try getting the rad disconnected and drag the sucker outside. You can hose it down or power wash it. Scrape it with a steel scraper, wash it again, Scrape it again, wash it again, you get the picture. Spray prime twice (remember to cover the hole or holes at each end where it was connected to the indoor pipes). Spray insides first. An average rad 34'' HIGH by 24 '' WIDE will take FOUR cans of primer. Don't finish coat till it's in the house re-installed. Don't spray inside unless you have proper vents. Use latex low-luster paint. Don't use Silver paint.. it looks bad... When disconnecting the pipes, be careful for any screens or washers in the pipe, they have to go back! Getting them outside is the trick.. Get all the dirt out!