Which pipe to choose for the job

Choosing by the job

No time for the whole page? Go by the job — nine times out of ten the answer is here:

• Concealed water pipework in a flat, budget matters → reinforced PP-R.
• Underfloor heating or manifold runs → PEX, one continuous piece with no joints in the screed.
• Exposed runs and radiator connections → multilayer: it holds a bend and looks straight.
• Boiler room, high temperatures, an install meant to last decades → copper.
• Supply from a well or borehole, buried in ground → HDPE.
• Short connections to a tap or appliance → a flexible hose or corrugated stainless.
• Gas → certified gas connections only (yellow-marked) or steel pipe. A water hose won't do for gas; they're different products.
• An old steel riser you need to tie into → the steel stays; the transition to plastic is made in brass.

Six materials in cross-section

From the outside half of these pipes look identical — white or grey plastic. What tells them apart is the wall:

Comparison at a glance

PP-R — polypropylene

Welded with a cheap iron, joints become monolithic and can be buried in walls. The catch: an overheated joint narrows the bore, and you can't see that from outside. Rigid pipe, every turn is a fitting.

Choose the right class: PN10 is cold water only, PN16 takes cold and warm water up to ~60 °C; for hot water and heating — reinforced PN20/PN25, which also sags far less on long runs.

• Glass-fibre reinforcement sits inside the wall and welds like plain pipe — nothing to strip. It's easier to work with, which is why most domestic jobs use it.
• Aluminium reinforcement has to be stripped, and which tool depends on where the layer sits. Outer reinforcement — foil under a thin skin of polypropylene — is taken off with a shaver, over the full socket depth. Mid-wall reinforcement is faced off the end with a facing tool.
• Aluminium left in the seam is the classic reason a PP-R joint weeps a year later. Some modern deep-layer pipe needs no stripping at all — check the manufacturer's instructions.

Unreinforced pipe expands 0.15 mm per metre per degree, reinforced 0.03–0.05 — three to five times less. That's what makes long hot runs go wavy.

PEX — cross-linked polyethylene

Flexible, comes in coils, turns without fittings — which is why whole floors are piped with it from a manifold, with zero joints inside the screed. Joined with axial (sliding sleeve) or press fittings — both need a dedicated tool; at the manifold each run usually lands on a eurocone compression fitting, where a spanner is enough.

Doesn't like sunlight (UV degrades it) and doesn't hold shape — visible runs look wavy. Its home is inside floors and behind walls, each run one whole piece.

• For heating, buy pipe with an oxygen barrier (an EVOH layer, marked as barrier pipe). Without it oxygen passes through the wall and rusts cast iron, steel and the pump.
• PE-Xa is peroxide-cross-linked: the most flexible of the three, and a kink in it straightens out with a heat gun. PE-Xb and PE-Xc are stiffer — a kink in them can't be repaired, it gets cut out.
• In an axial fitting the pipe itself is the seal: the sleeve slides over it and presses it into the grooves of the spigot, with no rubber rings at all — which is why it's considered the safest choice for burying in screed.

Multilayer — PEX-AL-PEX

An aluminium layer between two polyethylene ones: bends by hand and holds the shape, so it suits visible runs and awkward corners. Joined by press fittings (tool needed, joint can be hidden) or compression fittings (a wrench is enough, but the joint must stay accessible).

The weak spot is careless assembly: an uncalibrated cut edge cuts the o-ring and the joint weeps months later. Calibrate every cut.

The aluminium doubles as an oxygen barrier, so multilayer needs no separate EVOH layer.

Copper

Durable for decades, handles any household temperature, looks good uncovered. Joined by soldering or press fittings; soldering demands skill and means open flame indoors, press demands an expensive tool.

The material and fittings cost the most of anything here. One rule is non-negotiable: copper meets steel only through brass — why, and in what order along the flow.

HDPE — the pipe from a well or borehole

Black pipe with a blue stripe, sold in coils — this is what brings water into a house from a borehole, a well or a street main. Cheap, unbothered by soil, and it survives a light freeze better than rigid pipe.

Joined with compression fittings by spanner or with electrofusion couplers. Underground, the aim is no joints at all: a coil covers the whole run, and every buried joint is a future excavation.

• The blue stripe means potable. Plain black pipe with no stripe is technical grade and isn't for drinking water.
• Cold water only: working temperature is around 40 °C, so HDPE never goes on hot.
• An HDPE compression fitting grips the pipe from outside and a rubber ring does the sealing: the cut must be square and chamfered, and the pipe pushed in to the stop. An internal support sleeve is only needed for thin-walled pipe (SDR 17 and thinner) — stiff PE100 SDR 11 holds the grip on its own.
• Black HDPE is carbon-black stabilised against UV and shrugs off sunlight for years. What actually threatens it above ground is impact and freezing — which is why exposed sections still go into a sleeve.
• PE80 and PE100 are polyethylene grades: PE100 is stronger at the same wall thickness. Pressure rating, SDR and diameter are printed alongside.

Steel, brass and stainless

New water lines are rarely built from threaded steel today, but the housing stock is full of it — so half of all plumbing work is transitions from old steel to new plastic. That's done with brass: nipples, couplings, reducing bushes.

Brass is the connective tissue of the whole system: valves, manifolds, adapters between any two materials above. Brass isn't a pipe material; it's what ties the other materials together.

Flexible corrugated stainless is a material of its own for short runs: tap connections, boiler pipework, gas hook-ups. It bends by hand and takes the heat, but it's expensive and never used for long lines.

What connects to what

Different systems only meet through a thread — there's no direct plastic-to-plastic transition between families:

Hence the buying rule: count not just pipe and fittings, but a transition at every boundary between systems — those are the parts people forget.

Where each material doesn't belong

Field tips

Short rules that save you redoing the job.

Common questions