I would normally use "mounted on ". I can't think of any case where I would naturally use "mounted to", though I would not say that it is definitely wrong. I don't think I would use "mounted" at all in the case of a fan suspended from the ceiling.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
Guypercan you always use toto sounds wrong to me. on is good.