Negative Head Shower Pumps (Twin Impeller)

You need a negative head pump when the outlet you want to feed, typically the shower head, sits higher than your cold water storage tank, a common situation in loft conversions with an ensuite. Check the vertical relationship: if the shower head is above the top level of the tank, the pump must be capable of drawing water upwards. If the shower sits below or level with the tank you do not need a negative head model.

Twin impeller pumps have two separate impellers so they boost hot and cold supplies independently, maintaining a balanced pressure to mixer showers. That balance reduces sudden temperature swings when another tap runs, giving a steadier showering experience. Choose a twin impeller if you have a mixer valve or want consistent flow from both feeds.

our range splits pumps by boost level: Up To 2.0 bar gives a low-to-medium lift, while Over 2.0 bar provides a larger boost. If you use a standard shower handset or mixer a pump up to 2.0 bar will usually be sufficient; if you have a large rain head, multiple jets, or want a noticeably stronger stream, aim for a model over 2.0 bar. Match the pump to the flow needs of your shower fittings for best results.

The Grundfos STR2 2.0CN is a twin impeller negative head pump rated at 2.0 bar, so it's designed for loft situations where the shower outlet sits above the cold tank and it provides a low-to-medium boost. For a typical loft ensuite with a standard shower handset or mixer valve, it will usually give a reliable, balanced flow. If you plan a high-flow rainhead or multi-jet setup you may need a higher-rated pump.

Look at the pressure or flow requirements on your shower valve and handset; our range's split into up to 2.0 bar and over 2.0 bar helps you match pump output to those specs. if your valve performs well around 1.5–2.0 bar, the STR2 2.0CN is a sensible match; if the fittings list higher pressure needs, choose a pump from the over 2.0 bar group. Matching those numbers keeps temperature stable and avoids poor performance.