In an earlier contribution to this discussion,
Jim wrote:

With regard to the second possibility:
Is the radiator getting as hot as those in the other rooms? How long
can you hold your hand on it?
Is it getting hot as *fast* as the others?
Is the heating being turned off by a room stat elsewhere before the
lounge gets up to temperature?

Rad heats are fast as others in the house, and gets very hot (touch
for about 1 second). At the moment I am running the lounge rad
without the TRV set to max, and the house room stat in the lounge to
make sure that it is not the room stat.

Not sure I understand the TRV comment. Are you saying that the TRV *is*
throttling the flow? If so, set it to max, or remove the head completely.

I have tried the heatloss program, but I am not sure what to enter
for the Gas Warm allowance, or the Airchange rate. I have selected
Gas Warm allowance as YES and a air change rate of 1.5? This returns
a value of 1866 watts. Assuming the gaswarm allowance and air rate
changes are correct this appears to show that the current rad is
underated by around 25%
By using the same size rad, in a double panel 2 fin conventor should
acheive about 2150 watts, which give around an extra 650watts and
should be overated by about 15%.

Do these conclusion sound reasonable, before I buy a new rad!

Looking at my radiator catalogue, I guess that 2150 watts for a
double-finned 1100 x 700 is based on a delta-T of 50, whereas you may be
able to achieve 55 and wring a bit more out of it.

Is your 1866 watts heatloss the steady-state value - or does it have any
bunce in it (typically 10 - 20%) to provide a fast warmup? Provided there
*is* some bunce, and provided the boiler and pipework can deliver the extra
heat fast enough, this rad may well be ok.

It's worth trying a few different values for some of the parameters in the
heatloss program to see what difference it makes. For example, what is the
effect of saying NO to Gas Warm allowance, or going for 2 air changes per
hour? [1.5 is probably ok unless you've got a lot of draughts - but it's
always useful to know how much you've got in reserve in case any of your
assumptions are wrong!]
--
Cheers,
Roger
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