[JP]

Heatsinks on your computer work similarly, and they're quite effective.  Mostly, they're left with a metal surface, which means the designer isn't particularly worried about the low radiation efficiency.

Also, if you check out the wiki link on radiators, they say what most of us are saying: they don't get hot enough to heat efficiently by radiation. 
http://en.wikipedia.org/wiki/Radiator_(heating)

If you've ever shopped for space heaters, though, you'll find they do get hot enough to radiate, and many of them are designed specifically with reflectors to "beam" the heat in one direction.  If you've ever used one of these, you can actually feel the difference between getting in the path of the heat radiation and just standing near it and being heated by convection.

[CZARCAR]

efficiency aint @ the radiator, its @ the furnace so the rad is filled with hot water & disconnected. Q= which color will heat the room quicker & 2=whch color will heat the room more efficiently BONUS Q= why?

[damocles]

If you disconnect the radiator and leave it with hot water in it, and presume, for simplification purposes only, that the room has no heat losses, then
Q1: Visible emissivity (= colour) will make no difference. If IR emissivity is the same for all cases then any colour will heat the room equally fast.
Q2: Any colour will heat the room equally efficiently because the total heat content of the room is fixed, and the eventual result is a radiator at room temperature, and a room temperature slightly higher than it otherwise would be because of the quantity of heat stored in the radiator (which does not vary with colour).
BONUS Q:  I hope has been adequately answered with the explanations attached to the other questions.

[CZARCAR]

 Kirchoff? room nonheatloss is unrealistic

[Geezer]

I propose a second experiment: We suck all the air out of CZARCAR's kitchen to see if his fridge still works. We could put the fridge into orbit instead, but it might be a bit difficult to find a long enough extension cord.

[CZARCAR]

I propose a second experiment: We suck all the air out of CZARCAR's kitchen to see if his fridge still works. We could put the fridge into orbit instead, but it might be a bit difficult to find a long enough extension cord.

need 2 cords= i have a small chest freezer with matching coluors

[neilep (OP)]

I propose a second experiment: We suck all the air out of CZARCAR's kitchen to see if his fridge still works. We could put the fridge into orbit instead, but it might be a bit difficult to find a long enough extension cord.

need 2 cords= i have a small chest freezer with matching coluors

I have a spare power cord..it's very long....about 15 metres !...so..that's half the problem solved already !


THANK YOU ALL for the great replies here...it makes for very interesting reading..I am learning a lot...



Thanks again.

[Bored chemist]

If you disconnect the radiator and leave it with hot water in it, and presume, for simplification purposes only, that the room has no heat losses, then
Q1: Visible emissivity (= colour) will make no difference. If IR emissivity is the same for all cases then any colour will heat the room equally fast.
Q2: Any colour will heat the room equally efficiently because the total heat content of the room is fixed, and the eventual result is a radiator at room temperature, and a room temperature slightly higher than it otherwise would be because of the quantity of heat stored in the radiator (which does not vary with colour).
BONUS Q:  I hope has been adequately answered with the explanations attached to the other questions.

Eventually, the room will reach the same temperature, but it will do it faster with a black radiator than with a silver one.
The point about radiators is power transfer, not energy.

The interesting point is that, because of the way our eyes are made, we cannot tell a black radiator from a white one.

[Don_1]

Most interesting replies, but all very wrong.

I know exactly why radiators are white, its quite simply so that 'er indoors can regularly tell me to repaint them because they have gone off colour. White shows up this fenom phenon phonen phenonimum phenominum phenomenon better than any other, even with the best paint, which usually smells of formaldehyde. If anything needs preserving around here, its me, not the bloody radiator.

[Geezer]

Most interesting replies, but all very wrong.

I know exactly why radiators are white, its quite simply so that 'er indoors can regularly tell me to repaint them because they have gone off colour. White shows up this fenom phenon phonen phenonimum phenominum phenomenon better than any other, even with the best paint, which usually smells of formaldehyde. If anything needs preserving around here, its me, not the bloody radiator.

I have a great excuse scientific reason why you should not do that Don. The reason Mrs Don_1 is always telling you to turn up the thermostat is because all the layers of paint on your radiators are preventing the heat from getting out of the bleed things. They work mainly by conduction, and paint is not a very good conductor (unless it's loaded with heavy metals like lead and stuff), so the more paint you put on them, the less effective they are at heating your house.

Soooooo, what you should really do is strip all the paint off, and give them a spray with some acid, or even salt water, so they develop that nice dull iron-oxide finish that seems to be quite popular with the arty crowd these days.

[Don_1]

Strange you should say that Geezer, I keep telling the silly old bat that if I paint the walls much more, there'll be no space in the rooms for us to get in!