Set Square wrote:
In an earlier contribution to this discussion,
Calvin wrote:


IR thermometers are the work of the devil. They are *very* difficult
to use and even in the hands of an expert can often give misleading
results.

That is cobblers! They give very quick - and reasonably accurate - readings,
which is what you need when you are checking a *lot* of radiators in quick
succession. If you stick a little square of black tape on each bottom corner
of each radiator - right next to the input/output connections - you can get
very consistent results. The readings don't need to be accurate to a
fraction of a degree because you are measuring the *relative* temperature
drop across a number of radiators. This is by far the quickest way to do it.
--
Cheers,
Set Square
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Sorry, I'm in a bit of a bad mood today and my previous post was a
little simplistic. Allow me to explain...

IR thermometers measure IR radiation and from that infer the
temperature of the object. Which is great if other significant
variables are controlled but all too often they are not and as it's
(non-visible) IR we're talking about generally the user isn't even
aware the variables exist.

In the case of a home user measuring radiators in a number of rooms the
result is going to altered by the surface finish of the radiator: one
that is matt black (or with your black sticky tape on it) will tend to
give a more sensible reading than one which is highly reflective to IR.
Indeed, depending on the size of the measuring spot on the meter, one
which is highly reflective to IR might even give a very different
reading as the meter is moved so that it points to a different part of
the "fold" of the surface.

The ambient IR will probably also be different from room to room and
will change the results although for the task of radiator balancing it
shouldn't change the differential.

My job sporadically involves worrying about how hot various bits of
electronics get during operation. Usually when things have already
gone wrong and we're looking for a cause. An IR profile of a PCB can
help but it can also mislead you if you don't understand what can
effect the readings. (IR measured temperature of the case of that
polished-top IC - that'll be the temperature of the ceiling then sir).

As for the OPs situation I wonder if he's using the sort of meter which
re-calibrates each time you press the ON button and then shows a live
reading as you move it around. If it is one of those then he's
probably just listed the temperature delta between some random
floor/wall/whereever-he-was-pointing-it-at when he pressed the button
and the radiator itself. The common sense rule still applies: if it
feels hot it certainly isn't 20-something C.