I have a new-construction home (closed in Oct) that's prewired for ceiling fans. I bought a fan that's ~50 lbs without a light kit. Intending on installing a light kit and then installing the fan, but I'm concerned about that weight being supported by the mount box. I'm pretty sure it's OK, but I also don't want the thing falling on my family. Any suggestions on the max weight that those things are designed to support?
IF the contractor installed boxes designed for hanging ceiling fans you should be fine. A few things you can look for if you're not sure how to recognise a fan box: pre-wired for a fan, metal box (a lot of new construction uses plastic boxes except for fans) but you already had the right suggestion: call and ask! Or the boxes might be (should be) marked so look around on the inside with a flashlight . . .