15mm or 22mm shower plumbing

[Jim Walsh]

Hi guys. I'm just about to install a shower pump, and being both lazy and tight, I devised the most economical way of doing it in terms of time and money. I suspect that the fallout from this will be poor shower performance, but what the hell, the bits are ordered now. Anyway, here's the situation: cold supply from the tank in the loft to the (single) bathroom is run in 15mm pipe. The hot supply from the h/w tank to the bathroom is 22mm, but unlike the cold, this is not a dedicated supply as it feeds the kitchen also. I considered whether to buy a pump with 22mm inlets/outlets or whether to go for a 15mm fitting version. I decided that there would be less plumbing to do if I went for 15mm, since the existing cold could simply be re-routed through the pump and a new (dedicated to shower) hot drawn from the tank in 15mm pipe via a Surrey flange. This set up means that the only new pipework I would have to lay is a new hot from pump to shower (

[Christian McArdle]

It all depends on the length of pipework. For a simple shower in a normal house with standard layout, I suspect 15mm will normally be fine. However, there are circumstances in which 22mm would be better, such as long runs, panel showers etc.

15mm has some advantages too. As well as being easier to install/route/conceal, it means that the hot water becomes available sooner if the pipes are cold.

Christian.