Domestic Hot Water Pipe Size

[David Jobes]

Hello there. I am planning on turning a spare bedroom in my house into a bathroom. I have the required permission from the local authorities and have had a couple of local plumbers out to have a look and give estimates. To be honest the pipe work is something I would like to do myself as I have done this work in the past prior to getting someone out to give it the once over so to speak.
I have a Ferroli 24b condenser fitted. I have a problem in my existing bathroom where when I run the hot tap on the bath all hot water flowing from the basin stops. In the same manner when I run the basin hot water all hot water from the kitchen sink is stopped. The kitchen sink is closest to the boiler, then the basin and last of all the bath. Both plumbers told me that the bath was "stealing water from the other end users" but both gave me different ways this could be stopped.
One of the lads advised that all the pipe work should be 22mm reduced down to 15mm when it reaches the end user so as to give greater pressure. The other said the boiler was not big enough and all hot water pipe work should be 15mm. The pipe work at the moment is 15mm!! The boiler is only max 4 metres from the furthest end user and I find it strange that this is happening. Can someone advise on the correct manner for plumbing in the hot water as I intend to run a new hot water supply from the existing boiler position to the new bathroom which will be approx 7 - 8 metres to the final end user. I am 90% certain I should use 22mm reduced to 15mm but I just need some advice.

Hope someone can help

Best Rgds

DJ

 

[doitall]

Most Combi's will only supply 1 outlet at a time, changing to 15mm will not alter that, True it will give give the impression of a higher pressure, but the ltr/min will be exactly the same from the boiler.

Your best bet would be to find space for an un-vented cylinder, and connect both bathrooms to it, leaving the combi to supply the kitchen/utility.

 

[David Jobes]

Ok thanks for that info.

Once I have created the new bathroom I will be getting rid of the old one as this area will become part of the kitchen. Is it normal practice to use 22mm down to 15 then with hot water or is this not really required ??

 

[doitall]

Very normal, with a pressure system (combi)

 

[chrishutt]

If you're sticking with a combi system for the foreseeable future then there is no point in having pipework above 15mm size. In fact having any 22mm will increase the amount of cold water that has to be drawn off before the hot comes through and will leave more hot water in the pipes afterwards so wasting energy. Do not use the plumber who suggested using 22mm.

 

[David Jobes]

"If you're sticking with a combi system for the foreseeable future"

Is it worth me changing the boiler for something else. Someone mentioned to me that the regulations these days stipulate a condenser type boiler. I dont know a great deal about them to be honest. Can anyone recommend a decent boiler that satisfies the regs and will give a decent hot water flow??

 

[bengasman]

Chis is right, unless you are looking at a combi of more than 40 kw output, you don't need 15mm
stating the obvious, the flow will be limited to the smallest pipe downstream.
whoever advised you 22 mm has no clue