What the R number on copper tube means, which temper comes in coils or straight lengths, how each is bent and where each is used.
What the R number means
Copper tube for water, heating and gas pipework is made to BS EN 1057. The R number is the temper: how hard and how strong the copper is. It is the minimum tensile strength in newtons per square millimetre, so the higher the number, the stronger and harder the tube.
- R220: annealed (soft), supplied in coils.
- R250: half hard, supplied in straight lengths.
- R290: hard (hard drawn), supplied in straight lengths.
The temper says nothing about the wall thickness. That is a separate choice, so a full order reads EN 1057 – R250 – 15 × 0.7 mm. Straight tube is stamped with its size, EN 1057, its temper, the maker and the date, so read the stamp rather than guess.
R220: soft coils
The small soft coils, 6, 8 and 10 mm, are microbore: run from a manifold to each radiator, behind dry lining or under a suspended floor. Soft coil is also the makers' choice where copper is laid in the ground or buried in a screed, because long lengths avoid buried joints. In the ground it is the thicker-walled 15 or 22 mm coil, and where the soil or screed could attack copper, makers advise factory plastic-coated tube.
Soft tube bends by hand or in a bending machine. Tube from a coil can be out of round, so re-round the end before you make a joint. The Copper Development Association (CDA) advises against a non-manipulative (type A) compression fitting on soft tube over 12 mm unless the tube has an internal support, and calls for the manipulative type underground.
R250: half-hard straights
Half-hard tube, in 3 m or 6 m lengths, is the general-purpose tube for hot and cold water, central heating and gas above ground. It is rigid enough to run straight between clips, yet it still bends cold:
- an internal bending spring for 12, 15 and 22 mm, or an external spring up to 10 mm, for easy bends pulled round the knee;
- a bending machine for tighter bends, and for 28 mm and larger.
Springs stop at 22 mm. A spring must also fit the bore snugly, and the bore depends on the wall: about 13.6 mm for 15 × 0.7 mm tube but 13 mm for 15 × 1.0 mm.
R290: hard
Hard tube is mainly found in the larger sizes: depending on the maker and the wall series, sizes from 35 or 54 mm upwards are hard. Makers state it is not suitable for bending as supplied, so changes of direction are made with fittings.
Wall thickness
Common sizes come in two walls. The standard series (formerly Table X) is 15 × 0.7, 22 × 0.9 and 28 × 0.9 mm. The thicker series (formerly Table Y) is 15 × 1.0, 22 × 1.2 and 28 × 1.2 mm. It takes more pressure and more external load, which is why the CDA specifies it underground. Microbore walls are thinner again, for example 8 × 0.6 and 10 × 0.7 mm.
Heat changes the temper
Heat softens copper. Half-hard tube is annealed for a difficult bend by taking it to a dull red heat, about 600 °C. For the same reason the CDA says half-hard or hard tube that has been softened by brazing must be rated as annealed tube when its working pressure is calculated.