Shower Booster Pumps benefits and applications

Learn how shower booster pumps work, which one is right for your customer and application, and the benefits of increased pressure and comfort.

When your customers experience low water pressure...a shower booster pump can greatly increase both their water pressure and comfort. We define pressure up to 1 bar as low pressure and pressures from 1.5 to 3 bars as medium pressure which are suitable for a shower. Pressure over 3.0 bar is considered to be high pressure and sufficient for more than one shower or boosting a whole house. But first you must determine if the system is:

Pressurised with an unvented hot water cylinder
Pressurised with a combi boiler
Or open using a cold-water tank

Pressurised systems use mains pressure. You cannot use booster pumps on the outlet from these kind of systems as it is not legal to boost directly from mains in the UK.

In a vented system, water is supplied from the mains to a cold-water tank which is typically placed in the attic at the top of a building. Here the pressure depends on gravity or the vertical distance from the surface water in the tank to an outlet.
This means that tapping points will experience different pressure levels depending on where they are placed in the building. In these instances, you can greatly benefit from a shower booster pump.

Grundfos shower booster pumps come in two main types: the single impeller booster and the twin impeller booster.
The single impeller pump can boost either hot or cold water in a toilet or an en-suite sink  for instance.
Pumps with twin impellers can boost both hot and cold water which makes them ideal for one or more showers. When it comes to sizing, the compact str2-model is ideal if you only need to boost one bathroom, whereas the larger brass amazon model can boost entire homes with multiple bathrooms. "
The SSR2 is available in a 2-bar version while the STR2 features both 1.5- and 2-bar versions. The premium brass Amazon provides 2 and 3 bars in the single impeller version and the Amazon twin version covers the range from 1.5 up to 4 bars.

Now let's look at the difference between positive and negative [universal] head. The shower pumps we have shown so far all need a positive head. This means that the highest point of pipework or outlet must be below the cold-water storage tank by at least 250 mm. This is because a positive head pump works based on a natural flow of 0.5 litres per minute.

But what if you need to to put a bathroom in the attic?
This type of installation means that the water outlet or highest point of pipework would be above the cold-water storage tank. Here you would require a negative head [universal] shower pump, as it activates based on pressure drops. Grundfos shower pumps are available in a version with pressure switches and vessels which make them perfect for dealing with negative head [universal]. We call this feature universal as it can handle both positive and negative head –– it is available on all our models.

Now let’s dive into some applications.

First up we are boosting a single shower. As the pump has a positive head, and we are boosting both hot and cold water simultaneously, we will typically use either the STR2 or the Amazon twin version.

Next, we are again boosting a single shower that is above the cold-water storage tank. This requires a negative (universal) head shower pump –– either an STR2 or an Amazon.

If we were to boost only cold or hot water to a tap or a toilet in a positive head condition, we would use the SSR2 or the Amazon single version. Whereas if the outlet was above the cold-water storage tank, you would require a negative head shower pump, either the STR2 or Amazon universal.

When you need to boost both hot and cold water to all the appliances and tapping points throughout an entire house, you will need to use and Amazon 3 or 4 bar shower pump. And to do the same when in a negative head condition, you must use the Amazon universal twin version. For boosting a combi boiler, you can use the SSR2.

Now let’s sum up with a few basic requirements:
- The booster pumps must be at a minimum of 1 meter below the inlet.
- Hot water temperatures must not exceed 60°C
- And finally, the capacity of the cold-water tank should be at least 50 gallons or 227 liters
- For most applications we recommend the use of Surrey or York flanges.
- Air bubbles in the water tend to rise to the top of the hot water cylinder.
- Surrey and York flanges work by extracting non-aerated water from deeper within the cylinder while the air bubbles exit up and out of the system via the expansion pipe.
- Supplying pumps with air-free water will greatly prolong their lifetime.
And whatever shower booster pump you choose you can rely on all being 3 stage tested, WRAS compliant and assembled and tested in the UK.

Course overview

Modules: 1
Completion time
Completion time: 10 minutes
Difficulty level
Difficulty level: Basic