How to Choose a New Pool Pump: Types, Sizing and What to Check Before You Buy

Last updated: September 2026

If you’re reading this, chances are your pool pump is on its last legs, or you’re building a pool and staring at a wall of pump specs. Choosing one can feel confusing, but it doesn’t need to be. By the end of this guide you’ll know what type to buy, how to size it and what to check before you hand over your money.

The pump is the heart of your pool. It drives the filtration, the heating and the sanitising. Without it, you’ll soon see your pool turn green. This post is about choosing the right pump. If you want the numbers on what a pump costs to run, and why the cheap one often isn’t, read the companion post: Swimming pool pumps: the shocking truth about running costs.

Types of pool pump

There are three types of pool pump: single speed, dual speed (two-speed) and variable speed. Here’s how they compare:

Type	How it works	Upfront cost	Running cost	My view
Single speed	One fixed speed, always flat out	Lowest	Highest	Only for very small pools or seasonal use. Being phased out in the USA.
Dual speed	High and low fixed speeds	Middle	Middle	Better than single speed, but you’re stuck with two settings.
Variable speed	Any speed in its range, with its own controller and timer	Highest	Lowest	The best choice for almost every pool. Quieter too.

The reason variable speed wins is simple physics. ENERGY STAR explains that “reducing pump speed by one-half allows the pump to use just one-eighth as much energy”. Running slowly for longer moves the same water for a fraction of the electricity. I’ve put real UK and US numbers on that in the shocking truth.

What the law says

• USA: the Department of Energy’s efficiency standard for dedicated-purpose pool pumps applies to pumps manufactured from July 19, 2021. The standard is based on efficiency (a “weighted energy factor”), not a speed rule as such, but in practice in-ground filter pumps over 1.0 total horsepower now need to be variable speed to pass. Spa circulation pumps and pumps labelled as waterfall pumps are excluded. On top of that, a 2023 rule on replacement pool pump motors requires motors from 1.15 to 5 total horsepower to have variable-speed capability from September 29, 2025. So even swapping just the motor now pushes you towards variable speed. Some states have their own rules on top, so check locally.
• UK: I’m not aware of an equivalent rule forcing variable speed on domestic pools. The choice is down to you, and running costs make the case on their own.

Sizing: how much flow do you need?

Bigger isn’t better with pool pumps. An oversized pump costs more to buy, costs more to run, can exceed what the filter is rated for and makes a racket. Size it for the job.

Step 1: work out your volume

Length x width x average depth. For example, 8m x 4m x 1.4m average = 44.8m³, or about 45,000 litres (roughly 11,900 US gallons). In feet: length x width x average depth x 7.48 gives US gallons.

Step 2: pick a turnover time

Turnover is how long the pump takes to push the whole volume through the filter once. ENERGY STAR’s pump criteria use a 12-hour turnover (from the US residential pool standard ANSI/NSPI-5) as the minimum filtration speed. For most home pools I’d design for one full turnover in 8–12 hours of running a day, then fine-tune it by watching the water.

45,000 litre (11,900 US gal) pool	Flow needed
12-hour turnover	3.75m³/h (about 17 GPM)
8-hour turnover	5.6m³/h (about 25 GPM)
6-hour turnover	7.5m³/h (about 33 GPM)

That’s far less flow than most people expect, and it’s why a variable speed pump ticking over quietly for most of the day is the efficient way to do it. You’ll want higher speeds for vacuuming, backwashing, a water feature or a spillover, and that’s where a variable speed pump earns its keep again, because you only run fast when you need to.

The US Department of Energy’s advice on choosing and operating an efficient pool pump is to start at around 6 hours of filtration a day and adjust in 30-minute steps. In a Florida study it quotes, most pool owners cut pumping to under 3 hours a day with no loss of water quality. Clear water is the test, not the clock.

Step 3: allow for resistance (head)

A pump’s flow drops as the resistance in the system rises: the pipe runs, the fittings, the filter, the heater and any height the water has to climb. Every pump has a performance curve that shows flow against head. Estimate your system’s head (or ask your supplier to), and pick a pump that delivers your target flow at that head, not the headline “maximum flow” on the box.

You can cut the resistance too. The DOE says a filter rated at least 50% above your design flow, bigger or shorter pipes, and 45° bends instead of 90s can reduce electricity use by up to 40%.

Where will the pump sit?

• Above the waterline: you need a self-priming pump. It has a strainer pot that holds water so it can pull a vacuum and lift water up to itself. Almost all pool pumps are self-priming, but check.
• Below the waterline: the pump is flooded by gravity and primes itself. A self-priming pool pump still works fine here. Just fit valves either side so you can service it without draining the pool.

Hot tub pumps are a different story. Most aren’t self-priming, which is why they have to sit below the water. See self-priming hot tub pump options if your control room ends up above the waterline.

Match it to the rest of your system

• The filter. Every filter has a maximum flow rate. Don’t exceed it. A sand filter is the usual choice on a pool. See Sand filters explained.
• The heater or heat pump. Heat pumps and heaters have a minimum and maximum flow, usually protected by a flow switch. If you run a variable speed pump too slowly, the heat pump can stop heating. Check the manufacturer’s figures and set a heating speed that satisfies them. See how to choose the right air source heat pump for your hot tub or pool.
• Salt chlorinators and UV often have minimum flows too.
• Pipe and unions. Measure the pipe connections. In the UK, 50mm metric and 2in imperial pipe look almost identical but aren’t the same size. See pump union sizes explained.
• The electrical supply. UK pumps run on 230V 50Hz. In the USA, many variable speed pumps are 230V, some are dual voltage and some are 115V, so check what your circuit provides. A motor built for 60Hz won’t perform the same on 50Hz, so buy equipment made for your country.
• Controls. Most variable speed pumps have a built-in timer with several speed programmes. If you have pool automation, check the pump can talk to it (by relay inputs or the maker’s own protocol) before you buy.

Replacing a like-for-like pump

If you’re swapping out an old pump, take these off the old one first:

• The make and model, and the horsepower and service factor from the rating plate.
• The voltage and the full-load amps.
• The suction and discharge connection sizes, and their height from the floor (so the new one lines up with your pipes).
• Whether it’s above or below the waterline.

Moving from single speed to variable speed, you don’t usually need the same horsepower. A variable speed pump spends most of its life at low speed anyway. Just make sure its top speed covers the jobs that need high flow, such as backwashing, a spillover or a cleaner.

Other things worth checking

• Noise. Variable speed pumps are much quieter at low speed. If the equipment is near a bedroom window or a neighbour’s fence, check the maker’s quoted noise level at the speed you’ll actually use.
• Build quality. Look at the materials (motor, seal, housing, lid) and the warranty. There’s more on cheap versus premium in the shocking truth.
• Parts availability. Can you get a seal kit, a lid O-ring or a basket in five years’ time? Established brands usually win here.

Which brands?

For variable speed pool pumps, the big names I’d look at are:

• Pentair: known for reliability and a wide range of variable speed models.
• Hayward: a big range with good durability and parts support.
• Jandy: strong on integration with its own automation systems, so a good pick if you want smart control.

There are good lesser-known brands too. Judge the pump on its curve, its efficiency, its warranty and parts support, not just the name. For UK pumps, have a look at the pumps section on parts4tubs.co.uk. In the USA, head to parts4tubs.com.

Common mistakes

• Buying on horsepower. More horsepower isn’t better. It usually means more noise and bigger bills.
• Ignoring the filter’s maximum flow.
• Running a variable speed pump so slowly that the heat pump or salt cell doesn’t see enough flow.
• Using a pool pump to drive hot tub jets. Jets need around 10 GPM each at a decent pressure. A pool pump moves lots of water at low pressure, so the jets feel weak. See Can I use a variable speed pump in a hot tub? and how to size a hot tub pump.
• Putting a pump that isn’t self-priming above the waterline.
• Forgetting the valves. Without them, changing the pump means draining the pool.

Troubleshooting a new pump

Problem	Things to check
Won’t prime	Strainer pot filled with water, lid O-ring clean and lubricated, suction valves open, air leaks on the suction side, water level halfway up the skimmer
Air bubbles in the pump basket	Suction-side leak (unions, lid, valve stems) or low water level
Heat pump shows a flow error	Pump speed too low for the heat pump’s minimum flow, or a dirty filter
Filter pressure creeping up	Filter needs backwashing or cleaning
Noisy	Cavitation from a restricted suction, worn bearings, or a pump not bolted down properly. See noisy pump? How to diagnose it

Planning a pool or plunge pool build?

If you’re building from scratch, the pump is just one part of getting the hydraulics right. My plunge pool and cocktail pool plans and swim spa plans come with the plumbing diagrams and a full parts list, so the pump, filter and heater are matched for you. For something custom, draw it in the free Tub & Pool Designer Pro software and I can turn it into architectural CAD and a 3D plumbing design.

FAQs

What size pool pump do I need?

Work out the flow to turn your pool’s volume over in about 8–12 hours, then choose a pump that delivers that flow at your system’s resistance. A 45,000 litre (11,900 gallon) pool needs only around 4–6m³/h (17–25 GPM) for filtration.

Is a variable speed pool pump worth it?

For almost every pool, yes. Halving the speed uses about an eighth of the energy, so it pays back through lower bills, and it’s much quieter. In the USA, most new in-ground filter pumps have to be variable speed anyway.

How many hours a day should I run my pool pump?

Enough to keep the water clear. The US DOE suggests starting at around 6 hours and adjusting in 30-minute steps. With a variable speed pump, you’ll usually run it longer at a low speed.

Do I need a self-priming pump?

Yes, if the pump sits above the water level. Below the waterline, the water flows to the pump by gravity.

Can I use a pool pump for hot tub jets?

Not well. Pool pumps move lots of water at low pressure, and jets need pressure. Use a proper hot tub jet pump.

Stuck choosing between two pumps? Drop the details in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

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