On Sat, 2 Dec 2017 08:52:55 +0000, Vortex12
wrote:

In New Year will be replacing an ancient heating system in a flat. Total
8 radiators with all the piping logically coming back to a single
central point.

I am thinking an 8 way UFH manifold (John Guest) would make a very
elegant solution at this location.

Of course flow temperatures may be 60+ degrees, whilst normal UFH
temperatures are much lower.

Can anyone reason not to use this approach?

I did this in a house 40 years ago using a copper manifold and
conventional radiators and it is still working. The manifold approach
and 8mm microbore was used because a large underfloor void made it
very easy to pipe to all the radiators in 8mm and speedfit hadn't been
invented or wasn't common. Upstairs was done similarly using the
airing cupboard for the manifold location. I think I oversized the
radiators a bit but I've long lost the calculations I did.