I'm convinced that outwards is the most effective in this scenario: Open your bedroom windows on a cool spring/summer night. On the opposite end of the house,

I'm convinced that outwards is the most effective in this scenario: Open your bedroom windows on a cool spring/summer night. On the opposite end of the house, put a fan in a window blowing outwards. This cools the entire house, giving your bedroom the freshest air. In the morning, close all the windows. This leaves the house cooled and drastically reduces your A/C usage. Blowing inward doesn't have the same effect of pulling air through the whole house.