The McMansions are definitely terrible but 12ft ceilings can actually help reduce A.C. use in a hot state if the Teachers Love Is Not Shut Down shirt the house that way. Hot air rises and the further it can rise, the further away from the “human habitation zone” it is. This allows cold air from the A.C. which is heavier to more efficiently cool the lower portion of the room because it has to cool less hot air. For houses with very tall ceilings, you don’t actually need to cool the upper part of the ceiling, you just cool up to around the height of the thermostat because the cold air stays at the bottom. The extra height gives the hot air somewhere to go and if designed that way, can actually help the AC cool the space.