Well, not to be contrary, but..........
Fans up high should be facing out to exhaust the warm air outside. The warm air inside the coop will be drawn upward by the fan blowing outward from the interior to the exterior. The cooler air flows in from the bottom to replace the warm air pulled...
Well, if it was me, and I wanted to install some ventilation, I think I'd install a regular vent fan to exhaust air to the outside from up high in the coop, and draw cooler fresh air in from below. I recommend using the proper rated fan in this instance. Cheap bathroom fans aren't rated for...