I've looked and haven't found one but before I give up, I'm wondering if anyone makes a 4" square fan rated box? The reason I ask is the neighbor has a old fan in his garage hanging from an ordinary 4" steel box and the fan needs to be replaced. I mentioned that it might be a good idea if he used a fan rated box. One little problem, the current box has 3 pieces of conduit going into it. One from the top and two from the sides, so it would be a lot easier if everything lined up nice and neat.