Manifold plumbing: layout, pros and cons, and DIY installation

There are two ways to run water around a home. In a tee-branch layout, one pipe passes all the fixtures and each one tees off it. In a manifold layout, every fixture has its own pipe from a shared header — the manifold. A manifold needs more pipe, but it gives steady pressure and lets you isolate any fixture without shutting off the whole house.

What the diagram shows

1 — the cold water manifold, 2 — a valve on each manifold outlet, 3 — a fixture with its own dedicated pipe, 4 — the hot water manifold.

Pros and cons

• Steady pressure. When someone starts the washing machine, the shower does not go colder or weaker: each fixture draws from the manifold rather than from a shared pipe after its neighbour.
• Easy repairs. To replace a mixer or trace a leak, you close one valve on the manifold.
• Fewer joints in the walls. The pipe from the manifold to a fixture runs in one piece.
• Cons: more pipe, more space for the manifold (usually hidden in a cupboard or recess), and a higher cost.

What it consists of

1. The inlet assembly: a valve, a mesh filter and, where needed, a pressure reducing valve and a meter. See “Water pressure reducing valve”.
2. The cold manifold, 3/4" or 1", with one outlet per fixture plus one or two spares.
3. The hot manifold, fed from the water heater or boiler.
4. Outlet valves — ball or stop valves, labelled with the fixture each one feeds.
5. Pipes to the fixtures, usually 16–20 mm. How to size them is explained in “Choosing the pipe diameter”.

Step-by-step installation

1. Draw a plan: where the manifold goes, where each fixture is and how the pipes will run. Count the outlets.
2. Fix the manifolds to the wall or inside a cupboard so the valves stay accessible.
3. Run each pipe to its fixture in one piece, with no joints inside the walls, ideally in a protective sleeve.
4. Label the outlets and pressure-test the system: fill it, raise the pressure and leave it for several hours, checking the gauge and every joint. Only then close up the walls.

Pipes, fittings and valves are in pipes and fittings and valves and fittings. How to weld polypropylene is explained in “Welding polypropylene pipe”.