hot water pipes 15 or 22mm

Simple question is should long runs of hot water pipes be done in 15 or 22mm.

My hot water tank to my kitchen sink is approx 16m. If i run 15mm i guess it will cool quite alot before reaching it. If i use 22mm i guess you will have to run the tap for a while before the hot comes through. What is best.

Also, i intend using mainly plastic pipe now since the increase in copper prices seems to make this more reasonable now and it is certainly quicker. Especially when i have most of a house to build. Is this better at heat loss? I assume copper conducts more so radiated more heat along the pipe.

Normally 15mm should be adequate

What isn't 'normally'?

A 16m run with only 1m head of water.

22mm has at least twice as much water in it so that means you have to pay extra to heat that water up

Insulate the pipe if you are concerned about heat loss.

I would use plastic unless the pipe was going to be left visible. Watch the forum ... theres a big topic on about plastic vs copper at the moment

Its a 16m run but not all horizontal. It comes from the hot water tank that will be on the first floor downs and along the kitchen wall, across the back of the kitchen and along the opposite kitchen wall to the sink. THis is abou 12m horizontal and 4m vertcally.

All the pipe work will be outo of sight so i will do it in one roll of plastic. Much, cheaper and easier and safer as there will be no joins anywhere.

Not particularly worried about heat loss, just didnt know whether this was an abnormally long run.

15mm will do

'Safer' if you havent got vermin that is