Can I hook up my ceiling fan to the old light box? See situation?

Question

I am hoping to replace my old light with a ceiling fan. I bought a brace intending to use it to support my ceiling fan. However, when I took the old light out, the old light box is nailed to a ceiling joist. So I will be unable to use the brace because the old box is right on the joist.

I though, "no problem", I'll just take the old light box down and put the fan box up. But, the fan box is several inches deep and would hang through the ceiling.

So, my question is, can I hang my fan on the ceiling box?

A friend told me that since it is nailed to the joist it should be plenty stable.

I understand this wouldn't be up to code, but would I still be pretty safe if I used the old light box to hang my fan?

Otherwise, I don't see any other options to hang my fan.

Answer 1

The code is to prevent your heavy ceiling fan from falling and slicing and dicing anyone below.  

If your ceiling box is anchored on the bottom of the joist (not hanging on the side) it should be able to support the weight properly.  Some ceiling fans have additional anchor points that mount into the joist, separate from the electrical box.