Pool Pump Replacement
Before you go replacing your pool pump with whatever you can find on sale there is some mission critical information that you need to consider before you whip out your credit card. Most importantly the first three things you need to know are that there have been some major technology advancements in pool pumps recently. Next, simply replacing the pump with an identical replacement is not a good idea since who knows if it was sized properly in the first place...it did just fail right?
Finally, even if you are confident that the first two things do not apply to your situation, you still need to be aware that there are small, seemingly insignificant differences between pool pumps that you might not even notice when ordering (especially buying a pool pump online). These small differences might mean the difference between the right pump and the wrong pump for your pool.
Energy efficient pool pumps - Variable speed pool pumps have changed the game for how you circulate and filter pool water in a cost effective way. When an electric motor reduces motor speed by half, there is a non-linear drop in the electrical current the motor needs to operate. Drop the motor RPM by half, and reduce the current draw to 1/8. A full speed running pool pump might draw 10 amps of current. Turn the motor speed down to 1750 and the current draw drops to 1.25 amps. Drop the motor RPM down by half again to about 875 RPM and you are now running this motor on a meager current draw of 0.16 amps. This is 64 times less power than the motor uses at full speed. Even running your pool pump for part of the day is nowhere near to as energy efficient as variable speed pool pumps are. It is important to note that you can not simply run a pool pump on 875 RPM all the time, but when incorporated as part of a programed 24 hour filtering schedule, a variable speed pool pump will outperform single speed pumps while consuming vastly less electricity in doing so. For a more detailed breakdown of the cost saving potential read this article about how much money can you save with a variable speed pool pump?
Pool pump failure - Before you simply replace the pump you have now with an exact make and model replacement, you should realize that the vast majority of pool pumps are not actually sized for your pool system. Many builders simply offer the lowest cost pool pump available as this helps to keep the "build price" cheaper on the initial quote. Despite how important it is to avoid price shopping when looking for a new pool, the reality is that many home owners simply go with the cheapest price when having a pool built. It would be a huge mistake to just buy another pump like the own you have now without taking some time to learn how to size a pump to match your filtration needs, pipe size and current filter. If your pump lasted a really long time then this is less likely to apply to you. However if your pool pump was less than 10 years old when it died then you might want to take a closer look at your pool system before you install another new pump. Check out this article about early pool pump failure.
Pump specifications - Even if you know what you are looking for it can still be confusing and you can easily end up ordering the wrong pump. Even if you think you have found the right pump, you should still double check the model number of the pump. A full rated, max rated and uprated motor is the first way that you can trip up when looking for a replacement pool pump. To avoid confusion, look specifically at current draw specifications to compare one motor to the next as these numbers reveal the true size of the pump. You also need to be aware that a pump can come with 1.5" pipe connections, or 2" (or larger) pipe connections. Also some models of pumps are only 240 volts, where others have the option of running at 120 volts. All of this is information you need to verify before you commit to buying the replacement pump. If you are not careful it would be easy to accidentally order a pump that is not the right one, or not as convenient for you to use.
Choosing The Best Pool Pump
If you need a new pool pump, like immediately, then this list will fast track what you need to know to avoid making a poor purchasing decision. This will help you to pick a pump that is capable of keeping your pool water clean, without damaging other pool equipment you have, specifically the filter. This will also help you to understand pipe size and electrical requirements as they apply to swimming pool pumps.
Pool volume - When buying a new pool pump it is important to pick one that has the ability to filter the volume of your pool at least three times every 24 hours. Even if you choose to run your pool less than this you still need to have the ability to meet three turnovers per day to deal with situations where there is a problem with water quality that you want to resolve. So a 10,000 gallon pool must be able to circulate 30,000 gallons every 24 hours. That is 1250 gallons per hour if you run your pump 24 hours per day, or 2500 gallons per hour if you run your pump only 12 hours per day. Broken down into gallons per minute flow rate this would be either 20.8 or 41.6 GPM. For a more detailed walkthrough of this calculation you can read this article on pool filter sizing.
Pipe size restrictions - Swimming pool pumps are, largely, very powerful. Most swimming pools are plumbed in with either 1.5" pipe or 2" pipe size but the truth is that both of these sizes are too small for optimal flow dynamics. For this reason, many of the larger and more powerful pumps simply must have 2" pipe size as the absolute minimum. 1.5" pipe is not just the smaller of the two most common options...1.5" pipe is extremely restrictive to flow. With flow, there is an efficient range of flow up to a certain GPM cutoff, beyond which any increase in flow is met with sharp increase in efficiency loss due to turbulence and friction in the pipe. If you have 1.5" suction pipe(s) on your pool then you need to choose from pumps on the smaller side, conventionally 1.5 horsepower and smaller for 1.5" pipes and anything 2 horsepower or larger must have 2" pipe size at the minimum. Pipe sizes which are too small can cause the larger pumps to starve for water, cavitate, and potentially fail early.
1.5" Pipe = 37 GPM
2" Pipe = 62 GPM
Physical maximum flow @ 30 PSI pressure
1.5" Pipe = 94 GPM
2" Pipe = 200 GPM
Choosing a pump that has the ability to filter the volume of your pool up to three times every 24 hours, while staying within the "efficient range" of flow based on the pipe size you have is important for both flow efficiency, but also safety. It is important to not exceed the designed safety limits for suction in swimming pool pipes to avoid the potential for an entrapment hazard in the pool. Pool suction pipes should never exceed six feet per second of water velocity. This, along with efficiency, are the main reasons why you should stay within the "efficient range" provided above. Also, despite how little you think that you need to filter your pool water, three turnovers per 24 hours is still reduced from the emerging industry standard of a six hour turnover value, or four turnovers every 24 hours so there is no reason to use less than three for your calculations.
Filter maximum design flow rate - All pool filters will have a maximum designed flow rate beyond which there is the distinct possibility that you will damage the filter, the filter media, or compromise the ability for the filter to keep your water clean...or potentially all of these things. You need to calculate your system flow rates, and then double check that you will not be exceeding the maximum design flow rate for your filter. Sand filters in particular are of serious concern as they tend to have much lower maximum designed flow rates than other types of pool filters. To see all filter listings for maximum flow rate you can read this article about pool filter reviews.
Electrical requirements - Most pool pumps will require 240 volts due to the heavy current demands from pool pump motors. Small motors up to around 1 horsepower, or 1.5 horsepower, typically can work with 120 volt circuits, but any larger and you must use 240 volts. If you are not sure what you have now you should double check. All houses have 240 volt and 120 volt circuits. If you are not sure what you have now you can have an electrician test it, or you can look at the electrical breaker. 240 volt breakers are twice as wide as the more common 120 volt breakers. If you have 240 volts available then you should likely be able to use any pump. If you only have 120 volts available then you need to either upgrade your electrical service to the pump, or select from the 120 volt compatible pumps.
How to know which pool pump to buy?
The final step in choosing the best pump replacement is to put the information listed above together in a way that helps you. When choosing your pump you must choose one that can work on the size of pipes that you have. This is a hard rule. If you have 1.5" pipes then your pump should not run more than 37 GPM. This means an eight hour turnover rate of 17,760 gallons. If you have 2" pipes, then you should not exceed 62 GPM. This equals 29,760 gallons based on an eight hour turnover. Running a more powerful pump and exceeding these flow values is inefficient and possibly dangerous. Once you have determined what flow rate your pool needs to meet the eight hour turnover rate minimum, you need to make sure this number does not exceed the flow rate for your filter.
2" pipe size
Filter maximum designed flow rate 82 GPM
The 2" pipe will allow up to 62 GPM efficiently. The pool needs up to 60,000 gallons through the filter every day to meet the eight hour turnover requirement. If you run your pump 12 hours per day this means you need to filter 60,000 gallons in 12 hours, or 83.3 GPM for 12 hours every day. As you can see from this example the flow velocity of the water will need to exceed the recommended maximum of 62 GPM. It will also slightly exceed the maximum designed flow rate for this filter. This means that it would be better to run the pump longer, and with slightly slower water velocity. The only problem is that pool pumps, for the most part, can't do that. This is the breakdown in this calculation, in that you can not simply tell your pump to produce 62 GPM and no more. Unless the pump allows you to control the motor RPM you will have no control over the flow rate of the pump...only how many hours per day you let it run. Also, most single speed pool pumps will produce far more flow than you want. Take a look at this page that shows expected flow rates for single speed pool pumps.
A well designed pool filtration system can have the missing elements that make this calculation more difficult than it needs to be. Consider adding a variable speed pump to your filtration system to experience less electrical costs for running your pump, and install a flow meter into your system to allow you to monitor actual water flow rates in your system. Once you understand why your pool needs to turnover the water at least three times every 24 hours, and that slower pumping water is more energy efficient than fast moving water, picking your next pool pump becomes easy.
Use this quick reference to find the best VS pump for your pool: Which is the best variable speed pool pump?. Despite how many VS pump options there are on the market currently, the majority of pool owners will end up choosing one of the few listed on that page.
Variable speed pump reviews
What is the best variable speed pool pump?
Maximum designed flow rate for all filters
How to size a filter for your pool
Flow meters for swimming pools
If you want to continue learning about pools and spas from an industry expert follow swimming pool Steve on acebook , twitter and youtube