On Thu, 06 May 2021 14:44:43 +0100, charles
wrote:

snip

'vertical radiators are less *effective* at heating a room than
horizontal ones'

So, you choose a slightly larger one

But that's not a solution to comparing the effectiveness of vertically
or horizontally orientated radiators of the same volumetric flow etc.
;-)

The thing that doesn't change in the comparison is how a 'third party'
acts to / with both orientations, namely the air.

Because 'heat rises', the more radiator you can expose to more virgin
air the more likely you will transfer more heat between the water
rad air.

Cheers, T i m