I will just add, be sure you get exhaust fans which are rated for higher heat. Most off the shelf (e.g. Grainger) fans are rated to 104. In the Texas summers thats too close to ambient for my liking. I use commercial grease fans (restaurants use them) which are rated to 300f. I'd hate for a fan to fail because its summer and then lose the miners because the air cooling stopped. I also put in 3 instead of the 2 I needed (because Im paranoid like that). One set to turn on at 80, another 90, the third 100. The third should never run, but if another fan fails during a heatwave it will.