Rule of thumb for electronics is that heat sink should be black if in still air but color doesn't matter very much if air is moving.

Your observations seem to always be true so to "just happen" is probably not correct (but might be).

I don't know the answer but my guess is that when you look at the materials, processes and environment for each the answers will probably show themselves. The home AC radiator is fragile aluminum and probably does not have the fins attached to the tubes containing freon. It might not take road vibration and bumps very well. The car radiator is soldered (copper? brass?), a little stronger than the home radiator and probably needs a coating for corrosion protection. If you have to coat it you might as well use black, especially since there isn't much air moving when the car is stopped.

Just guesswork. It will be interesting to see what someone who knows the answer has to say.

To tell the truth, I sort of think it just happened that way.

It has been awhile since I lived in some New York or Canadian place with the old iron radiators hot from steam.

Most of the time they were up against the wall under the window anyway, so it wasn't like they were going to get much of a boost from sunlight by being black.

And typically, from my experience, women want the inside of the house to look the way they want it to look regardless of any science.

(Hatred of wind turbines in the landscape sometimes reminds me of women who dislike seeing motorcycles in the living room.)

-a guy needs a shed.

As far as car radiators are concerned now they are typically under the hood and behind a grill, and in cold climates early on, having the thing freeze up, was as much a worry as having it boil over.

I imagine it was a wash, and a trade off.

Now you've got me wondering what the first antifreeze coolants were for cars.

Seems like when I was a kid it was simply antifreeze, and then it became antifreeze coolant, and radiators got smaller, and then they even put fans in the mix so you would walk away from your car and hear a fan cooling the engine and wonder if you left the key in it or something.

It might be up there with why so many barns were red.

Red paint was cheapest.

Why are train tracks set the distance apart they are?

They were put to that gauge, according to Henry Petroski, because that was the wheel base of Chariots.

Aluminum, steel or copper will corrode with weather contact. Therefore an anti-corrosive protection is required. Would I buy a car that had green or white sticking out the front? Not likely. Black is mostly cosmetic as any coating will reduce the cooling capacity of the radiator because the paint is an insulator.

Great question. We take some things for granted.

Hi TVP45,

I've done some poking around on the web and combined it with a little radiant heat theory. Though the surface color will contribute to the amount of heat emitted, in the case of the home radiator, there is also natural convection going on. Unless you paint the radiator an ultra matte black, very little variation in heat transfer will be seen as the surface color changes. The choice of silver paint was probably to play on peoples emotion; silver makes the connection in most people's mind as conduction (heat and electrical).

As far as the black radiator in cars, forced convection far outweighs radiant heat-loss, so I don't think color matters much as far as heat transfer is concerned. Plancette had the right idea (to me) that black behind the grille is not noticeable from outside the car.

Good question - made me think!

Mike

Appearance on a car it helps to show off the chrome. The chrome stands out on the black back ground.

I may be wrong but here goes. Several radiators in my house are gold or silver. These seem to heat up more quickly than the one that was painted with grey paint to match the walls. In order to take the paint off I needed to use a torch to burn the paint off. It was thick and had a little rust and peel. Once it was cleaned off I used silver paint in a can (rustoleum). It went on thin and spread evenly and coated well with just one application. It now works as well if not better than the others. Maybe cause it only has one coat.

As far as cars are concerned, I agree with it looks better behind the grill of the car.

Griffin Automotive makes auto radiators (mainly for racing or high performance cars) out of aluminum, and they're left natural color.

Radiative heat transfer doesn't play much of a part with color.