Buying a house with a skylight - and I am thinking about exchanging it with a roof window to open. The skylight is in the highest point of the house, and living, eating, kitchen are connected - this window sits in a chimney-like position. My thought now - we're talking Texas here - heat moves up. If I open the window at night, the warm air from the rooms should easily go out the roof (window) and it should get my AC usage down. Any experience with this?

I think operable skylights cool better in dry climates.  High humidity areas may bring in more water vapor that increases the load on the air conditioning.  Which part of Texas - East, Central or West?