changed since pool was built the pump will be the right size. Unfortunately this is not always the case so you will need to check what size pool pump you have and compare it to what size would generally be used for that pool.

Most people think you select your poor pump size according to how much water is in the pool but this is not the full story.

You actually need to size your pump to the filter that is being used in the pool and this is far more important for the following reasons:

A pump that is too large for a sand filter will not filter properly, the water passes across the sand with too much velocity and actually creates vertical channels in the sand bed, the high-speed water passes down these channels and does not get filtered by the sand.
A pump that is too large for a sand filter will also cause there to be too much pressure on the tank of the sand filter this can cause premature failure of the tank and laterals, the extra backpressure will also cause premature failure of the pump.
A pump that is too small for a sand filter will not backwash properly meaning the sand will not be lifted and cleaned once a month as it should be. The sand then becomes partially blocked and the system runs under too much pressure causing problems.
A pump that is too small for a sand filter can also result in a pool with low water turnover and dead zones in the pool which is often observed as algae in the corners or steps, if the pool has a salt chlorinator cell may not fill with water and the chlorinator will then turn automatically off and stop making chlorine.
Similarly cartridge filters will be under too much pressure if the pump is too large and the tank will fail prematurely. The cartridge element itself will also fail prematurely.
A pump that is too small for a cartridge filter is not as big an issue except for insufficient turnover of pool water and if it is a saltwater pool this cell may not filled with water properly and stop producing chlorine.
How to size the pump.

The first step is to look at the label on your existing pump, look at how many kilowatts the pump is rated for

around 0.75 kilowatts means it's a 1 horsepower pump
around 1.10 kilowatts means it's 1.5 horsepower pump
In domestic pools these are the two most common sizes.

Just for reference

around 0.5 kilowatts means it's 3/4 horsepower pump
around 1.7 kilowatts means it's 2 horsepower pump
Next look at the diameter of your sand filter there are a few common sizes:

around 20 inches
around 25 inches
around 28 inches
around 31 inches
If you have a cartridge filter these will be either 50, 100, 150, 200 square foot you can find this out from the label on your filter or measure is physical dimensions and compare it to other filters to get cartridge rating in square feet.

Which pump for which filter and pool

3/4 Horsepower pump works best with a 20 inch sand filter or a 75 sq ft cartridge filter and a pool size of less than 28 000 litres
1.0 Horsepower pump works best with a 25 inch sand filter or a 100 sq ft cartridge filter and a pool size of less than 55 000 litres although it can be used on larger pools.
1.5 Horsepower pump works best with a 28 inch sand filter or a 150 sq ft cartridge filter and a pool size of less than 110,000 litres
2.0 Horsepower pump works best with a 31 inch sand filter or a 250 sq ft cartridge filter and a pool size over 110,000 litres

Operating Costs

Owners should always take into consideration that the least powerful pump that will suit the needs of the pool will save on energy costs. Operating the pool pump for only eight hours a day will greatly reduce energy costs. Ultimately, selecting a pool pump will not depend on how much it costs initially but rather how much it costs to maintain the pool utilizing that pump.