If you’re after a shower pump then you may be wondering where to start, which is probably what brought you here! But you’ve done well by coming here, as you can’t just jump straight in and expect any old shower pump to work. Shower pumps can be broken down into two main categories: positive head and negative head pumps; and then a further two categories – twin or single impeller. The type that you will need depends upon the layout of your water system. So here’s a quick breakdown to answer that burning question – which type of shower pump do I need?
Positive head shower pump
This type of pump needs a minimum head of at least 3ft 3ins (990mm) between the base of the cistern and the shower head. This is because it relies on a gravity feed of water to kick start the impellers and start pumping hot and cold water. This type of shower pump ‘pushes’ the feed of water to the shower.
Negative head shower pump
These are for situations where the shower pump is going to be sited either above or at the same level as the cold water tank and literally ‘sucks’ the water from the tanks to operate the shower.
Single impeller shower pump
This can only pump one water supply: either hot or cold but hot water in most installations. Its single blade drives the water to the shower mixer and it is generally sited between the mixer valve and the head. Older pumps tended to be single impellers and negative head and very often were installed in the loft leading to problems with water freezing in the winter.
Twin impeller shower pump
This is the more common type of pump in use today. Each impeller (like a tiny propeller) is fed by either the cold or the hot water supply and it delivers both hot and cold to the mixer at an equal flow.
This type of pump should be sited, ideally, in the airing cupboard to reduce noise. The pump should be installed within 13ft (4 metres) of the hot water cylinder and should be at least 1ft (300mm) below the cold water tank.
The decision on positive or negative head pumps is fairly straightforward and is entirely dependent on the head (or lack of it) between you cistern and your shower rose.
Single or Twin Impeller?
But what about whether it should be a single or twin impeller shower pump? If you have a fairly balanced supply – commonly in areas where cold water pressure is not too high, for instance for those who live in houses at the top of a hill – then you could install a single impeller pump on the hot water supply. This will still achieve a good mix of hot and cold water at the shower head.
However, if your supply isn’t so well balanced – and this will be the case for most houses in urban areas where mains pressure cold water enters the property at between 4.0 and 5.0 bar – then you’ll need a twin impeller shower pump to balance the supply to the shower. Otherwise, your hot water could be overwhelmed by the amount of cold and you could have trouble getting a comfortable temperature from the shower.
Centrifugal or Regenerative?
There are two other categories that your shower pump will fall into that you’ll need to consider: centrifugal or regenerative. In a centrifugal pump, the most common type, water is moved in and out by centrifugal force. The direction of the flow out is at right angles to the direction of the flow in. When the pump is activated, water flows in onto the impellers and these push the water out at high speed.
In a regenerative pump, the flow in and the flow out go in the same direction as the axis of rotation of the impeller. Water is propelled around the casing surrounding the impeller blades and the energy created is used to draw more water into the pump.
Centrifugal pumps are generally quieter and more efficient while regenerative shower pumps are cheaper and easier to install.
If you’re planning to put your pump up in the loft or otherwise above the hot water cylinder, then a regenerative pump may well be a better solution for you as these types are less likely to be affected by the air that can become trapped on top of the water in the hot cylinder. But be aware that these can be noisier than the equivalent centrifugal pump.
So now you know which shower pump you need for your bathroom, here’s where you can buy one.
For more information on shower pumps, here are our other articles worth reading:
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