What size supply do I have to my meter?

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Hi all,

I'm in the process of needing to upgrade the hot water system in my house. I have a 15mm feed rising in the house, about 24l/min of flow and about 4.5 bar of pressure with the taps running inside. There's currently a small vented cylinder to feed three bathrooms so there's about 10 minutes of total shower time before the hot is exhausted.

So far I have seen four plumbers who have recommended completely different solutions, but the clearest contradiction is that two have told me to upgrade the main, and two have told me to get an accumulator. Of the two that told me to upgrade the main both looked at my water meter, one told me I had 15mm from the main and needed to upgrade the whole feed and one told me I will have 25mm coming in and only need to upgrade the bit that goes from the street to the house.

Thames Water can't tell me what the pipe size is to the meter (they told me to ask a plumber, which is where the whole problem started!), and the meter itself is a plastic affair that fills the entire hole so I can't see the incoming pipe at all. Is there any way that I can find out what I'm working with? I'm completely stumped and don't have the confidence to go forward with any approach at the moment!
 
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There seems to be a lot of conflicting information in your posting.

I cannot believe that you have a flow rate of 24li/min whilst leaving 4.5 bar pressure in the supply pipe!
 
Sorry, should have been clearer, I was trying to give a bit of context. The supply was measured at 24li/min with nothing else running. I measured it myself from the same outside tap with all the taps inside turned on and had about 4.3 bar with everything running and about 5 with nothing running.

Interestingly, whilst walking to the shops just now I spotted two Thames Water technicians working on another house and asked them. They said they were sure it would be 25mm to the meter.
 
Sorry, should have been clearer, I was trying to give a bit of context. The supply was measured at 24li/min with nothing else running. I measured it myself from the same outside tap with all the taps inside turned on and had about 4.3 bar with everything running and about 5 with nothing running.

Interestingly, whilst walking to the shops just now I spotted two Thames Water technicians working on another house and asked them. They said they were sure it would be 25mm to the meter.

Have another go....none of that makes any sense. With 5 Bar static and a even a 15mm feed you should get a much higher flowrate so look at problems with your stopcocks/taps. Be aware that most outside taps have plastic non return valves and it's common to find them damaged from frost resulting in excessive restriction.

I've got 5 Bar static with a 15m run of 60 year old 1/2" copper feed....it's perfectly adequate. Really you need a plumber that understands pressure and flowrates to do some proper testing but they're hard to find.
 
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Okay, genuinely appreciate the feedback. I'm certainly not claiming to know what I'm talking about, but I do know when I get conflicting information that something isn't right. If anything it reassures me that no-one I've spoken to so far is making much sense. To make sure I wasn't being an idiot I just re-ran my pressure tests.

With nothing turned on:
https://dl.dropboxusercontent.com/u/2512/plumbing/IMG_4258.jpg

With two downstairs taps running and the downstairs toilet refilling (so hopefully the cold tank should be drawing too):
https://dl.dropboxusercontent.com/u/2512/plumbing/IMG_4257.jpg

What we're saying is that I should be getting a lot more than 24li/min out of even a 15mm main at those kind of pressures?
 
If you are achieving those static and dynamic pressures and associated flow rates then you mains would not need to be upgraded, if it's a larger Unvented you are considering. In fact your UHW control set will maintain that pressure at around 3 > 3.5bar dynamic
 
How old is the house?

I repair water supply pipes and the most common ones are 1/2 lead, 20mm black alkathene and 15mm copper.
 
The original house is 1930s, but has been extended a few times. The main is lead coming into the house, which I'd like to get rid of, but not sure what's under the road.
 
It is very simple what you need to do to properly measure the dynamic flow rate that you are getting.

Connect your pressure gauge where it will measure the pressure in the pipework.

Then run some cold taps which are supplied from the mains and set the flow rate until the pressure falls to 1.0 bar.

Measure the flow rate from each tap and add the individual flow rates together.

That will give you the dynamic flow rate @1.0 bar which is in effect the "useful" flow rate which still leaves a pressure in the pipework which would operate a shower, combi boiler or unvented cylinder.

Depending on what outlets you have and how many you expect to use at the same time, a minimum of 22 li/min @1.0 bar would often give good results.

Tony
 

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