I live in the desert and my outdoor flower room has an a/c unit which doesn't work for shit unless I forcibly exhaust the heat. (vent is tword the top of the shed, fan forced) Heat rises, so little worry of venting-out the cooler air.
Easily a 10-20 degree difference between vent open, and vent closed. Also...after watering, the humidity skyrockets without the exhaust.