​Coefficient of linear expansion

​How much does a piece of material expand by when heated?

​In every installation, plumbers need to take into consideration the expansion of materials:

when hot water flows through pipes;
when the material is in the sun or in the shade. ​ 

​Plastic guttering expands the most out of all installations.
​ 

Also creaking pipework under floors is due to expansion and contraction.

​Whenever we fit plumbing systems we must make sure we allow for the effects of expansion.

But firstly we need to know how to calculate the expansion of common materials we use.

This is called:
​Coefficient of linear expansion​ 

Length of material x the temperature rise x the coefficient of expansion for that material. ​ 

​Coefficient of expansion for some common plumbing materials

​Coefficient of linear expansion​ 

Length of material x the temperature rise x the coefficient of expansion for that material. ​ 

We can see in the table that plastics have the greatest expansion, and as plumbers we must keep this in mind when designing and installing systems.

​Coefficient of linear expansion​ 

Length of material x the temperature rise x the coefficient of expansion for that material. ​ 

To calculate the amount of expansion is quite easy, take the starting length of the material in millimetres (mm) multiply this by the amount of temperature rise in (⁰c) multiplied by the materials coefficient of expansion (COE)

​Coefficient of linear expansion​ 

Length of material x the temperature rise x the coefficient of expansion for that material. ​ 

So to calculate the COE for a 10 metre plastic gutter system, which when in direct sunlight would warm by 20⁰c, the equation would be:

10,000 (amount of mm in 10 metres) x 20 (⁰c) x 0.00018 (The COE for plastic)

So to calculate the COE for a 10 metre plastic gutter system, which when in direct sunlight would warm by 20⁰c, the equation would be:

10,000 (amount of mm in 10 metres) x 20 (⁰c) x 0.00018 (The COE for plastic)


10000 x 20 x 0.00018 = 36

So the gutter would expand by 36mm

​Try the calculations on the following slides: