Calvin wrote:
I don't think that's right. The fin design on all radiators I've seen
is pretty basic - no more than a thin sheet of steel made into a wavy
shape and spot welded to the panel.

There is one corrugated fin, spot welded on at about 15mm intervals.
Let us say there's two fins per inch.

On proper heater batteries, the copper pipes are passed through ali or
copper sheet fins which have holes punched in them. 12 or 18 fins per
inch is not unusual. The pipes are hydraulically expanded to ensure a
wide contact area between the pipe and the fin metal.

Now, why do you think they'd do all that? Do you think it might be
possible that the amount of heat transferred is somehow related to the
surface area of the heated metal?

Next time your heating is on try
feeling the temperature on the panel, on the fins near the panel and on
the end of the fins furthest from the panel.

Granny. Eggs. Suck