Water pressure / supply pipe / unvented cylinder question

[Trebby]

Hi,
Hope somebody can help me. We live in a tall victorian house. Shower pressure has been poor for some time, and so we had a large plumbing company round who suggested changing our gravity-fed water system for an unvented cylinder. I showed them our incoming supply pipe, which was 15mm, but they said that the flow rate was sufficient that this wouldn't matter.

The cylinder is now fitted and shower pressure is significantly improved, but certainly not like a power shower. This includes when it is the only asset using water. In this circumstance, is upgrading the supply pipe to 22mm going to achieve anything? Or will it simply mean that two people can shower at the same time with the same low pressure?

I've not been able to measure the pressure, but the flow rate is about 12l/min downstairs.

Thanks for any advice.

 

[Trebby]

I should mention that pipe beyond the unvented cylinder to the rest of the house is 15mm.

 

[Madrab]

No unvented manufacturer that I know of recommends the use of a 15mm supply pipe to their hardware, for exactly those reasons. If it must be used then a minimum flow rate is recommended, usually around 20L/Min @ 1.5bar dynamic. If that can't be met then it's not performing to it's best ability and your not getting value for money. You only get out what you put in with UVHW.

Did they actually check the dynamic flow and pressure?

Now it's in though there's not a lot you can do, especially as it has improved the supply. Remedial action like upgrading the supply may work but you need to get the supply checked. Dynamic flow and pressure needs to be know to see if an upgrade will be worth it.

 

[Gasguru]

The pressures and flowrates need measuring...I have an old 1/2 copper service pipe 10m long but a 5 bar street pressure is sufficient that even with every tap in the house open there's still plenty of flow.
Measure first then decide.

 

[Trebby]

Thank you for your reply - that's helpful. I've persuaded Yorkshire Water to come and investigate the 'low' water pressure - so I'm hoping they will do some measurements.
As I recall, pressure and dynamic (?when multiple taps are on) weren't checked. They measured static flow from the kitchen tap and said it was 'plenty'.

What I can't get my head around is whether upgrading the supply will improve water pressure/flow beyond the cylinder.

 

[Madrab]

If you have the dynamic pressure then 15mm can still deliver plenty of flow, albeit more noisily. Therefore 15mm pipe can still be ok as distribution pipework but if the dynamic pressure - more then one outlet open - can't be sustained then you'll never obtain the best performance from 15mm.

Dynamic pressure and flow is the most important thing when it comes to un-vented. Did they sign off the installation (benchmark) and was the fitter qualified?

 

[Trebby]

It was done by a large local company who are definitely G3 registered. They did sign it off..but I don't know that they took flow and pressure measurements after. Are they supposed to?

 

[Madrab]

Well it depends on them I guess, there's no rules that say they should. Depends on how 'professional' a service they deliver IMO. The could look it as - Your HW delivery is now better than it was so you've got what you asked for.

As an unvented installer though I wouldn't recommend one until I knew the dynamic figures could sustain a reasonable level of delivery, to me that's around the 20L/min mark @ a min of 1.5bar dynamic. It seems pointless to me to install a system otherwise, if it was me I'd feel I hadn't got what was reasonably expected TBH.

As with so many UV questions tho, we need to know dynamic supply pressure and flow.

 

[Trebby]

Thanks for the reply - much appreciated. I'll update when I've got the flow and pressure figures.

 

[lostinthelight]

Thanks for the reply - much appreciated. I'll update when I've got the flow and pressure figures.

Thank you for your reply - that's helpful. I've persuaded Yorkshire Water to come and investigate the 'low' water pressure - so I'm hoping they will do some measurements.

I asked welsh water to check my pressure and flow before installing uvc which they did foc

 

[Madrab]

Just remember they'll be testing at their access and not after your supply entering the house, mind also to get dynamic figures as they may only test static pressure and flow unless you're there with outlets open

 

[Trebby]

Thanks for all the advice. They tested flow in the end rather than pressure, and determined that we were getting 10 l/min inside. At the pavement/house stopcock the flow was 81 l/min. Paid the guys a bit of cash and they upgraded the mains supply pipe to 25 mm. Even though the meter and beyond is 15mm things are definitely much better and I think we'll probably leave it as it is. Cheers.