New water supply pipe what size feed into boiler?

[Jamesc1234]

Hi guys,

Need a little help here and very new to all of this.

We have a Victorian house and are struggling with low water flow, although pressure is ok. We want to have a decent thermostatic shower. Currently it is on a common supply pipe and we are house number 5 and it has a combi boiler. The (hopeful) solution we settled on was a new water supply pipe.

A new 25mm MDPE pipe has been put in and is going to be connected to the water main. We thought it would be best to feed the new water supply into the boiler to deliver it the greatest flow rate.

The plumber came this morning to fit the internal stop tap and make the connection into the house system.

He has connected the 25mm supply pipe onto a 15mm copper pipe, which then runs to a T junction and splits into 2 x 15mm pipes, one which supplies the boiler and the other which supplies the rest of the house cold.

Given that we want maximum water flow to the boiler and also to stop the problem with flushing toilets/taps/washing machine at the same time, should he have run 22mm pipe up to the T junction?

Have attached a photo. Any advice greatly appreciated.

 

[ShaunCorbs]

Me personally I would, did you tell the plumber you wanted it in 22mm ?

 

[Last Plumber]

I would have at least run it to a 15 x 15 x 22 tee, yes.

It is however only very short and it may not make a massive amount of difference in all fairness.

What's your pressure and flow rate at the nearest draw off point to the stop tap?

 

[Scott_D]

What size combi is it?

 

[Chalked]

Would have been better. But that 15mm main will have more capacity than your combi can use.

 

[Jamesc1234]

Worcester Greenstar 29CDi Classic 30Kw.

Should I ask the plumber to change it to a 22mm pipe? I'm concerned that as it is not supply the maximum flow at the T junction that when we turn on a tap etc, flow to the boiler will drop.

 

[ShaunCorbs]

Cold tap and a hot tap

Or two hot taps open ?

 

[Jamesc1234]

Just if the shower was on and then someone turned a hot and cold tap on at another basin, for example

 

[ShaunCorbs]

Do you know your new pressure and flow rate

Also that's standard for a combi will always do that

 

[Jamesc1234]

no, we're not connected to the mains yet. tomorrow. potentially could check pressure/flow then. Just really if it needs changing I want to do it before the plumbers leave.

 

[Vee]

It will help if you make sure your shower head is a water saving one.
Data from Worcester for Greenstar 29CDi Classic
Hot water flow rate 35°c ∆T (litres per minute) 12.3l/min
Hot water flow rate 40°c ∆T (litres per minute) 11l/min

 

[Last Plumber]

I would see how it performs. Like I said earlier, I can't see it making a massive difference over such a short length but it depends on the pressure and flow you have.

 

[Jamesc1234]

Was this the best way to connect the new water supply into my system? Could it be improved?

 

[ShaunCorbs]

Since the rest of the run is in 15mm no but wouldn't harm / would benefit if you could put the boiler feed in 22mm as far as you can

 

[Jamesc1234]

So I should ask him to change it to 22mm pipe from the 25, which splits into 2 x 18mm pipes at the T junction?

 

[Jamesc1234]

I have connected the new pipe and opened it up.

New flow rate at the kitchen tap (i think it's the 1st tap) is 15l/min cold and 10l/min for hot.

Definitely an improvement, but wasn't as fast or powerful as I was expected. The hot rate I understand is limited by the boiler, but the cold?

Any thoughts? Decent enough to run a thermostatic shower?

 

[ShaunCorbs]

Yes should be fine aslong as no other outlets are open

 

[Jamesc1234]

Thanks for your advice.

Any thoughts on why the cold flow rate isnt that high? It's a Victorian house so I was wondering if its all the old pipework, bends etc.

 

[ShaunCorbs]

Thanks for your advice.

Any thoughts on why the cold flow rate isnt that high? It's a Victorian house so I was wondering if its all the old pipework, bends etc.

Could be but depends what your getting from the water board if you phone them up they should be able to tell you

 

[Scott_D]

Does the kitchen tap have narrow flexis?
Try an outside tap