Low water pressure due 15mm pipe supply?

[Draez]

Hi all

Here's a problem. 3 storey victorian terrace house, water pressure/flow good on ground floor, gets worse the higher you go up (esp cold water), at the top pressure and flow poor, less than half on the ground. The neighbours don't have the same problem. Plumber (friend of a friend) took a look, all valves fully open, Potterton combi boiler with unvented water heater tank (described by plumber as like a cheap megaflow) functioning normally...however, he noticed that the 22mm feed from the main (and the 22mm pipe out of the tank) narrow to 15mm before they go around the house. So we are effectively using a 15mm as opposed to 22mm plumbing system.

The plumber reckons this is the cause and to rectify will involve setting up a parallel 22mm line up to the top floor, capping off the 15mm pipes and feeding the local 15mm pipes from the 22mm, and perhaps backfeeding the system so that we get max pressure at the top.

It sounds reasonable to me, but as it is a fairly big job, my plumber recommended I get a second opinion...so the question is...is this a likely cause of the problem and will the recommended fix make a reasonable improvement? Anything else to consider?

My first posting, thanks for your time

J

 

[Bernie2]

Hi! J,

I would do the obvious thing first and go to the first entrance point of the mains water into the house and do a flow and pressure test there.

Then work it out for the three properties.

1 bar should shove a column of water up in the air 10 meters or so. But then you have to take off the pipework resistance factors.

It can take a bit of time to do, but compared to the cost of spending out for work that may or may not work, it would seem a sensible thing to do anyway.

Bernie

 

[Draez]

Thanks for the response Bernie2,

It's just the one house that has the problem, and the flow was measured from the kitchen tap which is right next to where the mains supply is. It was v good, at least 1 bar though I forget the actual figure.

I'm guessing that if the pipe is too narrow, the flow will have a job getting to the top of the house...

 

[justlead1]

Hi. Calculation can be done as Bernie says. But pipe size and corrosion of pipes and fitting all play there part in poor performance. If is a three story house with 3m story hights with only 1 bar at ground floor you will loose 0.6 bar before you look for head loss via frictional resistance. Connecting a length of say 25 or 20 mm MDPE to the tap at ground level and running up the stairs to a third floor delivery point and turning on tap, will give you some idea of the benefits of installing larger pipe work permanently. With out the expense of a failure. Good Luck

 

[Bernie2]

Yes! Justlead has given a simple straight forward way of testing things.

I assume of course you have checked outside to make sure the external stop tap is fully open?

Just off the cuff, whilst you may have 1 bar, its not much really for what you want to do, but 1 bar 9 litres flow is all you can really expect in some areas.

The thing is, even if you use a bigger pipe size you will not increase the pressure, only the flow rate and then it may have problems if the house communication pipe is only 15mm.

Have you asked your water supplier, can they do anything to improve matters?

 

[Draez]

Cheers guys

I've emailed the plumber with the ideas. The pressure downstairs is good though so things do point to a pipe problem.

Best wishes Jon