In an earlier contribution to this discussion,
John Stumbles wrote:

[I'm posting this to the group as it was emailed to me from someone
who presumably found my article on rad outputs on the wiki.]

I have been searching for these specs since I had my old ones
replaced by modern convectors in Feb this year with DISASTEROUS
RESULTS.

Those old steel panel rads with no fins had amazing radiaant heat
transfer properties, and I did not know that they just needed
FLUSHING THROUGH, or what benefits they had over the modern
convectors, until I changed them, to my great regret, too late.

I did find a website which gave the heat output for the old obsolete
rads, and found that my 58cm high and about 47inch something wide old
ones had a wattage of about 1000.

Similar modern ones today, are 752W with no fins. Researched that" the
powers that be "have thinned the steel down over the years and my new
ones are the now new regs of 1.20mm of cold rolled steel plate, which
do get hot but do not radiate or give off the intense heat that my
old ones did.

Also the INERTIA has been reduced to make the rads lose their heat
quicker, and so do I!

My old ones kept hot for a very long time and reduced their heat very
slowly, enabling me to turn off boiler at a low air temp. of 20.5,
and I remained warm for 90 minutes, 20 mins after the rads were cold.
Very energy saving.

With my new convectors, I and all my FEMALE friends and relatives, do
not feel even warm enough at 24 degrees, and as rads lose their heat
quicker, I keep shivering, which I never did at a much lower air
temp, with my old little miracles I lost. And the new energy saving
boiler had to be on constantly, drying out the air, but still not
getting me warm at even 26 degree AIR TEMP Humidity in room went
down to 29% and I had a dry mouth breathing in the uncomfortable too
dry air.

My old ones gave me a healthy humidity of 48% at 21 degrees, and cosy
warmth.

You are a man, and do not feel the cold as much as we females, or
react to sudden loss of heat as we do - the men I know say they
always hot.

Also, I was surprised that, with my old ones, the night min. temp in
my front room, which is all glass and open plan to a glass front door
and 9 squ m unheated kitchen, with just 1" of glass wool in the
ceiling of my bungalow, lost only 2 degrees ( from 20.5 - 18.6),
during -4 degrees of frost in the night, with no heating on.

But my convectors cannot do this, and with +6 min in the night, my
front room min temp went down by 10 degrees!!!!!!

My rearch on the web, explained to me that the old rads gave off a
powerful direct to the body heat, which also warmed the walls and
solid objects, which convectors are not good at doing, and the walls
gave back their heat in the night when the ambient air temp reduced.

My scientific brother, who worked on aero combustion, said radiators
all work by convection, NEVER by radiation, as that is only possible
with electric, open fire flame or sources from the sun!!!!!!!!!!!!
And is insisting that the old rads could not be any different from
the new ones.

I know they have made the steel thinner and indeed they sound more
like TIN when tapped. The old ones CLONKED. so I have been trying to
find the specs on the old ones to prove to my brother than I am not
insane!!! And the water content has been lowered, so heat output is
lowered.

I found a website, which explained everything that happened when I
changed my old non-finned rads for convectors, and that is Energy
Saving Now, with particular reference to " The mess with radiators"

Also the shivering was explained in one of the other sections, about
heat from the fins of convectors losing heat quicker than the
waterfilled panals, and the body reacting by "feeling a sudden
freezing" and reaching for room thermostat to bring on the heating
again so soon. using more gas than is necessary with the non-finned
rads. Which is exactly what I did.

He especially refers to the benefits of the old obsolete rads for
older not so well insulated houses, and the inappropriateness of
convectors in such houses.

He went as far to say that "science had got it wrong to make them
obsolete, by deeming them inefficient".

I have learned this all too late. After the flushing through of the
old ones, they gave out such a powerful direct to body heat that even
the plumber thought the rooms were 10 degrees higher than my
thermometers said, and in his ignorance, he claimed my thermometers
were all wrong, which they were not.

So, my message for you is that the old obsolete rads are BETTER than
the new convectors whether for old or new houses. And to keep them
as long as they last.

In fact, I have been searching to find these old rads to swop with my
new ones, but in vain

I would be very interested in any pecs you have of the 60s and 70s
rads, to prove to my brother how they HAVE changed.

He has 1984 rads, most without fins, including a double with no fins,
but has no way of knowing their technical heat outputs, but assumed
what they were, from comparing them with today's - grave error, as
the sizes have reduced their output.

I read on one website that in 1997, new regs forced rads to reduce
their output by 11% and asked WHY? But there was no answer.

Do not know if you will receive this e-mail as I wanted to reply on
the website, but too complicated for me to LOG IN, I,m afraid.


[Reminder: the above is what was emailed to me, not my own words]


Is it worth answering, I ask myself. Probably not, but I'm going to anyway!

I'm afraid that the above outpouring demonstrates a complete lack of
understanding of the laws of physics.

The heat given out by a radiator depends almost entirely on its surface area
and on its mean temperature relative to room temperature (delta-T). The
thickness of the steel from which it is constructed matters not one iota.
Size for size, a radiator with fins will give out more heat by convection
than one without because of the increased surface area over which the
convected air passes. The heat radiated (which is relatively small compared
with convected heat) will be much the same between finned and unfinned
radiators.

It is true that radiator manufacturers are now quoting lower output figures
for a given size and construction of radiator than they used to. This is
*purely* because they are quoting the output at a lower delta-T value to
relect the fact that modern condensing boilers run at a lower water
temperature than 'conventional' boilers. Hence, if you replace a
conventional boiler with a condensing model - and run that at its most
efficient condition - radiators which were previously adequate may no longer
be so, and may need to be replaced by larger ones - or by rads of the same
size but with fins.

The OP's problem is almost certainly down to incorrectly spec'd finned
radiators for use with the new boiler rather than to there being anything
inherently wrong with finned radiators.
--
Cheers,
Roger
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