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Name: Bezz W.
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: December 2002

Why are most radiators painted white, and not black?

Very thoughtful question. As your question implies, a black radiator emits heat much more readily than a white one, just as it absorbs heat incident on it efficiently. The reason for the white coloring is certainly a cosmetic one -- in most settings a white radiator is considered esthetically more pleasing.

This could be an important effect if radiation were the only means of the radiator transferring heat energy to the room. A radiator with emissicity of 1 (a black body) at 350 Kelvin (77 Celsius = 170 Fahrenheit) emits as much heat as a radiator with an emissivity of 0.2 at a temperature of 523 K = 250 C = 482 F. So a white radiator would have to be dangerously hot to compete with a black radiator.

However, heat is also transferred to the room by conduction to the air touching the radiator, which is the main transfer process and is independent of the color of the radiator.

Best, Dick Plano

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