Which pipe should I use for hot and cold water?
The material question is largely settled by joints. Copper's advantage is that it can be soldered or press-fitted into a joint that lasts as long as the pipe and is happy at any temperature the system reaches; the cost is skill and time. PEX turns the job into flexible runs with far fewer joints, and manifold systems mean each fixture has its own uninterrupted run, which reduces the number of concealed joints to almost none. The important constraints are specific and easy to miss: plastic pipe must not be used within the distance of the boiler or cylinder that its manufacturer specifies, it needs inserts at every push-fit joint, and it must be kept out of sunlight because UV degrades it. In water areas with aggressive supply chemistry, local plumbers know which material fails, and they are the better authority than any general rule.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Copper | Rigid, dimensionally stable, unaffected by UV and heat, and it can be soldered or pressed. | Needs skill and heat to join, costs more, and pinholes in aggressive water areas. |
| PEX | Flexible, fast to install with fewer joints, and it expands rather than splitting when frozen. | Degrades in sunlight, cannot be used at a boiler outlet or near heat, and rodents chew it. |
| CPVC | Common in North America for hot and cold, solvent-welded, and cheap. | Becomes brittle with age, and it is incompatible with some pipe-thread compounds and sprays. |
| Push-fit fittings on either | Fast, need no tools or heat, and can be used on a wet system. | Bulky, need pipe inserts on plastic, and rely on an O-ring — so they belong where they can be inspected. |
Technique that changes the outcome
- Fit pipe inserts in plastic pipe at every push-fit or compression joint
- Use copper for the first metre or so from a boiler or cylinder, per the appliance instructions
- Support plastic pipe far more frequently than copper; it sags between clips
- Pressure test before closing anything up
What goes wrong
- Plastic pipe exposed to sunlight or run near a flue
- Omitting inserts, which is the classic cause of a joint that weeps months later
- Concealed push-fit joints where they cannot ever be inspected
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other pipe questions
| For | Use |
|---|---|
| Waste and drainage | Solvent-weld or push-fit PVC-u or polypropylene, at the right diameter and fall — and ABS and PVC cements are not interchangeable. |
| Central heating | Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside. |
| Boiler condensate | Plastic, never copper, at a generous diameter with continuous fall — and insulate any external run, because frozen condensate is the classic winter breakdown. |
| Gas | Steel, copper of the right grade, or yellow MDPE underground — and in most jurisdictions only a registered installer may do the work. |
| An underground water supply | Blue MDPE for potable water, in one continuous length at the required depth, with no joints under a building. |
| Compressed air | Copper, steel, stainless or a purpose-rated aluminium or HDPE air system — never PVC, which fails explosively. |
| Irrigation | Low-density polyethylene tubing with barbed fittings for drip lines, and PVC or MDPE for buried mains. |
Common questions
- Which pipe should I use for hot and cold water?
- Copper or PEX for most installations — PEX is faster and more freeze-tolerant, copper is more robust and takes heat without question.
- What should I avoid?
- Plastic pipe exposed to sunlight or run near a flue Omitting inserts, which is the classic cause of a joint that weeps months later Concealed push-fit joints where they cannot ever be inspected
Related pages
- Which pipe should I use for waste and drainage? Solvent-weld or push-fit PVC-u or polypropylene, at the right diameter and fall — and ABS and PVC cements are not interchangeable.
- Which pipe should I use for central heating? Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside.
- Which pipe should I use for a boiler condensate drain? Plastic, never copper, at a generous diameter with continuous fall — and insulate any external run, because frozen condensate is the classic winter breakdown.
- Which pipe is used for gas? Steel, copper of the right grade, or yellow MDPE underground — and in most jurisdictions only a registered installer may do the work.
- Which pipe should I use for a buried water supply? Blue MDPE for potable water, in one continuous length at the required depth, with no joints under a building.
- Which pipe should I use for compressed air? Copper, steel, stainless or a purpose-rated aluminium or HDPE air system — never PVC, which fails explosively.
- Which pipe should I use for irrigation? Low-density polyethylene tubing with barbed fittings for drip lines, and PVC or MDPE for buried mains.
Sources
- Typical range compiled from manufacturer specifications — At One Place