On Thu, 6 Aug 2009 10:19:40 +0100, "Roger Mills"
wrote:

It depends on what percentage change this represents! You'd be more likely
to notice the difference between 300 and 600 than between 2300 and 2600.

Very true! I shall have to calculate the percentage difference.

To at least a first order of approximation, all radiators of a given size
and construction should give the same output under the same (Delta-T)

The output depends on:
* surface area of the panels and fins
* emmissivity of the surface finish
* mean surface temperature

None of those things are going vary all that much from make to make.

That's what I thought, which is why I was surprised that the outputs
differed. Perhaps some marketing departments "tweak" their figures
more than others?

I am currently looking at a Quinn Barlo 500x1400 double (2.3kW, 7900
BTU IIRC). Is Quinn barlo a good make? I think it's the least I can
do, since Barlo were kind enough to provide the calculator

I have looked at other makes 500mm high and double width to produce
the same output; one required 500x1600 but another managed with just
500x1300. I am surprised that 160mm in one outputs as much as 1300mm
in another; I would have thought a foot difference in length would
have made a big difference to output.

Are you sure that all the examples which you cite are specified at the same
dT?

Yes, after all your previous help with factors, I checked, double
checked and checked again! Only Toolstation and 4bathrooms quote
dT=60, everyone else is using dT=50

Thanks again.
Stephen.