A pump is a vital part of the ecosystem of your pond, so it’s important you get the right one.
A pump circulates pond water, and by doing so keeps dissolved oxygen at a safe level in your water, and ensures your fish stay healthy.
Constantly moving pond water encourages aeration and provides the water with nutrients, whilst deterring mosquitoes and preventing algae from growing. Filters, fountains, and waterfalls all need the right-sized pumps in order to function.
There are two types of pond pumps (see also ‘Best Pond Air Pump & Aerator‘), and these are submersible and sit at the deepest part of the pond, or non-submersible and are placed above the surface of the water.
There is a wide range of pond pumps that vary in size and power, and it’s important to consider what your pond’s needs are before buying your own pump.
After all, you wouldn’t want to buy a pump for your large, busy pond that isn’t up to the task of maintaining it, nor would you want an overpowered pump for your small waterfall.
But how do you know which size pump you require? There are two important figures you need to look at, and this concerns the flow rate and head.
These two figures tell you the amount of water a pump can circulate, and how capable it is of overcoming any resistance.
Some of the calculations used to determine what size pump is right for you can look a bit complex and daunting, but below we’ll break down these calculations so correctly choosing the right size pump for your water features will be a breeze.
But first, let’s take a closer look at the types of pond water pumps.
Types Of Pond Water Pumps
We now know that there are two types of water pumps, and these are submersible and non-submersible. Both have their advantages and disadvantages, so let’s explore what those are.
Submersible pumps are meant to be totally submerged underwater in the deepest part of the pond.
You can put these pumps in your pond directly, or use a pond vault or skimmer box to do so. Submersible pumps can be as small as 50 gallons per hour (GPH) and as large as 5,000 GPH.
Submersible pumps are simple to install and for smaller ponds that have up to 1,000 gallons of water can be the more economical option. Submersible pumps are also quiet, and are useful for draining your pond (see also ‘How To Drain A Garden Pond‘).
However, if your pond is populated with fish and other aquatic life then you should avoid a submersible pump that doesn’t use oil.
This is because if the pump malfunctions or breaks, oil can leak into the water and harm the fish.
Non-Submersible Pond Pumps
These pumps are not only a reliable option, but more energy-efficient too. You install the non-submersible pond pumps above the pond in a dry location. For larger ponds that are over 1,000 gallons of water, non-submersible pond pumps are more suitable.
However, they are noisier than a submersible pump and a bit harder to install. But once these pumps are installed, they’re even simpler to maintain than a submersible pump.
What’s The Difference Between Pump Head and Flow Rate?
Flow Rate & Head Height
When trying to determine the right size for your pump, you first have to find the right flow rate. Flow rate refers to the volume of water that is moved per unit of time.
Flow rate is either given in GPH or liters per hour (LPH), depending on where you are.
Now that you know the required flow rate, it is time to determine the head height of your setup. The flow rate in your pump will be different depending on the situation, and is determined by the quantity (head height, or simply head).
This is a term used in engineering and refers to how high a pump will lift water above the pond’s surface. When the head increases, the flow rate of the pump will decrease. The higher the water rises, the harder the friction and gravity will resist the flow.
More powerful pumps can provide more of a flow rate at higher amounts of head. Your pump should produce the flow rate you want at your system’s head height.
Total Dynamic Head (TDH) & Friction Head
The overall head height of a pond configuration is known as Total Dynamic Head (TDH). Getting your TDH calculations accurate is quite complex, and there may be many variables.
However, if you’re trying to calculate for a pond in your backyard (see also ‘5 Cover Ideas For Your Backyard Pond‘) it can be pretty easy. Each foot of vertical distance between the pond’s surface and the highest point to where the water is pumped to would be 1 foot of head, and this distance may also be referred to as static head.
TDH calculations can also include friction head and pressure head. Friction head refers to how the size of the pipe and the material of the pipe affects flow resistance.
For backyard ponds, friction head doesn’t have too much of an impact. There are a few simple ways that you can reduce friction head.
When selecting a pump for your pond, you should always use the pipe size recommended by the manufacturer. Smaller pipes can’t hold as much water and so have a lower flow rate.
A narrow pipe diminishes the power of your pump and may even break some setups.
Friction can also be taken into account by adding 1 foot of head for every 10 feet of horizontal piping between the pump and your feature or filter. Every 90-degree turn in the piping also adds 1 foot of head.
Pressure Head & Max Head
Pressure head refers to how devices that operate using pressure resist such pressure.
If your pump is going to be used for a pressurized filter, spray nozzle, or UV clarifier, then you may need to take pressure head into account.
While it’s fairly simple to estimate pressure head, you can get a more precise calculation using the conversion factor 2.31 feet = 1 psi if you know the actual pressure of a device.
Once you’ve calculated the sources of head, you then have to opt for a pump that provides the correct flow rate at that height.
For example, if you require 3,000 GPH at 10 feet of head, a pump that only provides you with a flow rate at 5 feet won’t be powerful enough.
Manufacturers normally provide a list of the flow rates that their pumps are capable of at numerous head heights. This includes the max head height, and this is the furthest distance a pump can lift water.
The flow rate is zero at the max head height, and you can refer to max head heights to compare their strengths.
These basic guidelines are handy for understanding how flow rate and head height can affect your pump, so now let’s take a look at how you can apply them to your pond setup.
Pump Size Guide For Fountains, Waterfalls and Features
How big your pump is will have a direct impact on how your waterfalls or fountains will look. To keep it simple, we’ll just talk about setups that connect the pump to the water feature.
But if other components are included (for example, additional filters), these will need to be taken into account too.
When choosing a fountain pump, the strength of the pump will determine how high the water rises and how powerfully it does so.
So to work out the required flow rate, you need to measure the diameter of the outlet of the fountain. You need to add 100 GPH to your flow rate for every inch.
You then need to work out your fountain’s head height by measuring the vertical distance from the outlet, to where the pump rests.
If your pump’s maximum head height and this distance is the same, the fountain will only produce a trickle of water.
A pump that has a maximum head height that’s about 1.5 times more than this distance can give you a steady stream of water to the head of the fountain.
So if your fountain has a head height of 22 inches and the outlet diameter is 3 inches, you’ll need a pump that gives you at least 300 GPH and has a maximum head height of around 33 to 35 inches.
When looking for a waterfall pump, it’s a similar process to the one above, with a few exceptions.
If you want to find out the head height, measure the vertical distance from the water’s surface to the tip of the waterfall. Don’t forget to add 1 foot of head for every 10 feet of pipe that connects the pump to the waterfall.
You then need to measure the width of the waterfall where the water will cascade.
For a decent flow, go for a pump that provides a flow rate of 150 GPH for every inch of the width. For a softer flow, tweak this figure to 100 GPH, and for a stronger flow, adjust it to 200 GPH per inch.
So if your waterfall is 20 inches wide, you’ll require a flow rate of 3,000 GPH for a decent flow.
If the distance between your waterfall and the pond’s surface is 6 feet and is connected by 20 feet of hose, your pump has to provide that 3,000 GPH at 8 feet of head height.
Pump Size Guide For Fish Ponds
When trying to determine the right size pump for water circulation, the most vital things to consider are the pond’s volume and how many fish are in there.
If your pond is densely populated, your pump needs to be able to circulate the whole volume of the pond hourly.
So if your pond is 1,200 gallons, your pump should be able to provide a flow rate of 1,200 GPH at the head height of the outlet.
If your pond has a lower population (or doesn’t have any fish), you may only need a pump that can shift half the volume of your pond.
You can estimate the volume of ponds in gallons by multiplying the length of your pond by the width and the depth. This may be harder to do if your pond has an unusual shape, but if this is the case you can multiply the longest, widest, and deepest parts.
While it is ideal to get this as accurate as possible, if your calculations are over by a bit, there is no need to worry.
If there isn’t enough water circulation in your pond, it can harm the ecosystem, so overestimating the volume is better than underestimating it.
Flow rate is also as crucial for pumps that power water filters. If the flow is on the slow side, the filter will be unable to keep up with the pond’s cleaning needs and the quality of the water will decrease.
On the other hand, if the flow is too rapid, the biological filters and UV clarifiers won’t be able to keep up and will be unable to process the pond water effectively.
So how do you strike the perfect balance? Go for a pump that is close to the maximum suggested flow rate of your filter, without exceeding it.
Your filter may also increase the pressure head to your system, and most pressurized filters give you an additional 3-5 feet of head.
Some models can reach 10 feet, and this is normally stated in the user manual. Meanwhile, UV clarifiers give you an extra 1-2 feet.
It is crucial to regularly clean your filter. When filters become clogged, or are not cleaned regularly, it is harder for water to press through them and this increases the pressure.
You may even decide that it is easier to have different pumps for your water features and filters, and this might be for a couple of reasons. Filters need to be running 24/7, but you can turn off a water feature whenever you want.
Plus, a lot of filters are unable to handle the flow rates needed to run a fountain or a waterfall.
Opting for different pumps not only gives you greater flexibility, but ensures optimum performance for your filters and water features, and helps you save on energy bills.
Having a pump for your pond is crucial to keeping your water clean, especially if your pond is populated with fish and other aquatic wildlife.
We know that figuring out the right size pump can be a bit daunting, but we hope our guide has told you everything you need to know!