I have a tall 'designer' style radiator in my bathroom which has never
worked satisfactorily. In investigating this I have found that the
design which is a hollow tube at the top and bottom which are connected
by 8 fins can never have worked as the tubes at top and bottom are
straight thru' ie with the valves removed I can see straight through.
Therefore the water passes through the bottom tube without circulating
through the fins, hence the rad just gets a bit warm through
conduction. Both top and bottom tubes are straight thru.

It would seem to me the bottom tube (this has the valves) should be
blocked half way along so the water is forced up the left 4 fins and
down the right 4 fins.

The supplier (a bathroom showroom) have said they'll need to talk to
their tech guys but my question is : would a radiator normally have to
have some sort of baffle or shield to force the flow of water around
the rad ? It strikes me the rad is perfect for horizontal orientation
but would cannot possibly work vertically.

Has anyone else heard of this ? I'm hopeful the supplier will come good
but wanted to be a bit better informed in case of any 'discussions'
with the supplier !

thanks

wrote:
I have a tall 'designer' style radiator in my bathroom which has never
worked satisfactorily. In investigating this I have found that the
design which is a hollow tube at the top and bottom which are connected
by 8 fins can never have worked as the tubes at top and bottom are
straight thru' ie with the valves removed I can see straight through.
Therefore the water passes through the bottom tube without circulating
through the fins, hence the rad just gets a bit warm through
conduction. Both top and bottom tubes are straight thru.


It's called convection. The hot water rises to the top through the fins
and the whole radiator gives off heat.

Have you tried bleeding it?

Have you tried balancing it?

Have you read the central heating FAQ at
http://www.diyfaq.org.uk/contents.html?

MBQ

Therefore the water passes through the bottom tube without circulating
through the fins, hence the rad just gets a bit warm through
conduction. Both top and bottom tubes are straight thru.

Convection within the radiator should enable the heat to reach the top,
unless I have misunderstood your description of the radiator.

Perhaps the rad is not full of water? Is it so tall that it is taller than
your header tank? Has it been properly bled until water comes out the top?

Also, many "designer" radiators have pitiful heat outputs, being designed
for looks rather than performance. Are you sure you aren't getting the full
output?

Christian.

How can convection occur if the water is flowing into the radiator and
straight out the other end of the tube (300mm) - the water has nothing
to make it flow the 1800mm up to the top and down again.

It has been bled, balanced, you name it !

The stated output is around 1kW so would expect it to get pretty hot -
it has never got more than lukewarm I believe due to conduction from
hot water passing through bottom tube.

How can convection occur if the water is flowing into the radiator and
straight out the other end of the tube (300mm) - the water has nothing
to make it flow the 1800mm up to the top and down again.

It has convection. It works there is hot water at the bottom and cold water
at the top. This situation is not sustainable and the hot water will rise
and the cold water will sink. Almost all radiators work on this principle
and a standard horizontal radiator has nothing to deflect water upwards.

The stated output is around 1kW so would expect it to get pretty hot -
it has never got more than lukewarm I believe due to conduction from
hot water passing through bottom tube.

Is the very bottom of the radiator very hot?

Christian.

The bottom gets very hot - as the bottom tube is very short 300mm and
the height is 1800mm that is why I think deflectors or some device to
direct the water will be required

wrote:
The bottom gets very hot - as the bottom tube is very short 300mm and
the height is 1800mm that is why I think deflectors or some device to
direct the water will be required

Does the pump speed make a difference?

MBQ

The pump is already on high setting. The system is fairly large, 13
rads I think. The bottom gets extremely hot so cant see its a problem
with enough water getting to rad

The pump is already on high setting. The system is fairly large, 13
rads I think. The bottom gets extremely hot so cant see its a problem
with enough water getting to rad

Perhaps it is too fast and interferes with the convection. Try balancing the
radiator right down.

Christian.

wrote:
The pump is already on high setting.

That may be a contributory factor.

MBQ

On 17 Jan 2006 07:48:38 -0800, wrote:

|The bottom gets very hot - as the bottom tube is very short 300mm and
|the height is 1800mm that is why I think deflectors or some device to
|direct the water will be required

Then convection should get the rest hot. Have you taken it off the wall
and filled it with water, to see if the fins are filled with crud?
--
Dave Fawthrop dave hyphenologist co uk
17,000 free e-books at Project Gutenberg! http://www.gutenberg.net
For Yorkshire Dialect go to www.hyphenologist.co.uk/songs/

The water in it is completely clear so dont think is blocked at all.
The radiator is new as is most of the CH system

The message . com
from contains these words:

How can convection occur if the water is flowing into the radiator and
straight out the other end of the tube (300mm) - the water has nothing
to make it flow the 1800mm up to the top and down again.

It has been bled, balanced, you name it !

The stated output is around 1kW so would expect it to get pretty hot -
it has never got more than lukewarm I believe due to conduction from
hot water passing through bottom tube.

If you had managed to balance the radiator the output temperature would
be 11 degrees C below the input temperature. If the hot water flows
straight through with no reduction in temperature then it has not been
balanced.

ISTM that if there is no reduction of temperature across the the
radiator then you effectively have a temperature inversion within the
radiator which would prevent normal convection. The solution (assuming
the radiator problem is capable of resolution) is, as others have
already said, throttle down the flow through the radiator until
convection circulation does start. 300 mm seems very short to me but
would a manufacturer actually make and sell a radiator that wouldn't
work properly under any circumstances?

--
Roger Chapman