If you're selling your house during the summer, you might want to replace dark-colored decorations with furnishings that are lighter in color and weight. Tthat will help open up and lighten a room. You can also decorate your fireplace for the summer by removing the grate from inside the fireplace and replacing it with a fireplace candelabrum or several individual candles. The incandescence will provide a wonderful ambience without turning up the heat.
You can als install dimmer switches to add ambience. They cut down on energy and unwanted heat. Another tip is to use low-wattage light bulbs whenever possible.