That would depend on what your innards/heatware actually is/are. Then we will also need to know what you're currently working with(make and model of the current case and innards) and the case you want to buy in the hopes of improving airflow so we have a comparison.
Also, as a thumb rule, think of a case as a room with no windows or ventilation and no air conditioning, plonking a ceiling fan won't do anything to deal with the heat inside the room if you were in it. If you added a couple of windows and allowed cross ventilation, then yes the temps would drop.