15mm or 22mm water feed

330d

Hi, I am currently in the middle of a house renovation. I have a 250l invented cylinder and a 30kw system boiler.

The water pipes going to the bath tub and shower, is 15mm ok or do they need to be upgraded to 22mm?

grumbler

UNvented

IMO, if your mains pressure is good, 15 is fine. 22 is needed for low-pressure gravity-fed systems.

Davesnave

There again, if you live in a hard water area and don't intend to soften it, building-in some over capacity might not be such a bad idea.....

Jeepers_Creepers

330d, are you going plastic or copper?

I'd be tempted to go 22mm too, tobesure tobesure, and definitely so if 'plastic' as the internal dia's are smaller than copper's.

So 22mm plastic or 15/22mm copper. But leaning towards the 22mm...

NSG666

What is the hot water flow rate like? Is it a single run or does it branch off to other parts of the house?
How long is the run? remember 22mm pipe will also waste more water as you need to run more before it gets hot and then you leave more hot water in the pipe to go cold.

Plastic doesn't suffer from limescale build-up.

Jeepers_Creepers

Damn, he's right...

22mm is only used when it needs to be - ie low pressure 'gravity' systems.

330d, I would personally take the initial output from the unvented in 22mm (unless the inlet is in 15mm, in which case don't bovver), and then tee-off in 15mm to each bathroom as get towards them and as required.

Ditto with combis - make the stopcock-to combi run in 22mm as far as possible, then tee-off 15mm to the house cold and ditto to the combi inlet. It probably doesn't make a huge amount of difference, but it'll make the best of the situation. And if your mains pressure ain't brilliant, it'll help more.

330d

Just to update this, old bath has been removed and the hot water pipe is 22mm so that's good. I thought it was 15mm.

One other question, the shower has a 300mm head along with 4 body jets. Will 15mm be ok for this or does this also need to be 22mm?

grumbler

I can only repeat, 22 is usually needed only for gravity fed systems. And your 22mm pipe to the bath is only from the former hot water cylinder - nothing 'good' unless your new boiler is in the same cupboard where the cylinder was or you are going to run 22mm pipe from the new boiler to this place.

330d

Boiler and cylinder and both next to each other.

grumbler

Sorry, I forgot about the unvented cylinder. Anyway, there's no point in replacing the existing 22mm pipe, but it's unlikely to make any difference compared to 15 as your hot water now is under the mains pressure.

330d

I was thinking of flow. Will 15mm be sufficient to feed the 300mm shower head and also the body jets?