This can make a huge difference in your comfort. Remember that heat rises and that air moves to equalize pressure. So to clear out hot air, you need to let cool air in somewhere else.
Try A Whole-House Fan
This powerful fan, often built into an attic hatch, pulls air in from open windows and pushes it out through the attic and roof. This is particularly useful in drier climates with hot days and cool nights. The fan is run at night to eliminate the hot air that was trapped inside during the day and pull in the cooler air, reducing the temperature of the house.
Open windows on opposite sides of the room or, if they are all on one side, set up a fan near the opposite wall to direct the air flow. (This is more effective than placing a fan facing outward in the window to swoosh hot air from the room.) If your second story is oppressive while a lower floor is cool, try opening a window downstairs and venting heat as close to the top floor's ceiling as possible -- by opening the top sash of a window, for example. Open windows wider on upper levels than on lower levels to increase air speed and cooling.
Install Ceiling Fans
A fan can make a room feel several degrees cooler. Use one alone, or, if you have central air-conditioning, turn up the thermostat by several degrees when the fan is on. You'll feel just as comfortable and save on cooling costs. (Fans don't actually alter the temperature, so switch them off when leaving the room.) Ceiling fans work best when the blades are seven to nine feet above the floor but no closer than eight inches from the ceiling. Use fans 36 to 44 inches in diameter in rooms up to 225 square feet. For larger rooms, use fans 52 inches or wider. If any room dimension is more than 18 feet, use multiple fans.