Appropriate pipe sizes for shower

ajbaker

Hi.

I am about to fit a built-in/recessed shower valve and am wondering which diameter pipe is most suitable - 15 or 22.

Details:
Combination boiler is around 4-5 metres from the shower on the same floor;
domestic cold supply is all 15mm;
combi to half way to shower is 22mm;
shower is an Aqualisa Aquatique thermostatic valve with 5" rose - so I guess pressure is not the main priority, but volume of water is;
both inlets of the shower are 3/4" BSP;
output of shower is 3/4" BSP;
shower arm from wall to rose is 18mm diameter.

I need to know the diameter of pipe to use for the remaining last half of the distance from boiler to shower for the hot supply. And the diameter to use for the riser from shower outlet to shower arm.

The manual suggests 15mm should be sufficient for boiler to shower, and 22m is best for the riser to the shower arm. I am wondering if there is an advantage using all 22mm or all 15mm.

Thanks in advance.

economiser

The only disadvantage of using 22mm is the hot water will take a few seconds longer to from boiler to shower head because of the larger water content of the pipe.

plumb1_2

Your outlet from your bolier will be 15mm, so pipe it in 15mm, dont use 22mm as you will cause the water to be airated.
On the exposed model they are 15mm inlets, same valve.

ajbaker

plumb1,

You are right, the pipe from the boiler is 15mm but it is joined to the original 22mm pipe very soon after. I really wasnt thinking of replacing any of the existing pipe, but will if I notice problems. Presumably there are no issues going back down to 15mm before the valve? Would you still recommend using 22m for the riser?

To connect the riser to the 18mm shower arm I have two options:
1. use a 22mm to 3/4" BSP male elbow joined to a 3/4" BSP female-18mm compression connector or;
2. use a 22mm elbow with an 18mm olive.

How reliable are 18mm olives in 22mm compression joints. Are they commonly used for recessed pipe work?

plumb1_2

ajbaker wrote:

plumb1,

You are right, the pipe from the boiler is 15mm but it is joined to the original 22mm pipe very soon after. I really wasnt thinking of replacing any of the existing pipe, but will if I notice problems. Presumably there are no issues going back down to 15mm before the valve? Would you still recommend using 22m for the riser?

To connect the riser to the 18mm shower arm I have two options:
1. use a 22mm to 3/4" BSP male elbow joined to a 3/4" BSP female-18mm compression connector or;
2. use a 22mm elbow with an 18mm olive.

How reliable are 18mm olives in 22mm compression joints. Are they commonly used for recessed pipe work?

Thats the problem when people have a boiler swop, the old 22mm should be taken out and replaced with 15mm idealy(but rearly done) Why is my bath tap so slow etc.

Yes i would pipe the riser in 22mm.