PLUMBCRATE
What size pipe for a shower: 15mm or 22mm?
Quick answer: most UK showers are fed with 15mm copper or plastic pipe at the shower itself. A 22mm supply is often used for the main run to mixer showers on low-pressure gravity systems, pumped showers and high-flow showers, then reduced to 15mm near the valve. Electric showers take a 15mm cold mains feed. Always check the shower manufacturer's installation instructions for the pipe size, pressure and flow rate it needs.
Pipe size by shower type
- Electric shower: 15mm cold mains supply. It heats its own water, so there is no hot feed.
- Mixer shower on a combi boiler or unvented cylinder: usually 15mm hot and cold at the valve. On longer runs or where several outlets share the supply, 22mm for the main run helps keep flow up.
- Mixer shower on a gravity (tank-fed) system: low pressure means pipe size matters more. A 22mm run from the cylinder and cold tank, reduced to 15mm near the valve, is common.
- Power shower or shower pump: pumps usually call for 22mm feeds from the tank and cylinder. Check the pump instructions; many specify a dedicated feed.
Why 22mm can make a difference
Bigger pipe loses less pressure over distance and carries more water. On a short run to a mains-pressure shower, 15mm is usually fine. On a long run, a gravity system, or where a bath tap may be running at the same time, 22mm for the main pipework helps avoid weak or fluctuating flow. See the UK copper pipe sizes guide for sizes explained.
Steps to plan your shower supply
- Check what type of hot water system you have: combi, unvented cylinder, or gravity-fed cylinder with a cold tank.
- Read the shower or pump manufacturer's instructions for minimum pressure, flow rate and pipe size.
- Measure the run and count the bends. Long runs with many elbows favour 22mm.
- Fit isolating valves on the hot and cold feeds so the shower can be serviced. Full-bore valves such as the 15mm full bore isolating valve keep restriction low.
- Use reducers where you step down from 22mm to 15mm, in end-feed, compression or press-fit water fittings.
Electrical work for an electric shower must comply with UK wiring regulations and is notifiable, so use a qualified electrician.
FAQs
Is 15mm pipe big enough for a shower?
For most electric showers and mains-pressure mixer showers on short runs, yes. On gravity systems, pumped showers or long runs, a 22mm main run is often recommended. Check the manufacturer's instructions.
What size pipe does a shower pump need?
Many shower pumps specify 22mm feeds from the cold tank and hot cylinder. The pump's installation instructions give the exact requirement.
What size pipe for an electric shower?
A 15mm cold mains feed is standard for an electric shower.
Can I reduce 22mm to 15mm for a shower?
Yes. A common layout is a 22mm main run reduced to 15mm close to the shower valve using a reducer.