Mustered up the courage to dig (literally) deeper into this. The radiant heating system is indeed copper pipe. As previously mentioned, the material around the pipe came down like sand as I poked my finger into it to get closer to the leak source. So, I'll move forward first by calling in a plumber. However, I'm now curious about the stuff, which looks like sand, falling from the ceiling. I'm more concerned about its ingredients. I've been reading some of the posts related to radiant heating in ceilings and noticed comments about asbestos. Since asbestos was a common building material at the time my house was built (1950s), I'm wondering if the stuff falling from the ceiling may contain asbestos. My husband called me paranoid as I hunted from hardware store to hardware store looking for a testing kit for asbestos. W/two young children, I'd rather be safe (or as my husband calls me "paranoid") than sorry. Can anyone shed some light on what this material may be? Thanks.