Cast Iron Radiators

bobbob

Okay, so black dissipates heat best. How about other dark colors--such as navy blue or deep deep red, or battleship gray? Would there be a significant difference? I would like to paint all my radiators a different wild deep color.

Jamie Hall

Go ahead. Pretty much any paint colour you want to use will work, provided that it isn't a metallic like silver (grey is fine, silver isn't) or bronze (various browns are fine). It's the metal flakes that are the problem.

bobbob

The question I still have is this: Is black SIGNIFICANTLY more efficient at dissipating heat than say, navy blue, or any other non-metallic deep dark color. I know many motorcycle manufacturers paint the cylinders black to enhance heat dissipation on air-cooled engines. Harley used to sell a very popular "wrinkle black" paint that I often used.
I want my system to work at maximum efficiency, but would like to paint my rads some colors other than black.

retiredguy

If you are looking for the best efficiency, have all the rads sand blasted and don't paint them.

Jamie Hall

bobbob said:

The question I still have is this: Is black SIGNIFICANTLY more efficient at dissipating heat than say, navy blue, or any other non-metallic deep dark color. I know many motorcycle manufacturers paint the cylinders black to enhance heat dissipation on air-cooled engines. Harley used to sell a very popular "wrinkle black" paint that I often used.
I want my system to work at maximum efficiency, but would like to paint my rads some colors other than black.

No. Any flat, non-metallic paint will have very nearly the same emissivity as any other flat, non-metallic paint. The motorcycle folks do that because it looks cool (or whatever the current term is). In an aircooled engine, it can actually raise cylinder head temperatures. The aircraft folks, who really do have to worry about cooling, don't paint the cylinder heads and barrels at all.

ChrisJ

Jamie Hall said:

bobbob said:

The question I still have is this: Is black SIGNIFICANTLY more efficient at dissipating heat than say, navy blue, or any other non-metallic deep dark color. I know many motorcycle manufacturers paint the cylinders black to enhance heat dissipation on air-cooled engines. Harley used to sell a very popular "wrinkle black" paint that I often used.
I want my system to work at maximum efficiency, but would like to paint my rads some colors other than black.

No. Any flat, non-metallic paint will have very nearly the same emissivity as any other flat, non-metallic paint. The motorcycle folks do that because it looks cool (or whatever the current term is). In an aircooled engine, it can actually raise cylinder head temperatures. The aircraft folks, who really do have to worry about cooling, don't paint the cylinder heads and barrels at all.

Aircraft engines have a huge prop to cool them.
Motorcycles have nothing other than a breeze if they're moving. Personally I feel motorcycles have the disadvantage in that regard.


For what it's worth though :

Lighter colors and also whites and metallic substances absorb less of the illuminating light, and as a result heat up less; but otherwise color makes little difference as regards heat transfer between an object at everyday temperatures and its surroundings, since the dominant emitted wavelengths are nowhere near the visible spectrum, but rather in the far infrared. Emissivities at those wavelengths are largely unrelated to visual emissivities (visible colors); in the far infra-red, most objects have high emissivities. Thus, except in sunlight, the color of clothing makes little difference as regards warmth; likewise, paint color of houses makes little difference to warmth except when the painted part is sunlit.

The main exception to this is shiny metal surfaces, which have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft.

From : https://en.wikipedia.org/wiki/Thermal_radiation

bobbob

Thanks much!

Sal Santamaura

The complete story, previously provided by Dan, as usual:

https://heatinghelp.com/heating-museum/does-the-color-of-a-radiator-matter/

Click the link at the end of that article.

mattmia2

To get back to the original question, this is the last thing you should be thinking about if your concern is efficiency. Match the boiler to the system. Fix venting issues and issues with steam and water getting places they shouldn't be. Insulate the steam piping. Insulate and air seal the structure. Keep the pressure in the system low. Dont use radiator covers or if you do design them to help not hurt output.

bobbob

1. I am talking about my existing system. There is nothing I can do to match my boiler to the system
2. I am fixing venting issues
3. I have insulated my pipes
4. I have long ago done everything I could to air seal my home
5. System pressure is low
6. I got rid of the radiator covers
7. The only thing left is dealing with the colors I want to paint my 12 radiators.

Appreciate all the responses. BTW, the article I was referred to by Sal helped me to understand a couple things about my system: It would appear that the present boiler is not original to the house because the near boiler piping is black and appears newer. The older piping was painted silver--apparently to minimize heat loss from not being insulated. I just had figured that they were painted to deter rust, and that silver (aluminum) paint was what they had lying around. Seems more likely to me now that a previous owner may not have been able to afford insulating and did what they could to reduce heat loss through the pipes. Whatever...