Pipe sizing from and to combination boilers

gary50 · Mar 17, 2017

Hi Guys,

Ive been in the game for 15 years now and would like to know others opinions on a matter:

Basically is there any benefit from running 22mm main into combi and 22mm pipe out to all outlets.

The way i see it is even if you have 30lpm on incoming main then combi will reduce down to its given flow rate (lets say 15lpm) so pointless doing it.

The builder i work for has said he wants everything in 22mm then reducing down at last points as you would with unvented.

Im hoping someone can tell me I'm right and give me some reasons why not to run in 22mm to shove back at him!

I personally think having all pipe work in 15mm is acceptable.

With the above scenario even with two bathrooms would increasing pipe sizes help with volume of water in any way?

Thanks!

newcastle phill · Mar 17, 2017

I cant see the point..if anything its wasteful.
All that extra volume of 22mm stone cold water needs displacing with hot.

Obviously exceeding certain flow speeds increases noise - but never had an issue with a combi - Even bigguns..in domestic properties

Last Plumber · Mar 17, 2017

No point
phil is right

Last Plumber · Mar 17, 2017

No point
phil is right

SimonG · Mar 17, 2017

Its only a 15 out. Why waste money. Builder wants a slap and stick to bricks and mortar.

Best · Mar 17, 2017

Even on an unvented hot water system to use 22mm on entire run of hot pipe can be wrong. When you open a hot tap you could wait an entire minute before the hot water fills the pipe and comes out of tap. Very frustrating and waste of hot water. Tell the builder that!
Although I hate the stuff, - 10mm pipe on branches to taps on unvented or combi systems gives a speedy and less wasteful hot flow.
To be fair to the builder, he is thinking about it being done with good flow, but he isn't the plumber.