Painting Heating Radiators

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Dear NH,
My situation is pretty basic. I am remodeling a farm house that was originally built in 1885. The house is heated with a one pipe steam radiator system that was originally coal - converted to oil first and now to gas. I have 8 beautiful radiators that are being stripped of the some dozen coats of paint by sand blasting with oxidized aluminum. 2 of then are done now and the detail is incredible! And with the paint gone the heat efficiency is so much better.

My question comes down to this. Do I need to coat them with anything for protection of the cast iron? If so, what do I use? I am having a heck of a time finding this answer. I have heard everything from Jet engine paint to cooking oil! Any advise will be greatly appreciated.
JR from Lansing, Michigan

Yes, you should coat them. The overall appearance is better, cleaning is easier, they will be protected from rust, and you can use the paint to control the heat they radiate. If you use any type of oil, such a cooking oil, you may protect the iron from rust, but you will also make future painting very difficult if not impossible, attract dust to the residual tack from the oil, and in general make their appearance less attractive.

You may use polyurethane if you want a clear coat. The best finish by far is a sprayed paint for durability and consistent appearance. A high temperature paint can be used, but it is not absolutely necessary. The temperature of steam is within the working range of most spray paints. Don't use a latex spray. It will not provide a tough enough finish. A gloss oil is the best.

Choosing the color is critical to control the heat output. If you paint the radiators black, they will generate much more heat than if you paint them white, "natural" silver or gray. I learned this years ago during the 1970's oil crisis, when solar heating and cooling was the "in" thing. I don't remember the specific scientific reasons, but darker surfaces both absorb and radiate heat better than lighter surfaces.

I remember making a mistake with radiator color in my first home, which had a similar steam system to yours. There was one bathroom in the house that had you sitting inches from the radiator. Anyway, I thought it would be aesthetically pleasing (read "look cool") to paint the radiator black. Well, the BTU output from this tiny radiator was so intense that I ended up repainting it white to make the room useable. After that, I selectively repainted radiators black or white based on my heating experience in each room. Since most of the radiators were under covers, the color change was not noticeable, but the temperature difference sure was! BTW, if you install a reflective metal shield behind each radiator, either aluminum or sheet metal, you will also increase the amount of heat radiated back into the room. Again, aesthetics rule.

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