HELP-which plumber is right?

[matt1098]

Apologies in advance for seeming rather vague but I hope those with more knowledge than me will be able to fill in the blanks and will be able to give a view as to who is right in this scenario:

Im currently getting quotes to replace my boiler with a combi. The existing system I have is old and is located downstairs in a 3 bed semi. I would like to move the new boiler into another room at the same time as changing it to a combi. Anway my question relates to the width of the hot and cold water pipework which is currently 22mm. As I undersatnd it the same pipework that will feed from a combi will be 15mm. One plumber is saying that to do the job properly he would quote for replacing all the 22mm with 15mm for the whole of upstairs (single bathroom- bath and sink ) as to leave the 22mm would give a disapointing result (presumably flow). He thinks the downstairs is already 15mm.

I should add that the proposed combi will be a good one- Worcester Bosch or Valliant with a flow rate of about 15 litres per min and also that I have very very good mains pressure.

I never was very good at physics but I struggle to see how the amount of water that will come out of an upstairs tap will be effected by whether its coming out of a 15mm or a 22mm pipe. Sure on the 15mm it will come out under a higher pressure maybe, but there wont be anymore water. That maybe wrong, Im not sure. If there will be a difference can someone explain what it will and what effect it will have? I should also add that I plan to fit a thermostatic shower upstairs in the near future so not sure if that changes things

Are there any plumbers hovering that could give us a view or people who have had the same question?

Thanks in advance for any help

 

[simond]

The larger bore pipework will make no difference to the flow rate achievable at the tap, other than marginally improving it due to lower pipework resistance.

What your plumber may be alluding to is the latency of hot water supply. If you have a 22mm + xmetres pipe of cold water to empty before the hot comes through, it will take a little more time, and consequently waste some water.

If he used the 'lower flow rate argument' as you suggest, he is a numpty.

 

[holty]

you've gotta think logically if you buy a new mono block tap with 10mm tap tails. doesnt matter if you had 28mm going to them.only the volume of what the 10mm can take, can pass through it.like simond has said it will just take longer to reach the taps.but shouldnt hinder performance.

 

[matt1098]

The larger bore pipework will make no difference to the flow rate achievable at the tap, other than marginally improving it due to lower pipework resistance.

What your plumber may be alluding to is the latency of hot water supply. If you have a 22mm + xmetres pipe of cold water to empty before the hot comes through, it will take a little more time, and consequently waste some water.

If he used the 'lower flow rate argument' as you suggest, he is a numpty.

Thanks very much Simond. He didn't really explain why he would do it that way and the raeson we ended up discussing flow rates was because that was what I assumed he must be getting at. I suspect he doesn't really know why he would re-fit 15mm, just that he has been told somewhere along the way that this is the best method (Im not sure).

Anyway-Im not worried by a bit of wasted water. What would you do if quoting?

Thanks again

 

[simond]

I would inspect what you have already.

What I have learnt from years of 'quoting' is that a prognosis without the benefit of being onsite is both misleading and worthless.

 

[holty]

you'd be surprised at how many customers moan of wasting cold water to achieve getting hot water.just ask for a quote without the extra work.

 

[matt1098]

I understand Simond. I guess Im just trying to understand what is the common or accepted practice in this scenario and if there is a right or wrong answer.

Ive dones as suggested Holty. Thanks for your input, v helpful

 

[gas4you]

In a perfect world where money was no object, then changing all the hot pipe work to 15mm would be slightly advantageous.

In the real world this does not happen, so stick with whatever you have got and save some money.

 

[holty]

In a perfect world where money was no object

if only

 

[bengasman]

Assumption is the mother of all..........
The installer was right in saying that 22 mm on a combi is not ideal. Whether it is worth replacing if in good nick, questionable. If there is a long run from the boiler to the taps, it could take a while before the water gets fully hot.

 

[Biggles..]

Never assume,always check cos it'll make an A S S out of U and ME

 

[Agile]

Thanks very much Simond. He didn't really explain why he would do it that way and the raeson we ended up discussing flow rates was because that was what I assumed he must be getting at. I suspect he doesn't really know why he would re-fit 15mm, just that he has been told somewhere along the way that this is the best method (Im not sure).

Anyway-Im not worried by a bit of wasted water. What would you do if quoting?

Thanks again

Its an unfortunate fact of life that many plumbers are not very eloquent and consequently have difficult explaining themselves.

However, regardless of the reason he knows that 15 mm is better!

There are two aspects and neither properly addressed in most cases!

Hot supply pipes should be insulated. To insulate the 22 mm will lessen the impact of not changing it to 15 mm.

I would explain the disadvantages and quote for the extra to-

a. Insulate the 22 mm existing if thats feesable.

b. Replace with insulated 15 mm.

But then I am well able to explain myself in words and script.

Tony Glazier

 

[dextrous]

But then I am well able to explain myself in words and script.

Tony Glazier

I think we'll be the judge of that Tony