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Shower Pump Calculator — Pressure, Type & Sizing
Calculate the correct shower pump type and bar rating based on gravity head, required outlet pressure, pipe restriction and shower type.
Vertical distance: tank base to shower outlet
≈1.0 bar minimum for a decent shower, 1.5 for good flow (a 0.5 bar floor is applied)
Total pipe run from pump to shower
Each elbow adds restriction
Each tee adds restriction
Required for mixer showers — boosts both supplies equally
Price for the pump unit
0.03 typical for copper pipe
Each elbow = 0.6m equivalent straight pipe
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How We Calculate This
This calculator determines the correct pump type and bar rating based on your gravity head, required outlet pressure, pipe configuration and shower type.
The formula
Gravity pressure (bar) = Head (mm) ÷ 10,000
Pressure deficit = Required bar − Gravity pressure
Pump rating = Pressure deficit + Pipe restriction losses
Pump bar is sized as the target outlet pressure minus the existing gravity baseline (the standard installer rule of thumb — a booster pump substitutes for the weak gravity feed). For 3000mm gravity head (0.3 bar) with 1.5 bar required: deficit = 1.2 bar. Adding a small indicative pipe-friction loss (roughly 0.0125 bar per metre of 15mm copper at ~10 L/min) keeps the pump need close to 1.2–1.3 bar → select a 1.5 bar pump. Always confirm the final model against the pump datasheet.
Pump type selection
- Positive head: ≥600mm between the tank base and the highest point after the pump
- Negative head (universal): less than 600mm head, or the shower is at/above tank level (e.g. loft conversions); also the safe choice when head is borderline
- Twin impeller: boosts both hot & cold — essential for mixer showers
Frequently Asked Questions
Gravity head is the vertical distance from the bottom of your cold water storage tank to the shower outlet. Measure from the base of the tank in the loft to the shower head position. Every 1 metre of head provides approximately 0.1 bar of water pressure. A typical UK loft tank gives 3-5m head (0.3-0.5 bar) to a first-floor shower, which is usually insufficient for a good shower experience.
A positive head pump activates when water flows past it by gravity — it needs at least 600mm of gravity head between the tank and the pump inlet. A negative head pump has a built-in pressure switch and can pull water up to it, making it suitable when the shower is at or above the tank level (e.g. loft conversions). Universal pumps work in both situations and are the safest choice when head is borderline.
A twin impeller pump boosts both hot and cold water supplies, which is essential for mixer showers (both thermostatic and manual). A single impeller only boosts one supply. Twin impeller pumps are recommended in almost all situations as they maintain balanced pressure across both supplies, giving more consistent temperature control.
For a standard mixer shower, a 1.5 bar pump is usually sufficient. For rain/drencher heads (200mm+), use at least 2.0 bar (2.5+ bar for 300-400mm heads). For multi-head systems with body jets, use 2.5-3.0 bar. Higher bar pumps are noisier and more expensive, so do not over-specify. Common UK brands include Stuart Turner (Monsoon), Salamander and Grundfos, all available in 1.5, 2.0 and 3.0 bar ratings (Salamander's own selector recommends 1.5 bar for a single mixer, 2.0 bar for a larger/rain head and 3.0 bar for multiple bathrooms or body jets).
No. You must NOT connect a shower pump to a combination boiler or an unvented (pressurised) hot water system. Pumps are only designed for use with gravity-fed (vented) hot water systems with a cold water storage tank in the loft and a hot water cylinder. Using a pump with a combi or unvented system can cause dangerous over-pressurisation and will void the pump warranty.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.