There are few things better than taking a dip on a hot summer day in your own backyard. Keeping your pool clean and safe is essential for getting maximum enjoyment for you and your loved ones- part of that relies on having the right pool pump.
Understanding pool pump horsepower and size helps owners find the best equipment for their pool- and keep it running smoothly for those sunny afternoons.
What is Pool Pump Horsepower?
Horsepower is a measure used for the strength and power of your pool pump. It is the most important rating on your pump- and directly impacts how well your pool water is circulated and cleaned.
How Pool Pump Horsepower Affects Flow Rate and Head Pressure
In general, a higher HP pump has a higher GPM flow rate (gallons of water per minute). This refers to how quickly the pump can circulate the water in your pool.
It also means a higher head pressure- meaning the distance between where the water flows and is discharged. High-head pumps are better in pools with a more complex plumbing system, water features, heating, or built-in cleaning systems.
Factors that Affect Horsepower Requirements
- How many gallons of water your pool holds
- The target flow rate of your pool filter system
- Minimum and maximum flow rates for your pool water
- What pressure your plumbing can handle
Recommended Horsepower for Different Pool Sizes and Types
Do not be fooled into thinking that bigger pools need a bigger pump- that is not necessarily the case. Remember, the bigger the pump, the more energy it is likely to use- upping your expenses perhaps more than they need to be.
The goal should not be to get the biggest pump you can afford- it should be to get the pump size that does what it needs to do for your pool at the lowest cost.
Of course- you also don’t want to go too small. If your pump is not big enough or powerful enough, you risk algae buildup, moss, and nasty bacteria sitting in the water.
To find the best-size pool pump, you first need to measure your pool for the volume of water it holds. A simple calculation for determining water volume in a rectangular or square pool is:
Pool Length x Pool Width x Average Depth
Using these measurements, you get a pretty accurate idea of how many gallons of water there are in your pool, and from there, you can choose the right size pool pump.
Circular pools are a little more complex. In that case, the calculation is:
3.14 x Radius Squared x Average Depth x 28.13
Don’t worry too much if you are not a math whiz- it may look complex, but it is still a simple calculation. To work out the radius, measure the widest part of your pool and cut it in half. Next, you square it (times it by itself). If the width is eight meters, the radius is four meters- so the radius squared is 16 meters.
Once you know the rough volume of your pool, you can find out what pool pump size you need. The recommended turn-over time for pool water is between six and eight hours- so you need a pump big enough to circulate the full volume of your pool in that time.
How do you work that out? Just divide the volume by the number of hours, and find a pump that can move that amount of water in a single hour. Most pool pumps measure the gallons of water moved per minute, so divide the number by 60, and you have your recommendation.
Here is a rough guide of pool pump horsepower to pool size.
- Less than 15,000 gallons: 0.5-0.75 HP
- More than 15,000 gallons: 1-1.5 HP
- More than 17,000 gallons: 2-3 HP
These are rough guides- and there are many things to consider, so try to take everything into account.
Single-Speed Pool Pumps and Horsepower
Single-speed pumps are the least expensive option- but they also have the most basic technology. They are great if you know exactly what your pool needs and live in a place where weather conditions don’t change all that much throughout the year.
As the name suggests, they run on one speed setting- and you can’t adjust it. They are not as popular as they once were, with more pool owners opting for energy-efficient, adjustable options.
Dual-Speed Pool Pumps and Horsepower
A step up from single-speed pool pump models, we have dual-speed. These come with two settings, increased efficiency- and often lower noise levels. It is good to have the option to switch to a lower setting sometimes- especially when your pool is not in use.
Variable-Speed Pool Pumps and Horsepower
The third option is a variable speed pump. They are the most expensive option overall- but they also have the most benefits.
You can set the pump to multiple speeds to cope with various conditions- adjusting the flow rate, max horsepower, and of course- speed.
Variable speed pumps are generally the best choice for many pools. Because you can adjust the settings, you can get away with going for a bigger pump with more horsepower- then fine-tune it to suit your pool.
A variable speed pump works for in-ground and above-ground pools, uses modern technology, and can sometimes save you a lot of money.
Choosing the Right Horsepower for Your Pool Pump
When choosing the best horsepower rating for your swimming pool pump, you need to consider the following factors.
- Pool volume in gallons (to determine how much water needs to be filtered every day)
- Minimum flow rate (for efficient water cleaning)
- Maximum flow rate of the pump (what is the most it can do)
- The ideal flow rate for your filter (based on the gallons in your pool)
- Whether or not you need TDH or plumbing resistance
Oversizing vs. Undersizing Horsepower
A surprising number of pools do not have the correct size pump in terms of horsepower. Oversizing is quite a big problem- because people think that more horsepower must mean better performance.
Newly built homes with pools often have oversized pumps because horsepower sells. It sounds good to say, ‘It has a two-HP pump installed’- when, in reality, that could be far more than it actually needs.
The downsides of oversizing include:
- Too much pressure on the plumbing
- Excessive and unnecessary energy usage
- Noisier motors
On the other hand, an undersized pump is unlikely to efficiently clean your pool- at it could break quickly because it is being seriously overworked. Most pools don’t need high horsepower, but if it isn’t enough, you could be in trouble.
The main issues with undersized horsepower pumps are:
- Overworked motors
- Insufficient maximum flow rate
- Algae build up in water that is left stagnant
- They can’t handle the resistance pressure
Ideally, your pump should be neither oversized nor undersized, which is why there are so many detailed calculations available to determine how much horsepower you need.
If you are unsure, it is better to err on the side of caution and go for a bigger pump rather than smaller. It is better to overpay a little on electricity bills than face expensive maintenance and repairs for an algae-riddled pool. Just don’t go too far- very few standard home pools that don’t have water features require anything more than 1.5 HP.
Energy Efficiency and Horsepower
Speaking of energy efficiency, the horsepower rating of your pump will affect your usage. High-horsepower motors use more energy- but there are ways to minimize it for better efficiency.
Using a variable speed pump with decent horsepower is the best choice for energy efficiency overall. You get the benefits of a powerful pump, but you don’t need to run it on max all the time. Many modern pumps are designed to automatically switch to the most efficient setting unless manually changed- so they can save you a lot of money over time.
A low horsepower pump may not use as much energy, but if it is having to work overtime to keep up with the demands, it is still going to end up costing more than it should- without even doing the job properly!
Cost Considerations and Horsepower
Cost matters- and finding an affordable pump that does the job is always beneficial. There are a few things that impact the prices of pumps- including horsepower.
High-horsepower pumps are usually more expensive- especially if they have variable speed settings. That said, they pay themselves back quite quickly if you consider the energy savings- especially if you use your pool all year round.
Noise Level and Horsepower
Another reason not to buy a pool pump with more horsepower than you need is the noise level. As expected, more horsepower usually means more noise- that is just the way it goes.
Although many modern models are designed with noise control features, a 2HP pump is almost always going to be louder than a 0.75HP pump- unless the little one is broken.
Maintenance Requirements and Horsepower
Looking after a swimming pool and pool equipment can be a time-consuming task, but it is vital to keep your swimming pool water clean, safe, and enjoyable. In general, pumps with higher speeds wear out faster and require more maintenance- which is why you don’t want to get one that is bigger or more powerful than it needs to be.
Pool Pump Horsepower and Electrical Requirements
The more powerful the pump, the more electricity is uses, and the higher your energy bills will be. High-horsepower pumps use a lot of electricity- so don’t go bigger unless you need to.
Horsepower and Pool Pump Performance
A higher horsepower pump can clean a pool more quickly- but that doesn’t always equal better performance overall. Sure- it will turn over and filter the water pretty well, but it can also cause issues in your plumbing system if the power is too high- which could lead to a serious drop in performance- and some pretty pricey bills.
On the other end of the scale, a pump with a horsepower rating that is too low for your pool will not perform well. It may not be able to reach all the water- leaving stagnant sections and potentially dangerous bacteria to stay in the pool. It may also wear down quickly from being overworked.
Picking the perfect pump for your swimming pool is quite tricky when you break down the math behind the decision- but with this rough guide, things should be a little easier. Your pool pump sizing
Horsepower directly impacts how your pool pumps perform. Too low, and the water in your pool can become stagnant and dirty- too high- your energy bills can soar, and your plumbing can suffer.
The most important thing is the take the correct measurements and find a pump that fits.