On Wed, 17 Jun 2020 13:10:21 +0100, John Rumm wrote:

All hot water radiators output their power almost entirely by convection.

Its typically about 80%/20% at a 70 degree flow rate.

Also worth considering is the effects of the adjacent wall. A radiator
will heat that by radiation, and you will get a boost to the rate of
convection from the "hot" wall.

(also counter intuitively, its common to place reflectors on outside
walls to reduce transmission through the wall - however in doing so, you
lose the convection boost you get from local heating of the wall
surface. It might save energy, but make the room actually feel less warm).

I'd prefer to save the energy. There is CWI but the heat gets through to the
cavity eventually and there'll be a bit of convection through the rock wool.
The reflector will reduce the rate of radiation from the rad as it's sending
some heat back into the rad - nett IR. There could be, I suppose, some
increase in convection due to the rad /not/ being cooled quite so much.

My new rad calls for at least 15 cm clearance from the floor so that
convection isn't impeded; I wonder how convection is affected by gap from
wall to rad.
--
Peter.
The gods will stay away
whilst religions hold sway