Please please please make sure you do NOT plug your 24v DC fan in a socket and let it run. You will not have a happy fan.

I have a 120v fan hooked up in my Red Bull incubator and I did have problems with it heating the incubator up, I eneded up have to run its power through a dimmer switch in order to cut down on its heat generation. I'd stick with the 12V if you can.