Heat output


Postby singer » Wed Jan 21, 2009 2:18 am

Have just been asked to change a bathroom radiator to a towel rail and have been looking at screwfix website.
Can anyone tell me why the same size towel rail in white finish gives a greater Btu output than the chrome finish.
Water temperature will be the same and number of bars on rad is same so why more heat?
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Postby plumbbob » Wed Jan 21, 2009 10:40 pm

Of course it may be the surface area of the white rads is greater than the chromed, but the most logical explanation is the surface finish.

A black surface will radiate a greater volume of heat than a white one. This is text book fact. Very probably white radiates less than chrome.
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Postby Dave From Leeds » Thu Jan 22, 2009 11:13 am

No disrespect plumbbob, but the original poster states that the white one has a higher output than the chrome!
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Postby plumbbob » Fri Jan 23, 2009 12:06 am

Ah, yes, typed that the wrong way round!! Lol.

I meant that chrome will radiate lees than white because it is more reflective. It all works on the same theory as it would in the opposite case where a dark colour absorbs more than white with silver absorbing the least because it reflects the most.

Now have I got it right this time?
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Postby singer » Fri Jan 23, 2009 12:54 am

Now I'm really confused!
Any other thoughts?
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Postby Dave From Leeds » Fri Jan 23, 2009 11:16 pm

Basically, because the white finished rail is less reflective than the chrome one, it will give out more of the heat from the water inside it. This will be compensated by the boiler doing a little bit more work to maintain the water temperature. Hope this helps to clarify the matter.
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Postby singer » Mon Jan 26, 2009 9:54 pm

OK fellas. Thanks for your replies but just so that I know I've got this right(cus I'll have to explain it to the customer)

2 identical chrome towel rails give out the same heat

2 identical towel rails 1 chrome 1 white - white gives out more heat because more heat coming from water inside is reflected back into water because of higher reflection of the chrome on the INSIDE?

So this means if we had 2 identical towel rails with chrome finish and I painted 1 white they would in theory give out the same heat - Am I right?
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Postby Dave From Leeds » Wed Jan 28, 2009 12:35 am

No, it's the external surface finish of the rail that is important. As plumbbob said, a dark colour will be a better absorber than a light one, or in this case the white surface will absorb better than a highly polished chrome one. The actual temperature of both rails after the water inside has transferred heat to them is likely to be the same. However, the white one, being a better absorber will exchange more of its heat energy with cooler air from its surroundings. A matt black finished rail would be even better.
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