Incoming main & Pressurised HW cylinders

[Akirakun]

1. I'm putting in a new unvented CH system in a biggish four-storey Victorian terraced house. At present there is very little water pressure and looking in the basement I've found part old lead pipe coming onto a short length of 15mm pipe than back onto lead before going onto copper... no wonder perhaps. When replacing it is there a specific maximum bore that one has to use (25mm polypipe?) or could I go larger?

2. In order to run sufficent HW for three bathrooms would it be better to have 2 pressure HW cyls - 1 for the main bathroom, 1 for the others - and does it matter where these go (e.g in the basement) or will they perform better if gravity is involved?

 

[croydoncorgi]

If there's poor pressure on NO flow, there's not a lot of point going much further with changes to the service pipe. OTOH, if there's good pressure at no flow and it drops rapidly as soon as you open a tap - then it needs replacing with a bigger pipe. 25mm MDPE is usually adequate for most purposes, taking account of supply pressure, length of pipe and max demand in the house. Do the sums for pressure loss to make sure.

I'd have though two cylinders is a bit over the top, unless you're short of space. and why split the service as you suggest? One big cylinder with fast recovery (if necessary something like an MHS Gemini) should be cheaper than two smaller ones, plus duplicated PRVs, zone valves, etc.

 

[ChrisR]

Call your "Water Provider", who will give you a good idea of the pressure available in your area. Less than 2 bar and Unvented wouldn't really work well. Add up the flow from your kitchen and outside (ie all mains) taps when they're on together. Less than 20 litres per minute, and you'll need to do something about it.

 

[keego]

25mm should be plenty, when I was putting in new mains on sites we could feed up to 4 houses off a 32mm main.