Turnover Rate

A high turnover rate is not good for business, but it is important for pools...and unfortunately often ignored in the pool construction process. Turnover in the pool industry is defined as "The period of time required to circulate a volume of water equal to the pool or spa's volume." The minimum standards for turnover are 12 hours (per ANSI/NSPI-5 2003 standards) and 6 hours for commercial pools per the standards established by the MN Department of Health.

Turnover is important because it is much easier and efficient to filter the water than to treat it with chemicals. Pools with a longer turnover time period require more chemicals to treat the water, have more issues with water clarity, are more susceptible to problems with algae and typically take longer to open in the spring.

The incremental cost to design and install a pool with good versus poor hydraulics is minimal. 2" plumbing can carry 77% more water at the same velocity than 1.5" plumbing. 3" plumbing can carry 224% more water than 2" plumbing. The incremental cost for plumbing is pennies per foot and the labor is the same. Unfortunately, we see many pools with 1.5" plumbing that provides very limited flow. When we calculate the maximum flow they can achieve through the plumbing, we know their pool has poor circulation and most likely high operating costs.

What should you do? Our recommendation is that you insist your pool or pools are built to a high standard, or a six hour turnover rate. You should also insist that your pool contractor provide a flow meter installed visibly on the equipment pad in order to verify proper flow. Most flow meters cost a pool contractor under $70.00 and are easily installed.

The pool builder should be able to tell you what flow he or she has designed but to verify, the calculations are fairly simple. The volume of water in the pool is:  Pool surface X average water depth X 7.5 = Gallons in the pool. To determine the gallons per minute to achieve a 6 hour turnover, divide the total gallons by 360. For example, a 20' x 40' pool with a deep end of 8' and a shallow end of 3' would have approximately 33,000 gallons of water. The minimum flow to achieve a 6 hour turnover rate would be 92 gallons per minute.