This is a question that we should be getting everyday, instead we usually get "which pool pump is cheapest?".  The proper question to ask is "Which pool pump is my best value?". best Value and Cheapest are never the same.  CHEAPEST means that your upfront costs will be less, but usually means that your long run costs are more.  BEST VALUE means that you are getting the best value today and for the long run.

The best way to choose the BEST VALUE for your pool is to determine the proper turn over needed to keep your pool clean and sanitized.  First we will need to know the gallons of water your pool holds. To determine this we will use one of the following formulas:  The most often used is Length X Width X Average Depth X 7.5 = Total Gallons.

A typical 16' X 32' Pool that is 6 feet at its deepest point will hold about 17,000 gallons of water.  Next we will need to determine proper turn over rate.  it is recommend that the pool filter completely the entire pool every 6 hours or at least twice a day. This pool would require a pump with a minimum of 48 gallons per minute (gpm), to run 12 hours per day.   

Now it is time to pick a pump.  You will want to look a variety of manufactures and the different model pumps that they offer.   To determine the best pump for your pool you will need to read a Pump Curve Chart.  This will help you to identify which size pump is needed to deliver the required gallons per minute.  You will also need to know the Total Dynamic Head (TDH) of your pool system.  Most pools TDH will range somewhere between 40 to 60 feet of head.  This is the amount of Friction or back pressure developed in the pool plumbing when the pump is running.  The larger the pump that is installed on your system the more TDH that will be produced.  It is always best to properly size your pool pump for proper Circualtion and Efficiency.  Let's start with one of the most common pumps on the market, the Hayward Super Pump.  To produce a minimum of 48 gallons per minute (gpm) We would need at least a 1 Horsepower pump. This would be at an average of 50 feet of TDH or Total Head. This pump would produce right at 48 gallons per minute. 

The next pump we are going to look at is the Pentair Whisper-flo.  This is also a very common pump on most pools. With this pump we would only need a 1/2 horsepower pump to produce our minimum of 48 gallons per minute (gpm)  This actual pump will produce about 55 gallons per minute at 50 feet to Total Head (TDH) or Feet of Water.

As you can see the Whisper-flo will produce 55 gpm with a 1/2 hp motor where the Super Pump will produce 48 gpm with a 1 hp motor.  The lower the horsepower the better the Energy Savings.

Now lets look at a much larger pool.  a 20' X 40'  with 8 feet of depth at its deepest point.  This pool would hold 33,000 gallons of water. For a proper turn over of 92 gallons per minute.  Looking at the same charts the proper sized Hayward Super Pump would be a 2 hp pump that would produce about 88 gallons per minute (gpm).  The proper Pentair Whisper-flo would be a 1 horsepower that would produce about 88 gallons per minute.  That is half the horsepower.

According to APSP-15 (Association of Pool and Spa Professionals) which has been adopted by the International Building Code, they require any pool needing a 1 horsepower pump or more to have a Two Speed or Variable Pump Installed.  These pumps would enable you to run your pool for 24 hours at a much slower speed, enabling you to turn over your pool twice every 24 hours.  This will actually use significantly less energy than running the larger single speed pump for 12 hours per day.  

I hope that you have found this useful.  When building your pool or replacing your pump, always remember to look for your BEST VALUE! The CHEAPEST PRICE  will always cost you more in the long run.