what colour on rads will radiate most heat?

pensioner_margaret

A plea to experts on elementary physics.-
I vaguely remember my O level physics lessons of 50 years ago. I seem to recall that matt black surfaces radiate more heat than pale shiny surfaces. Is my memory correct?, and if so should I paint my wall mounted Winterwarm electric heating panels matt black.- will it really make enough difference to compensate for them looking obtrusive?

Mr_Grumpy_7

I too seem to remember that a black surface will radiate heat best, and will also absorb heat best. That being said, I would not have thought the difference would be enough for it to be worth putting up with having black radiators.

joshm_2

I think the idea of a black radiator being more efficient might stem from the idea of the theoretical "black body" from our old physics lessons. I don't think this necessarily applies to radiators!

Hopefully some science buff will correct any errors or bad assumptions, but:

Heat from radiators comes in two forms, convection and radiation. I don't know the ratio that applies to typical radiator regarding convection output & radiation output, but it's worth bearing in mind...

The radiated heat operates in a different spectrum to that which a black object might otherwise have an advantage. Specifically, a black object might have an advantage in the visible spectrum, but radiation from a radiator is in the infra-red wavelength.

If you paint a radiator black, then some heat from its surroundings may be absorbed by the radiator. But when it comes to emitting heat, I don't think the colour of the paint plays much part. So you're better off with white or whatever colour suits the rest of your room's decoration!

All that before 9am. I think I need a little lie down...

ariba10

It is the same as asking 'What colour overcoat would be warmest?'

beer2006

ariba10 wrote:

It is the same as asking 'What colour overcoat would be warmest?'

No, because if there is sun a black overcoat would be the warmest as it absorbs heat.

I've often wondered this question, I seem to remember a physics teacher at college saying a black radiator would be best, but I've never been sure.

maryjane01

We have been looking at heated towel rails and discovered that white ones are better at conducting heat than chrome one. I don't know why though.

chrisw

I've never really understood why the traditional clothes of some people in hot countries like Greece or Africa are black.

alanobrien

Heat transfer methods = Conduction, Convection and Radiation.

Black is best to absorb heat from an outside source i.e. the sun hence solar panels and industrial heat control equipment are usually painted this colour.

To reflect (radiate) heat you need by definition a highly reflective surface so typically a silver colour is used. Think of the principle of using silver foil behind a radiator to reflect the heat back into the room.

Finally conduction depends on the material the radiator is made from. A steel radiator would conduct heat at a much slower rate than aluminium for instance as it has a lower themal conductivity.

Stompa

http://www.newton.dep.anl.gov/askasci/eng99/eng99320.htm

alanobrien

maryjane01 wrote:

We have been looking at heated towel rails and discovered that white ones are better at conducting heat than chrome one. I don't know why though.

Either the material of manufacture is different (alloy) giving different heat transfer rates or the physical shape or size is different allowing faster flow through or the salesman is good

ariba10

beer2006 wrote:

No, because if there is sun a black overcoat would be the warmest as it absorbs heat.

It is not very often that I wear an overcoat when the sun is out.