How do I size pumps and filters for swimming pools?

How do I size pumps and filters for swimming pools?

Sizing of pumps and filters for swimming pools is dependent on the size of the swimming pool, i.e. volume of water, and the expected usage of the swimming pool.

Calculating the volume of a box-shaped swimming pool is easiest.  The volume of the pool will be length x width x depth.  For a pool with a slanted slope, we use the average of the lowest and highest depth of the pool.  For example, given a pool 10 feet wide and 20 feet long, with its shallowest depth at 3 feet and a maximum depth of 5 ft, the volume in cubic feet is 10 x 20 x ((3 + 5) / 2) = 800 ft³.  1 ft³ = 7.48 US gallons, so 800 ft³ is around 5984 gallons.

Expected usage affects the sizing of pool equipment because it dictates the duration by which the whole pool water volume should be filtered.  This is called the turnover cycle.  For residential use, 8 hours turnover cycle is normally used.  For commercial use, i.e. resorts and hotels, 6 hours turnover cycle is used.

The swimming pool pump must be able to circulate the pool water volume within the turnover time.  Pool water will pass through the filter once per turnover cycle.  Thus both the pump and filter must be able to handle a flow rate of (water volume / turnover cycle).

For our previous example, volume = 5984 gallons.  For residential use, required flow rate = 5984 gallons / 8 hours = 748 gph or 12.47 gpm.  For commercial use, required flow rate = 5984 gallons / 6 hours = 997.33 gph or 16.62 gpm.

Pool pumps and filters are given gpm ratings.  A properly sized pump will have a gpm nearest the required flow rate.  A properly sized filter will be the smallest filter that equals or exceeds the pump's actual flow rate.