Mains supply suitable for unvented cylinder?

[PatrickB]

Seen some good advice on similar topics on this forum so hoping for some advice. New to this so please excuse misused terminology!

Having a new CH and HW system in my house (typical 3-bed semi, one bath, one shower, considering a future loft conversion with additional shower).

Trying to decide between a combi boiler or a boiler + unvented cylinder for the hot water. Would prefer the cylinder but concerned about the mains supply.

Current situation is a 15mm pipe coming into the house and a 20mm between house and road. Flow rate measured at the kitchen sink (by installer) is 12litres/minute at 3.2bar. Water pressure on the pipe along the road is 6.1bar.

My installer is adamant that if he changes the rising main pipe to 22mm (without replacing the pipe to the road) that will provide a suitable feed to an unvented cylinder. I'm less certain having seen similar topics discussed here.

Any opinons? Any more information I should gather?
Thanks

 

[mickyg]

I'm assuming the 3.2bar is a static pressure as you would expect more than 12l/min otherwise. Your unvented would need more for you to get the best out of it and I wouldn't be surprsied if this meant running a new main from the road as i had to do for my dad. however it would be worth it, unvented is by the far the best system for modern living.

 

[chrishutt]

Current situation is a 15mm pipe coming into the house and a 20mm between house and road.

The 20mm pipe (presumably this is outside diameter) might be lead, probably with a bore of 3/8" (9mm). This size may continue all way to mains in road. This pipe size will seriously restrict the flow rate (which is what you're concerned about - not so much static pressure).

If the pipe is lead, the water company might replace their bit (to your boundary) free of charge (and replace with 25mm poly - 19mm bore), providing you replace your bit. This is what I would recommend you look into.

Your installer doesn't sound as if he knows what he's talking about. Does he have the "unvented ticket" (a certificate to say that he has undergone relevant training and assessment)? If not, don't use him. If yes, I'd still think twice before using him.

 

[Paul Barker]

Many water boards offer a lead for lead replacement deal, if you take out your lead they will take out theirs without charge. You take your 25mm blue pe pipe to the boarder of your land 1 meter deep and leave it rolled up in excess. 25mm to 22mm stop cock in a suitable position inside the house and run the rest of the way in 22mm copper, get your electrician to service bond (gas to electric supply to water supply 10mm) within .6 meters of the stop cock.

 

[ChrisR]

Lead/ free repalcement. Don't bother asking unless your water is pretty soft. Even using the upcoming Euro standard on plumbosolvency (10ppb) instead of the Brit one (50ppb) , most supplies are sufficiently scaled to be safe.
It's 750mm deep, unless it has changed, and on pea shingle if you want to do it right. More often it's trodden onto the ground around 300 in the middle, and just 750 where it shows.
If you try you can get a bigger supply like 32mm connected. It'll only help if you want a lot of flow, but the extra cost of the pipe is minimal. Bigger fittings are exp£ but that's where the losses are greater.

Looking back at the original posting, author should do a search on unvented, megaflo, pressure, etc to read lots more. 12 l/min is hopeless, though it was possibly limited by the kitchen tap itself. The pressure at the k tap static (no flow) is precisely the same as it is in the road.

 

[chrishutt]

In and around Bristol we have hard water, with all lead pipes well scaled internally. Nevertheless Bristol Water (bless them) seem only too happy to carry out lead replacements f.o.c. - I've arranged several, even with 32mm poly. Someone suggested that 32mm supply might attract higher standing charges on a metered supply -worth checking this.

By the way, Bristol Water are asking for tracer wire to be provided alongside buried pipe. This has to be blue plastic coated wire. Perhaps they could use this to check whether you've really dug down 750mm .

 

[Paul Barker]

Fair points. Please note as Chris poiunts out I'm not advocating replacement of lead for what it is, just for wider boar pipes, if your lead isn't squashed and you have sufficient flow this is not your worry.

 

[chrishutt]

But it looks as if 3/8" lead pipe is the problem!

 

[ChrisR]

Have done a few too - you only pay more (rahn Lundin) if your new supply is big, and NOT metered. With a meter all costs are the same.

I recently saw 3/4 lead main which was creased as it hung over a joist, reducing the c/s area hugely. (Probably trodden on too). Like a tuwat I thought I'd straigten it out a bit.
So then I had a 3/4" square pipe and a free fountain. And before you ask - solder.

 

[PatrickB]

Thanks for all the feedback!
To address a few of the points:

Not sure that 3.2bar was the static pressure - that was the reading at the same time as doing the 12l/min measurement on the kitchen tap. I don't think the tap was limiting the flow though because when another tap in the house was turned on the flow rate dropped to below 10l/min.

Installer does sound as though he knows what he's talking about (that's the problem!). He's well certificated and corgi'd.

Have done plenty of reading on unvented cylinders and know anything less than 20l/min isn't even worth considering - the question is whether changing the rising main pipework from 15mm to 22mm will get me there.

Will look into water board lead replacement deals just in case it comes to that - thanks for the pointer.

 

[chrishutt]

Patrick, you seem to be missing a couple of points, if I may put it like that

Firstly, you quote a flow rate of 12 l/min when one tap is open and then 10 l/min when two taps are open. Presumably the 10 l/min is for just one of the taps. You need to measure both and add them together (and even a third and fourth tap - the more the merrier) to get a better idea of flow capacity of your supply pipe.

Secondly, if you have a 3/8" (9mm) bore lead supply pipe, increasing the rising main from 15mm to 22mm isn't going to make that much difference. The major pressure loss occurs through the narrowest long pipe. This is where the problem lies.

 

[kevplumb]

So then I had a 3/4" square pipe and a free fountain. And before you ask - solder.

eeeeeeeeeeeh you cant do that

s against the doobries and that

 

[Agile]

I recently saw 3/4 lead main which was creased as it hung over a joist, reducing the c/s area hugely. (Probably trodden on too). Like a tuwat I thought I'd straigten it out a bit.
quote]

Chris

Can you explain what happened to the lead pipe from a Metallurgy & Materials analysis?

Tony

 

[ChrisR]

Yes mate. It got bent.

 

[kevplumb]