Hot water piping

[zeegoman]

I am having to upgrade the plumbing to the current bathroom. I also have to take off for a new ensuite which will have hot water to basin only. Is it worthwhile reducing the hot water pipe from 15mm to 10mm?

What are the effects likely to be, i.e. will I be able to fill a bath in a reasonable time?

I have a combi boiler.

 

[chrishutt]

The advantage of 10mm over 15mm is that there is less standing cold water to draw off before the hot comes through, plus it is easier to install, being more flexible.

The disadvantage is that it will tend to restrict the hot water flow, but this might not be disadvantageous with a combi boiler. It's possible to calculate the result based on combi output, hot water flow rate and length of 10mm run.

However it might be simpler to connect a similar length of 10mm tube up and just test it empirically. Bear in mind that hot water temperature from combi will vary with cold mains temperature so at the moment it will be lower. You could certainly use 10mm for basin supplies.