So I have a tip to pass on to you folks. It's a strange one, though, involving basements. Finished basements, in particular. Because a basement is underground, it's surprisingly important that the basement be heated and cooled separately from the rest of the house if people are to live there.
The situation we have right now is that my mother-in-law turns into an icicle (not necessarily a bad thing, I'll grant you) when the air conditioning is on in our house. Upstairs in my office, I'm sweltering. Down in the basement she's freezing. The main floor is comfortable. Now we can remove a lot of the heat from the office via the window with a fan, but the basement problem can't be fixed. The fan vents aren't designed to be airtight seals, they push a little less of a cold draught into the already-cold basement. The fan circulating air in the house only slightly ameliorates the problem.