Air conditioning is a great modern convenience. It also happens to use up nearly 1/7th of all the electricity generated in the United States. So it's important to be smart about the way you use it, not just for the sake of the planet, but also for your bottom line.

Start by using a programmable thermostat, which you can buy at any major retailer. Set the AC to turn off about the time you leave for the day, and back on about a half hour before you get home. If you have a wall unit, do the same thing with a plug-in timer.

Set your temperature as close to 78 degrees as possible. Each degree below 78 will increase your energy use by 8%. While the AC is running, close the window shades and shutters, especially on the east and west sides of the house.

Finally, if you're planning to replace your air conditioning system, look for one that's been certified by energystar as efficient models.

Take note of the coolant that's used, the industry standard Freon is being phased out and replaced by the more efficient and earth-friendly Puron.