Roger Mills wrote:
In an earlier contribution to this discussion,
Stephen wrote:

Hello,

I see Screwfix list radiators with outputs calculated at dT=50C,
whereas Toolstation list their rads with outputs calculated at dT=60C;
this makes comparing them difficult. Am I right to think that for
condensing boilers you want to aim for a dT=50C?

Yes, or even less. Very few systems with conventional boilers run at a dT of
60 - 55 is more usual.

To convert the toolstation outputs to dT=50, do I just divide by 60
and multiply by 50?

Not exactly - it's not quite linear. The factor given by Stelrad is 0.798 -
whereas 50/60 gives 0.833

strictly you should take your target room temp - say 20C - subtract it
from both rad temps, and then use that..so 60-20=40, and 50-20=30, so
output will be 35/40 or .75..

one guesses that stelrad are rating for an output room temp somewhat
lower - say 17C or so.