Your swimming pool is a big investment, so you want it to run as smoothly and efficient for many years. Choosing the correct size swimming pool pump and pool filter system is imperative as these items are central to the running of the pool. By selecting the  most appropriate pump, it will ensure that your water is well-filtered and that the pipes and filter system won’t be damaged by excessive water pressure. It will also ensure that your pool is as energy-efficient as possible.

We do offer a very simple swimming pool sizing equipment guide that details which pump, filter, heater etc are suitable for certain size pools.

Although this chart is very useful and fairly accurate for most applications, there is mathematics behind these charts which we have included below. The information below can be used to calculate the correct size of swimming pool pump for your exact rectangle pool. If you have a shaped pool or would like some assistance in selecting the correct pump, please do not hesitate to contact us on 01895-672515

Measuring Your Pool

Step 1) Length, Width & Depth

Firstly measure your pool’s width, length and average depth. Write the measurements down in feet or meters, using decimals to approximate fractions of feet. (In other words, 20 feet, 3 inches would be 20.25 feet.)

Step 2) Calculate Pool Surface Area

Multiply the length of your pool by its width to determine its surface area.

Example: 10m x 5 = 50 m2   or   33ft x 16.5ft = 544.5 ft2

Step 3) Pool Surface Area x Pool Depth

Multiply the pool’s surface area by its depth.

Example: 50 m2 x 1.2m (depth) = 60  or   544.5 ft2 x 4 (depth) = 2178

Step 4) Calculate Pool Volume

If you have measured your pool in feet multiply the figure calculated in Step 3 by 6.25 to determine how many gallons of water your pool holds. This formula will work only if your pool is perfectly rectangular.  If you have measured your pool in meters, multiply the figure calculated in Step 3 by 1.0 to determine how many cubic meters of water your pool holds.

Example: 60 x 1.0 = 60 Cubic Meters  or  2178 x 6.25 = 13612.50 UK Gallons

Step 5) Convert UK Gallons to Cubic Meters

If you already have your pool volume in cubic meter then disregard this step.

As most swimming pool pump charts display cubic meters and not UK gallons you must do this conversion now. To convert UK gallons to cubic meters, divide the number of gallons you calculated in Step 4 by 220.

Example: 13612.50 Gallons divided by 220 = 61.88 Cubic Meters of Water

Choose a Swimming Pool Pump

Step 6) Approximate Pool Turnover Rate

A pool turnover rate is the amount of hours it takes to circulate the whole of your pool water through your swimming pool filter. Please select from the options below, the operation that relates to your swimming pool.

Outdoor Domestic Pool – Heavy Use – 4 Hours

Outdoor Domestic Pool – Light Use – 6 Hours

Indoor Domestic Pool – 8 Hours

Commercial Pool – 2.5 Hours

Hydrotherapy Pool – 1 Hours

Step 7) Minimum Flow Rate

Divide the number of cubic meters of water your pool holds (Step 4/5) by the number of hours you selected in Step 6.

For example if you have an indoor pool measuring 10m x 5m x 1.5m you would have calculated your pool to have 75 cubic meters of water (10 x 5 x 1.2 x 1.0m3).

60 cubic meters divided by 8 hours = 7.5 Cubic Meters / Per Hour

This figure will determine the minimum flow rate you need use to ensure the water in your pool can make a complete circulation.

Step 8 ) Pipework Maximum Flow Rate

Determine the maximum flow rate your pool can handle by looking at its plumbing system. Most domestic pools use 1.5 inch pipes, which can handle about 9 cubic meters per hour on the suction side and 15 cubic meters per hour on the return side.

A 2 inch pipe can handle more than this with about 15 cubic meters per hour on the suction side and 25 cubic meters per hour on the return side, while a 3-inch pipe can handle more than 34 cubic meters per hour.

Use a slightly lower flow rate if your plumbing has a lot of intricate turns and connections that could be stressed by too much rushing water.

Step 9) What is your Pool Filters Maximum Flow Rate?

You need to check at this point to make sure your filter’s maximum flow rate, specified by the manufacturer, will accommodate the size of your pump you are going to choose.

If you do not have a swimming pool filter you need to choose one of a larger size if you want the cleanest water with the lowest amount of maintenance. You will need to clean the filter when it becomes clogged with debris. A larger filter will take longer to clog.

Example: Your pool has a minimum flow rate of 7.5m3 per hour and you use 1.5 inch pipes which will give you a maximum head of 15 cubic meters per hour but you have a 20 inch filter that has a maximum flow rate of 10 cubic meters an hour then 10m3 is the highest flow rate you should be using. If you have a 30 inch filter that has a maximum flow rate of 21 cubic meters an hour than you are able to push this amount of water through. However as you only have 1.5 inch pipework there is no point going over 15 cubic meters an hour as there is only so much water you can get through the pipe at any one time.

Step 10) Flow Head

The total resistance to flow is measured in “meters of head”.  As you will notice from looking at the individual pump charts, the greater the resistance to flow (expressed in meters of head), the lower the flow rate.  The greater the resistance to flow, the more powerful the pump needs to be to overcome it.

As a general rule, most domestic pools have a head resistance of 10m. Some installations do have a larger head and some may be smaller but we take an assumption that 10m is the average.

Therefore when looking at the flow charts use 10m as the head.

Step 11) Selecting the Most Appropriate Pool Pump

Each pool pump will have a flow chart detailing which pumps have what flow rate at what head. Select a pool pump with a flow rate between your minimum and maximum allowance taking into consideration your filters maximum flow rate.

Example: Your pool has a minimum flow rate of 7.5m3 per hour and you use 1.5 inch pipes which will give you a maximum head of 15 cubic meters per hour and your filter will allow you to go up to 21 cubic meters an hour. Therefore an ideal  level for you would be between 7.5 cubic meter and 15 cubic meter per hour.

If you have a pool with no spa or other complications you can choose a pump in the lower of the ideal range i.e. 7.5 to 9 cubic meters per hour. If you have a pool/spa combination, you need to consider the flow requirements of the spa jets.  This will often push you towards a pump on the higher end of the acceptable scale.  In that case, we would look for a pump in the 12 to 15 cubic meter range.

If you have a pool/spa combination, you might want to consider a 2 speed pump.  It can run on low speed while it filters the pool, and then switch to high speed when using the spa.

Example: As you can see from the following pump graph for the Espa Silen Swimming Pool Pump range we have noted down the minimum flow of 7.5m3 per hour and the maximum flow 15m3 per hour and also the head of 10m which we get from step 10. We have drawn a line horizontally for the head and vertically for the flow rate. As you will see the vertical lines of the min and max flow rate meet the horizontal line of the head. Where they meet you will see red curves relating to 5 pump sizes. It is here where we can correctly size the pump for your pool. In the case of a pool with no spa or other complications we indicated that you can choose a pump in the lower of the ideal range i.e. 7.5 to 9 cubic meters per hour. Therefore as the vertical line of 7.5m3 touches with the red curve of the 30 (0.33hp) model we can use this. However as it will be the minimum, you may want to consider the 50 (0.5hp) model as you can see from the green vertical line this version will pump 10.5 cubic meters an hour.

All pumps are of different qualities and power so be sure to check the ratings before you decide on a pump. Please call us on 01895-672515 to discuss this in further detail.