# How do I calculate water volume in CH pipes

#### a1topdog

I'm trying to size an expansion vessel for an unvented cylinder and I need to work out the total water volume of my CH system.

I have got the calculations for most parts of the system but can't find anything on how to calculate the water volume of the pipes.

Can you help out? I need the "per meter" volume for 22mm and 15mm pipes.

Volume of a cylinder is area x length. Or pi x radius(squared) x length.

So, for 22mm pipe, one metre will contain approximately:-

3.142 x .0022 x .0022 x 1 = 0.00000152 cubic metres, or 1.52 litres.

Similarly for 15mm, 0.7litres.

Worth checking my maths.

Thanks Ian - your formula confirms what someone else told me but the radius would be 0.0011 on a 22mm pipe.

0.0011
Nonsense. That's 1.1 millimeters
22mm is the outside diameter, it's 0.9mm thick so the radius is 0.0101m

and for 15mm which is 0.7 for the rigid stuff (or 0.5 for the bendy one)
r = 0.0068

Hope you have the rad volumes - much more than the pipes!

I'm trying to size an expansion vessel for an unvented cylinder and I need to work out the total water volume of my CH system.

For an UNVENTED CYLINDER? If you mean this, it will not be your decision. It's either the manufacturer if it is supplied in a package, or a G3 registered installer.

If you didn't mean it, you don't need to be accurate, just work it out roughly and then add say 50%, or more. You can't have a vessel that's too big. Bigger vessels are less stressed.

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