How to Paint an Old Radiator

The homeowner was frantic in his e-mail to me because he had painted a few of his old radiators over the weekend and as soon as the heat came on they smelled carcinogenic. That’s what he said – carcinogenic. “We have a baby!” he wrote. “Can that smell hurt the baby?”

I’d say that’s one of those questions that you should never answer by e-mail, or even in person. I played dumb, which is a good thing to be from time to time. It took me years to learn that.

But his question got me thinking about the right and wrong ways to paint old radiators, so I posed the question to the good people who participate on The Wall (our very-active bulletin at HeaingHelp.com). Here’s what they had to say about their experiences:

John: When customers ask, I tell them to clean the radiator with trisodium phosphate, and then prime it with an alkyd, oil-based primer, followed by a good latex top coat. Sherman Williams and California are two top brands that I have used with good results. Use a brush and hot dog roller. Select a top coat that’s a shade lighter than the color of the wall. Radiators seem to darken after a few heat cycles and then blend with the wall.

Mike: I am a painting contractor and we always use Benjamin Moore Satin Impervo to paint radiators. It is alkyd enamel that sprays well and has a beautiful finish. If we cannot convince the homeowner to remove the radiators so that we can properly paint them in our shop, we are forced to paint the radiators in place. We use either a hot dog roller or a paint brush designed to paint radiators (it’s shaped like a hockey stick and you can find these with a Google search). When painting radiators in place, the oil-based enamel has excellent adhesion to the marginally prepared surfaces. Latex paint is for homeowners.

(So Mike, the professional painter, disagrees with John, the professional heating contractor on whether the top coat should be latex or oil-based. It sounds like they both get good results, though – D.H.)

Thad: Sandblast and powder coat for a couple hundred bucks per radiator and they’ll look brand new. The real trick is to bake them for a bit longer so that any outgassing from the cast iron occurs before the powder coat dries. This will avoid any surface blemishes. I have had seven, 100-year-old steam radiators done this way and they all came out fantastic. And a little bonus is that the finish is so smooth that dust and cat hair don't get stuck in between the sections. It just comes out with a whiskbroom, which I use once a month.

Phil: I sandblasted one myself last fall and painted it with Rustoleum (their bronze metallic finish). The paint went on easily, dried quickly and the radiator looked terrific after painting. It did take a couple of days to finish outgassing once the heat came on, though, so some people will have a problem with that. The paint is somewhat soft, and will get tacky when it is hot (the kids hats and gloves tend to stick when left to dry) and it seems to collect dust and hair. I may try the powder coating method next time, and compare the costs (the do-it-myself solution cost less than $20)

(You get what you pay for. – D.H.)

Mike T.:  I have only painted a few steam radiators, and for most of them, I used plain latex wall paint over an already-sound, painted surface. I saw one batch a few years later, and they were okay, but not great, with a few small areas of rust coming through. I did a couple with traditional, oil-based silver "radiator" paint. The condition of the existing paint (silver) was not too good, but the customer didn't want to go the expense of stripping the old paint. I haven't seen it, but the customer never complained. I haven't yet found anyone willing to pay what I consider a very reasonable fee for one of my custom bronzing jobs.

Tim: I sandblast them and then use an automotive spray gun for the paint. I did use Rustoleum on my first three last year. I had to thin it by half for it to work with the spray gun. I finally bought a compressor to handle the air requirements for the sandblasting before the painting. What a difference!

Kevin: I painted two radiators three years ago with Rustoleum high-heat paint in a spray can. They’re still perfect. The can says the paint can handle up to 1,200 degrees, but there are not a lot of choices when it comes to colors.

Dave: I have radiators sandblasted and powder-coated all the time. They look stunning when they are done. I use a commercial painting company that handles both the blasting and the coating. They have many colors from which to choose. The radiators are cooked at 400-degrees Fahrenheit. It’s important not to get them any hotter than that because the paper gaskets between the radiator sections can be damaged, causing the radiator to leak. Ask me how I know. A large radiator can easily cost as much as $400 for the whole process, plus the time it takes to disconnect, transport to and from the paint shop, and reinstall afterwards. The finish is quite durable, though, and it looks like porcelain.

Patrick: Ditto to everything that's been said about powder-coating. I hate the thought of paying someone else to do what I can do myself with a little sweat and elbow grease, but powder coating is so superior compared to the results I can achieve with even a professional spray setup that I find it's really worth the cost. I've had zero off-gassing issues; the finish is perfect (no drips, drabs, or missed spots), and let's face it – doing a good job of cleaning and painting a radiator of any size is one of the more onerous tasks imaginable. Refinishing radiators seems to me to be a textbook-perfect example of when powder coating makes sense.

Sure sounds to me like power coating wins. Check with a local auto-body shop. They’ll often do this sort of work for you. And I’ve had pros tell me that they’ve taken radiators to monument makers at local cemeteries for sandblasting.

And since I'm not an M.D., I'll pass on the medical questions.

Ray: If the old paint is failing, and was lead based, I would not even remove it without setting up 4-mil plastic sheeting for containment before taking off the piping and wrapping the whole unit in heavy duty plastic and taping it securely before moving. If it had lead paint, I would either bring it to the scrap yard, or pay someone the big bucks to strip it properly. Sand blasting it at home is definitely not the right course of action.