Which pipe should I use for central heating?
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.
A sealed heating system is designed to become oxygen-depleted: once the small amount of dissolved oxygen in the fill water has reacted, corrosion effectively stops and the system can run for decades. Non-barrier plastic pipe defeats that by allowing oxygen to diffuse continuously through the pipe wall, so corrosion never stops — the result is black magnetite sludge, cold spots at the bottom of radiators, a failing pump and blocked heat exchangers. The barrier layer, usually EVOH or aluminium, is the entire point of heating-grade plastic pipe and it is not a marketing distinction. Add an inhibitor to the system water and fit a magnetic filter, and the corrosion products that do form are captured rather than circulated.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Copper | Impermeable to oxygen, takes any system temperature, and rigid enough to hold its line neatly. | Costs more and takes longer to install. |
| Barrier PEX or PE-RT | An EVOH layer stops oxygen diffusing through the wall, which is what makes it usable in a sealed heating system. | Must be the barrier grade, and it needs inserts and frequent support. |
| Multilayer (PE-AL-PE) pipe | An aluminium core gives a total oxygen barrier and lets the pipe hold a bend like metal. | Needs press or compression fittings and the right tooling. |
| Non-barrier plastic pipe | Cheap, and fine for cold water and irrigation. | Oxygen diffuses straight through it into the heating water, rusting radiators and pump from inside. |
Technique that changes the outcome
- Use only barrier-grade pipe, and check the printing on the pipe itself
- Fit inserts in every plastic joint and support the pipe frequently
- Flush the system and add a corrosion inhibitor after any work
- Fit a magnetic filter on the return before the boiler
What goes wrong
- Non-barrier pipe anywhere in a heating circuit
- Mixing metals badly — an aluminium radiator on an unsuitable inhibitor corrodes quickly
- Skipping the inhibitor after draining the system, which is the commonest cause of sludge
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 |
|---|---|
| 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. |
| 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. |
| 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 central heating?
- Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside.
- What should I avoid?
- Non-barrier pipe anywhere in a heating circuit Mixing metals badly — an aluminium radiator on an unsuitable inhibitor corrodes quickly Skipping the inhibitor after draining the system, which is the commonest cause of sludge
Related pages
- 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.
- 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 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