How to Measure Through-the-Wall Pool Skimmers

Calculate the volume of water in the pool. The formula is length times width times depth for a rectangular pool that doesn't change depth. For a traditional rectangular pool that gets deeper at one end, the formula is (length times width times depth of the shallow end) plus (1/2 times width times the difference between the shallowest depth and the deepest depth times the distance from where the shallow end begins to get deeper to the edge of the deep end). For circular pools with a consistent depth, the volume would be the depth times 3.14 times the square of the radius, which is the distance from the middle of the pool to the edge of it. For odd-shaped pools, you may need to consult with the manufacturer or a manual that comes with it for the approximate volume.

Calculate the turnover rate by dividing the number of gallons in the pool by the hours recommended for that individual pool's filtering. For instance, a public pool may be turnover-rated for six hours while a backyard in-ground pool may require four hours and a small spa pool may require one hour. A pool containing 24,000 gallons and requiring a four-hour recycling time will have to move 6,000 gallons per hour to turn over the water in four hours.

Divide the hourly water-removal figure by the number of through-the-wall skimmers in the pool to determine the required rating. For instance, if there are two skimmers, each must be rated for 3,000 gallons per hour.