Selecting the right Pool Filter Size

Getting the right size filter for your pool is important for keeping your pool clean, and for saving money. While a pool specialist can help you calculate the correct pool filter size for your particular pool or spa, below are the steps to help you figure it out on your own.

To properly size and select the filter for your pool or spa, you must:

1. Calculate your pool's volume. 2. Calculate your pool’s capacity. 3. Calculate your pool’s flow rate. 4. Calculate the filter flow rate.

Calculating the Volume The first step in finding the correct filter model is to figure out how much water has to be filtered. Below are the formulas to use when calculating the volume of a swimming pool:

For a rectangular pool: Multiply the length by the width by the average depth • (L x W x D).For a circular pool: Multiply the radius of the pool (half of the diameter) by 3.14 (pi) by the average depth. • Radius x depth x 3.14 For Oval shaped pools: Use the grid technique. (since an oval is closer to a rectangular shape with semi-circles on the ends). Make a drawing of the pool on a piece of square-grid graph paper, with each square representing one square foot . Count up the number of squares, including those partially filled, to give you a close estimate of the pool's square footage area. Multiply the area by the average depth of the pool. • Area x Depth

Calculate The Capacity The capacity of your pool is the number of gallons of water that your pool will hold. To calculate the capacity: Multiply the pool volume by 7.48 (the number of gallons of water contained in a cubic foot of volume). • V x 7.48

Calculate The Flow Rate The flow rate is the volume of water flowing past a given point (for example: your filter) during a specific period of time. The flow rate is measured in either gallons per minute (GPM). To calculate the flow rate: Divide the capacity of the pool (calculated above) by the turnover rate (the time required to circulate a body of water equal to the capacity of the pool). * A good rule of thumb might be to use 8-12 hours as your turnover rate.

Calculate The Filter Flow Rate The filter flow rate is the amount of water filtered over a given period of time - expressed in gallons per minute (GPM). To determine the filter flow rate: Multiply the filter area by the filter rate. (you can get both figures from the filter manufacturer). With both of these numbers, you can calculate the filter flow rate to see which particular filter will match your needs. FINAL NOTE *You may want to go a little larger on your filter than your actual flow rate needs.

When selecting the right-sized filter, it is important to keep in mind that as the filter removes debris from the water, the filter medium will become more and more clogged, and the filter will require an ever greater flow to clean an equal amount of water. To allow for debris buildup and backwashing, you may want to overestimate your flow rate, which would mean you would get a slightly larger filter with a higher filter flow rate.

Contact Swim Smart Pools and Spas for more information.