22mm Copper Pipe: When You Need It, How to Work With It, and What It Costs

Your plumber runs the main heating loop in 22mm copper, tees off in 15mm to each radiator, and the system works. Your builder's labourer runs the entire heating circuit in 15mm because it's cheaper and easier to bend. Three months later, the upstairs radiators barely get warm while the downstairs ones are scalding. The fix involves ripping out concealed pipework, replastering, and redecorating. The cost of the 15mm pipe "saving" was about £40. The cost of the repair runs into thousands.

What it is and what it's for

22mm copper pipe is the workhorse size for domestic heating and hot water supply. It carries the main flow and return from your boiler to the point where branches split off to individual radiators, and it's the correct size for higher-flow applications like feeding a bath with a gravity-fed hot water system or running supply to an underfloor heating manifold.

The "22mm" refers to the outer diameter. The wall thickness on standard domestic pipe is 0.9mm, giving an internal bore of 20.2mm. That bore size is what determines flow capacity: 22mm copper can carry approximately 22kW of heat at a flow velocity of 1.5 metres per second with an 11°C temperature difference between flow and return. For comparison, 15mm pipe maxes out at roughly 10kW under the same conditions. That difference is why your heating system needs both sizes, and why getting the wrong one in the wrong place causes real problems.

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All copper pipe sold for UK plumbing must conform to BS EN 1057 (the European standard that replaced the older BS 2871). The grade you'll see in shops is R250 (half-hard), which comes in straight 3m lengths. R220 (soft, annealed) is available in coils for longer runs without joints but is less common in domestic work. R290 (hard-drawn) is rigid and primarily used in industrial applications. For an extension or renovation, R250 straight lengths are what you're buying.

WRAS (Water Regulations Approval Scheme) approval confirms the pipe is safe for potable water contact. Every reputable UK brand carries it.

When to use 22mm vs 15mm

This is the decision that matters. 22mm pipe costs roughly twice as much as 15mm, it's harder to bend, and fittings are more expensive. You don't use it everywhere. You use it where flow rate demands it.

The practical rule for central heating is simple: 22mm for the main trunk from the boiler, tee off in 15mm to individual radiators. Every plumber follows this. The forums are full of heating systems that don't work properly because someone ran 15mm throughout to save money.

One thing to be aware of: larger pipe means more water volume sitting in the pipe between your boiler and the tap. A 22mm pipe holds 314ml per metre compared to 145ml per metre for 15mm. That's more than double the volume of water that has to heat up before hot water reaches the outlet. For long runs to a distant bathroom, this means a longer wait for hot water. Use 22mm where flow demands it, not "just in case."

Types, sizes, and specifications

The technical data for 22mm copper pipe is straightforward, but it's worth having in one place when you're checking what your plumber has ordered or specifying materials for a quote.

Parameter	Value
Outer diameter	22.0mm
Wall thickness	0.9mm
Internal bore	20.2mm
Volume per metre	314ml
Weight per 3m length	~1.7kg
Standard grade	R250 (half-hard)
Governing standard	BS EN 1057
Minimum bend radius	88mm (4 x outer diameter)
Horizontal clip spacing	1.2m max
Vertical clip spacing	1.8m max
Max heat capacity (1.5 m/s, 11°C delta T)	~22kW
Typical lifespan	25-50 years (installation-dependent)

How to work with it

22mm copper is heavier and stiffer than 15mm, which changes how you handle it. The techniques are not difficult, but they're different enough that experience with 15mm doesn't fully prepare you.

Cutting

Use a pipe cutter, not a hacksaw. A hacksaw leaves burrs and an uneven edge that prevents clean fitting of olives and solder joints. A pipe cutter for 22mm costs around £8 – £15 and produces a clean, square cut every time. After cutting, deburr the inside edge with the reamer built into the cutter (the small triangular blade that folds out). Burrs left inside the pipe restrict flow and can damage the O-ring seal in push-fit fittings.

Score marks from a misaimed pipe cutter create weak points. If you score the pipe surface accidentally, cut back to undamaged pipe. Don't leave score marks in the final installation.

Bending

This is where 22mm differs most from 15mm. Bending springs work on 15mm pipe with reasonable effort. On 22mm, they're impractical. Forum after forum reports the same experience: modern thin-walled 22mm pipe splits or bulges under spring pressure, and the physical effort required is extreme.

The correct tool is a scissor-type hand bending machine (sometimes called a pipe bender). The minimum bend radius for 22mm is 88mm (four times the outer diameter). A machine bender achieves this consistently. Apply even pressure. Jerky movements create ripples on the inside of the bend.

Joining methods

Three options, each with a place.

Compression fittings are the most common choice at 22mm. They use a brass nut, a soft copper or brass olive, and mechanical pressure to create the seal. No heat required, no special tools beyond two spanners. Clean the pipe end, wrap a couple of turns of PTFE tape around the pipe where the olive sits, slide on the nut and olive, push the pipe into the fitting to the marked depth, hand-tighten the nut, then a further three-quarter turn with a spanner. Over-tightening crushes the olive visibly under the nut. If that happens, you need a new olive and sometimes a new fitting.

Solder fittings (capillary joints) create a permanent, lower-profile joint. Two types: end-feed (you apply solder wire to the heated joint) and solder-ring (pre-loaded solder inside the fitting that melts when heated). Solder joints require a gas torch, flux, and clean pipe surfaces. They're stronger than compression and less likely to weep over time, which is why plumbers prefer them for concealed runs behind plasterwork. But they need skill and a naked flame, which isn't appropriate near timber joists or in confined spaces without fire protection.

Push-fit fittings are the quickest to install. Push the pipe in, the internal grab ring and O-ring do the rest. No tools needed. But push-fit fittings on 22mm copper have a specific issue that catches DIYers out.

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Clipping and support

22mm copper must be clipped at 1.2m intervals on horizontal runs and 1.8m on vertical runs. Unsupported pipe sags over time, creating low points where air locks form in heating systems. It also creaks and ticks as the pipe expands and contracts with temperature changes. Use plastic pipe clips with a wall plug, not cable clips or cable ties.

Where pipe passes through masonry, it must be sleeved. Copper in direct contact with masonry corrodes. Forum reports document through-wall corrosion within two years on unsleeved pipe passing through stone or blockwork. Sleeve the pipe with a short section of plastic pipe or purpose-made pipe sleeve, leaving a small gap for thermal expansion.

Pressure testing

Before any pipework is concealed behind plaster, boarded into floors, or buried in screed, the system must be pressure-tested. This is a mandatory NHBC hold point and a building control inspection item. The system is pressurised to 1.5 times the working pressure and held for a minimum of one hour. Any drop indicates a leak. Flush the system thoroughly after soldering to remove flux residue, which causes pinhole corrosion if left inside the pipe.

How much do you need

Quantity depends entirely on your layout, but there are rules of thumb for a typical extension.

A single-storey rear kitchen extension adding 4-6 radiators to the existing heating system typically requires 12-20 metres of 22mm copper pipe for the main heating flow and return. That's 4-7 lengths at 3m each. The exact quantity depends on the distance from your boiler to the extension, the route the pipe takes (vertical risers, horizontal runs under floors, drops through walls), and how many bends versus elbow fittings your plumber uses.

Add 10% for cuts and waste. Pipe that's been cut too short is scrap.

For the hot water supply to a new kitchen, the run from the hot water cylinder or combi boiler to the kitchen sink is usually 15mm (sufficient for a single tap). 22mm is only needed for the hot water supply if the run feeds multiple outlets or a high-flow bath.

Cost and where to buy

22mm copper pipe has increased substantially in price over recent years, driven by global copper commodity prices. Current 2026 retail prices across major UK merchants are consistent:

For a typical extension needing 5-6 lengths, you're looking at £140 – £170 for the 22mm pipe alone. The Screwfix 10-pack (£269) only saves money if you buy all ten lengths. You save about £11 over buying ten singles individually, roughly £1 per length. Not worth it unless you genuinely need the full pack.

Wednesbury (a subsidiary of Mueller Industries, manufactured in Bilston, West Midlands) is the dominant brand across all major UK retailers. Yorkshire is the sister brand under the same parent company. Both carry BSI Kitemark, WRAS approval, and a 25-year guarantee. Cubralco is an alternative brand found at specialist online merchants. All three conform to BS EN 1057. There's no meaningful quality difference between them at this price point.

Alternatives

Push-fit plastic pipe (such as Hep2O or JG Speedfit) in 22mm is the main alternative. It's lighter, easier to cut, bends around gentle curves without fittings, and doesn't require soldering. It's also cheaper per metre.

But the trade-offs are real. Push-fit pipe uses internal inserts (stiffeners) that reduce the actual internal bore at every joint, partially negating the flow advantage of using 22mm in the first place. Plastic pipe has a higher expansion rate than copper, needing more allowance for thermal movement on long runs. And many plumbers and building inspectors prefer copper for its proven track record, especially for concealed runs that can't be accessed later.

The practical compromise used on most UK extensions: copper for visible runs, complex junctions, and anywhere near heat sources (behind boilers, near flues). Plastic push-fit for long concealed runs under floors where the ease of routing through joists outweighs the other factors.

28mm copper pipe is the next size up, used for larger commercial or multi-zone residential systems. If your plumber specifies 28mm for a domestic extension, question it. The only common domestic application for 28mm is the main supply on a very large property with multiple heating zones.

Common mistakes

Using 15mm throughout a heating system. Already covered in the opening, but it bears repeating: 15mm pipe cannot carry enough flow for more than about three radiators on a single branch. Systems plumbed entirely in 15mm have cold spots, slow warm-up times, and pump noise from water being forced through undersized pipe at excessive velocity.

Over-tightening compression fittings. Three-quarters of a turn past hand-tight is the standard. A full turn or more crushes the olive and creates a leak path. If you see the olive deforming below the nut, stop. Remove it, fit a new olive with fresh PTFE, and try again with less force.

Leaving flux inside the pipe after soldering. Flux is mildly acidic. Left inside a copper pipe, it attacks the internal wall and causes pinhole leaks that may not appear for months. Always flush the system thoroughly after all solder joints are complete, before the system is filled and pressurised for testing.

Not sleeving pipe through masonry. Copper reacts with alkaline mortar and certain stone types. Unsleeved pipe through blockwork or stone develops green corrosion and eventually fails. The fix requires breaking out the masonry to access and replace the pipe. Use a plastic sleeve wherever pipe passes through any wall, floor, or ceiling.

Confusing imperial 3/4 inch pipe with metric 22mm. On older properties, existing copper pipe may be 3/4 inch imperial (19.05mm OD). A compression fitting designed for 22mm metric will feel loose on imperial pipe. The joint may appear to seal under pressure test but weep slowly once in service. Measure the pipe with digital callipers if there's any doubt. The 3mm difference between 19.05mm and 22mm is visible if you know to look for it.

Where you'll need this

• First-fix plumbing - main heating flow and return runs from existing system to new extension; hot water supply runs where 22mm is specified
• Plumbing layout planning - pipe sizing decisions and route planning for heating circuits and water supply

22mm copper pipe appears during the first-fix phase of any extension or renovation that involves central heating or hot water plumbing. It's a material your plumber will order as a matter of course, but understanding why it's specified (and where 15mm would be wrong) gives you the knowledge to check that the right pipe is going in the right places before it disappears behind plaster.