The refrigerator is one of the biggest users of energy in most homes because it's on 24 hours a day, seven days a week. It isn't practical to unplug and replug it in to save energy, so do the next best thing: Set your fridge to 40 degrees. Forty degrees is the optimal temperature to keep perishable foods safe from growing harmful bacteria. If you set it any warmer, your food could become an unhealthy breeding ground. Fill empty jugs with cold tap water and place them inside. The chill of the cold water will help keep the interior temperature cold, saving energy in the long run.