We have 11 ft ceilings in our 1 story house in Dallas (current temp: 105). My friend says that higher ceilings result in less A/C usage during the summer compared to 8 ft ceilings (assuming that everything else is the same). His theory is that with high ceilings, the hot air stays up top where you can't feel it (and where it can't trip the t-stat). So the A/C only runs to cool the bottom 6-8 ft of air in the house and the air above that stays warmer. I understand what he's saying, but I think the air is going to mix quite a bit, so while there might be a small temperature difference between the bottom and the top, its not going to be anything substantial (maybe a degree or two). And with higher ceilings, you have a larger air mass to cool, which means more A/C time.
So the question is, if you had two identical houses next to each other with the same insulation, shade, windows, t-stat setting, and A/C system, but one house had higher ceilings, which one would use the A/C more?
We are over in Denton and I have wondered about that same question. Our house has a mixture of 8 ft ceilings(2 bedrooms, kitchen, baths) and vaulted ceilings(peaks at 12 ft in living rm and master bedroom slopes up to 10 ft). I will say the living rm. and the master bedroom are always more comfortable(in the summer) than the 8 ft ceiling bedrooms. The 8 ft celings have more insulation above them, but the warmer air is closer to you than in the higher ceiling areas. The reverse is true in the winter, the eight ft. ceiling areas feel good and the high ceiling areas are a little chilly. But I have wondered if our electric bill would be different if the whole house had only 8 ft. ceilings. We keep our stat at 82 in the summer and at 68 in the winter. If the house had foam insulation and double pane windows, we would probably use very little HVAC, which is our goal.
I'm sure that may play a role, but what you're feeling probably has to do with duct sizing and air volume delivery. My house for example, has 10 to 12 ft ceilings in the game room upstairs, however my daughters 8 ft ceiling room is always cooler.
## + years in the field never made you a know-it-all This industry is far more diverse than you are