A swimming pool pump circulates water through the pool's filtering system, mixing chemicals and sanitizing the water to keep it free of contaminants and debris like algae and bugs. It's important that your pump be properly sized to your pool so this cleaning system operates efficiently. This guide will help you match the size of your pool to the pump you need to deliver the right amount of circulation while maximizing safety and savings.
Sizing the Pump for Your Swimming Pool
While you might think bigger is better, the truth is that a pool pump that is too big for your pool can cause serious problems, like cloudy water and damaged filters. Oversized pumps also waste energy and money. Replacing an oversized pool pump with a high-efficiency unit can pay for itself in energy savings and reduced power bills in just a few years. The four factors you need to know to size the pump that's right for your pool are:
1. Pool capacity
2. Flow rate and turnover
3. Maximum flow rate
The first step in sizing your pool pump properly is knowing the volume of water in your pool.
Step 1: Calculating Pool Capacity
To determine your pool's volume accurately, you need to factor in the pool's average depth using this formula:
|1||Measure the shallow end depth:||4'|
|2||Measure the deep end depth:||+ 12'|
|3||Add them together:||16'|
|4||Divide by 2:||16 ÷ 2 = 8'|
This pool's average depth is 8'
Now use the formulas below to determine the volume of water in your pool:
Diameter (ft.) X Diameter (ft.) X Average Depth (ft.) X 5.9 = Total Pool Capacity in Gallons
Length (ft.) X Width (ft.) X Average Depth (ft.) X 6.7 = Total Pool Capacity in Gallons
Length (ft.) X Width (ft.) X Average Depth (ft.) X 7.5 = Total Pool Capacity in Gallons
Once you know the volume of water in your pool, you're ready to calculate the flow rate and turnover required to circulate the water in the number of hours you want.
Step 2: Calculating Flow Rate and Turnover
Flow rate is simply the number of gallons the pump moves per minute. Turnover is the minimum amount of time it takes to circulate all the water one time through your pool's filter. In general, an average turnover of every 6 to 8 hours is sufficient for most pools.
Use this formula to determine your turnover rate:
Pool Volume in Gallons ÷ Turnover Rate in Minutes = Flow Rate
Example: If you have a 25,000 gallon pool, and you want the water to turnover once every 8 hours:
25,000 ÷480 (60 minutes X 8 hours) = 52 gpm
Your 25,000 gallon pool needs an output of 52 gallons per minute to circulate the water once every 8 hours.
Step 3: Calculating Maximum Flow Rate
The size of your pool's pipes determines the maximum flow rate in your pool. Count your pool's number of intake lines and refer to the common pipe sizes below:
• For each 1.5" intake line, the maximum flow rate is 42 gpm.
• For each 2.0" intake line, the maximum flow rate is 73 gpm.
Two 1.5" intake lines = 84. The maximum flow rate is 84 gpm.
This number is important because your pool filter has a maximum flow rate, which is measured in gpm. The pool pump's gpm rating should be below the pool filter's maximum flow gpm rating. If the pool's turnover rate is higher than the filter's maximum gpm, the filter is undersized and will not work properly or become damaged. If the filter is undersized, it should be replaced, or the pump should be undersized to prevent damage to the filter.
Step 4: Calculating Resistance
Every piece of swimming pool equipment connected to your pool's circulation and filtration creates resistance to water flow. This includes the length and size of the pipe, the type of filter and features like heaters and pool cleaners. The total amount of resistance is called "feet of head"; the greater the feat of head, the stronger your pump needs to be to overcome it. Even if you have an older pool and don't know some of these factors, it's possible to determine the pool's feet of head. Use a pressure meter and this formula:
• Check the pressure of water flowing into the filter tank and multiply that number by 2.31.
• Get a vacuum reading on the pump suction line and multiply that by 1.13.
• Add the two numbers together and the result is the total dynamic head.
If the water flowing into the filter tank is at 10 PSI, and the vacuum reading on the pump suction line is at 5 PSI:
Water flow into filter tank: 10 PSI x 2.31 = 23.10
Vacuum reading on pump suction line: 5 PSI x 1.13 = + 5.65
Total resistance = 28.75 ft. of head
Select the Pump You Need
Now that you know the number of gallons of water in your pool, the flow rate required for the turnover you want, the maximum flow rate in relation to your pool filter and the feet of head, you can use pump manufacturer performance charts that identify the model and horsepower appropriate for your pool. These models vary from manufacturer to manufacturer, so be sure to check each manufacturer's documentation and don't assume information from one chart correlates to another.
Pool Cleaner: Vacuums dirt and debris from pools. Models range from manual to robotic cleaners that clean the pool automatically in as little as three hours.
Skimmer: These easy-to-use hand-held nets make cleaning the surface of your pool a breeze.
Thermometer: Lets you check the pool's temperature before you take a dip.
Pool Test Kit: Check the chemicals, alkalinity and pH balance in your pool with a pool test kit to maintain safety and water clarity.
Safety Alarm: Sounds a loud alert when someone falls into the pool. Essential for families with small children and pets.
Not all of these pool accessories may be available online. Check availability at your local The Home Depot store.