Pipe size dilema - 22mm or 15mm?

[ReadySalted69]

I'm fitting 22mm flow and return pipes between ceiling joists that will drop down to radiators below (forming inverted loops).

The drop from the ceiling to the floor is 2.7m and a further 1 to 2 to meters to reach each radiator. I have the space to use 22mm drops all the way right down to the floor in most rooms and then reduce down to 15mm tails for the last meter or 2.

Is it advantageuos to run 22mm pipes all the way in this manner or should I just use 15mm drops from the ceiling and not worry about it. This would mean runs of about 5m in 15mm pipe to reach each rad in some cases?

Why is it better to drop down from 22mm to 15mmm below the ceiling level if aesthetics are not a concern?

 

[45yearsagasman]

Very rarely on a small to medium sized system would you need to drop in 22mm.
If you are only piping one rad per drop then 15mm should suffice.
You don't say what other rads are connected to your system.
Looks aside, the cost of 22mm and over engineering should be a consideration. A normally piped system using 22mm main circuit and 15mm drops will work perfectly after balancing has been done.