Guide written by:
Patrick, Handyman, Bath
Whatever type of pool you have, you'll need a decent pump to ensure a good filtration and quality pool water. From flow rates to power ratings, self-priming or otherwise, allow us to "clarify"!
- Flow rate
- Noise level
- Power rating
What's a pool pump for?
The function of a pool pump is to circulate water in the pipe network of your swimming pool. It draws in water from the pool basin via the skimmers and drain opening, passes it through a filter and in some cases a disinfection system, then releases the water into the basin via discharge nozzles. This procedure has the effect of purifying the water and removing suspended particles.
Depending on your setup, a pool pump can also be used to operate a pool robot or release bubbles via massage nozzles.
It is also essential for washing and rinsing the pool filter.
The pump is typically the only mechanical element of a home swimming pool installation.
As a result it's the part of your pool that's most likely to go wrong. And when we say go wrong, we mean filtration failure and cloudy, dirty pool water in no time...
What are the key factors when choosing a pool pump?
Three essential criteria should be considered when working out what you need from your pool pump:
- Maximum flow the pump can produce;
- Reliability and quality of manufacture;
- Noise level.
How to calculate the flow you need?
The flow rate you require will depend on the characteristics of your pool.
To preserve an adequate quality of water, the filtration cycle must be capable of processing and filtering all the water in the pool in under six hours, four being optimum.
Example: for a rectangular pool 8m x 4m in size, with an average depth of 1.5 m, pool volume is 48m3; so you want a pump flow of at least (48 / 4 =) 12m3/h to enable complete recycling of the water within four hours.
However, this is a minimum, and it's always better to oversize your pump capacity. Without launching into a crash course in hydraulics, let's just say that water circulation can encounter various forms of resistance; so a good rule of thumb is to oversize the rated flow of your pump by a factor of 1.2 to 1.5.
Various specific factors may warrant additional pump capacity:
- Pool piping layout - the more bends there are, the more the flow of water is resisted;
- Distance between the pool and machine room - the further it is, the more powerful the pump has to be;
- Pump height in relation to the skimmers - just like increasing the distance, making the pump push uphill will require more power;
- Filter volume and clogging - since passage through the filter produces resistance, which increases as it becomes clogged with debris.
In our case, for a pool basin with a machine room slightly above the level of the pool and 8m away horizontally, a pump with a minimum flow of 15m3/h will be ideal.
If you really want to get into the nuts and bolts, refer to the manufacturer's charts provided with the pump which give flow figures according to system pressure. This will allow you to make precise comparisons between different models of pump, but short of having a very sophisticated installation, the simple methods of calculation mentioned above will do just as well.
Where can I find the flow rate of my pump?
Just look at the label on your pump or, failing that, at the user manual!
The flow rate given on the pump corresponds to a certain pressure in the circuit - and this is where you need to be careful.
The flow rate we calculated above is for pressure between 0.8 and 1 bar. If the flow rate given by the manufacturer corresponds to a lower pressure value, actual flow will be lower at 0.8 bar (since the pump will effectively be pushing against more resistance). You'll therefore need a more powerful pump to achieve a sufficient rate of water circulation.
Other indications to be taken into account are the pump's operating voltage and power rating.
Operating voltage will be a standard mains value (i.e. 230V in the UK), but you still need to establish whether your pump runs on single-phase or three-phase electricity. The choice here will depend on your existing domestic electricity network. The power rating (P) gives you an idea of energy consumption.
Flow and power are related; for a given flow rate, a more powerful pump will last longer before it shows signs of wear.
Why choose a variable speed pool pump?
A variable speed pump, as the name implies, allows the operating speed to be adjusted and in some cases pre-programmed according to your needs. This determines flow rate.
If your pool is large in volume, it requires substantial filtration and its level of use varies widely, a variable speed pool pump is a good option. The same goes if you continue to use it during the winter.
However, the price difference is hard to justify given the limited savings in energy consumption.
How to assess the quality and reliability of your pool pump?
The price range of pool pumps is wide, the most expensive being the variable speed models.
Keep in mind that your choice will depend heavily on the size and format of your pool... A small above-ground pool won't need as robust a pump as a large inground pool.
For pools that are only in use during a short window of time, a fairly basic model of pump should suffice. On the other hand, if your pump is expected to run all year round to serve a heated pool, you'll need a more reliable, higher-end model.
In any case, choosing a self-priming pump equipped with a pre-filter will give you a longer lifespan.
If you use salt as a disinfectant in your pool (or indeed if it's a salt water pool), check that your pump is compatible with salt water.
Finally, noise level (measured in decibels, dB) can be an important factor when making your choice if your pump is installed near the pool or in an area used for other activities.
Learn more about swimming pool equipment...
To find out more about swimming pool equipment, follow our editors' advice and discover their other guides:
Guide written by:
Patrick, Handyman, Bath, 12 guides
Professional maintenance and electronics training. I don’t ask to use my tools on the weekend. The car, the boat, the house with its electric appliances, the garden and its swimming pool, they all remind me that they need my attention. In the absence of an unlimited budget, I try to expand my areas of expertise. There’s nothing I like quite as much as being in the weekend workshop with my buddies. Everyone benefits from his experience which ends up being more-or-less successful, it must be said. But that’s part of the charm of DIY, helping each other and realizing a project in a pleasant way. So, if I can help you, it would be a pleasure.