Name: Bezz W.
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: December 2002
Question:
Why are most radiators painted white, and not black?
Replies:
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.
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