Most people don't think of their refrigerator as being a big contributor to the home's energy bill, but in fact it is the third largest energy consumer in most homes, right behind space conditioning, and water heating. They usually represent between 6 and 16 percent of a home's total energy cost.

Like air conditioners, refrigerators and freezers use the vapor- compression cycle to remove heat from inside the appliance and exhaust it into the surrounding air.

Today's refrigerators are more efficient than older models. Improvements have been made throughout the appliance from better door seals and more insulation to more advanced controls, motors, and compressors. As a result, refrigerators with 15 to 20 percent higher efficiencies are available and may be cost effective depending on the utility rates.

In recent years, the “smart refrigerator” has become more prevalent in the market place. These refrigerators are now some of the most energy efficient that you can buy. Most models are enabled with color monitors and Wi-Fi, while some include analytics that can anticipate the homeowner’s behavior. There are mobile applications that connect a mobile device to the refrigerator allowing for easier grocery shopping or even leaving messages on the display. It is likely that “smart refrigerators” will be seen in more and more households over the next few years.

When shopping for a new unit, be sure to look for EnergyGuide labels to see how many kilowatt-hours (kWh) the refrigerator or freezer will use in one year, and compare models based on these figures. Energy consumption varies widely between models and companies so it's worth checking closely. Paying a little more for a unit that costs less to operate may be one of the best investments you can make. When shopping, look for EnergyStar labeled units which exceed federal efficiency standards by at least 20%.

Refrigerators with freezers on top are more efficient than those with freezers on the side. And chest-type freezers are 10 to 25 percent more efficient than upright cabinet models. This is partly because they are better insulated, and partly because they don't allow air to pour out when the door is opened. Also look for good strong door hinges that create a good door seal.

When you replace your refrigerator or freezer, check with your utility to see if they offer any rebates for upgrading to a more efficient model. And be sure to dispose of the old unit properly. See if the store where you purchase your new unit will haul it away. If you must put it out for solid waste pick up, remove the door. Children might be tempted to play inside and can be trapped if the door is left on.

Finally, resist the temptation to repurpose it in the garage or basement as a soda fridge. Doing this effectively eliminates all savings obtained in the new unit. They have poor efficiency already, their seals may be worn out (see below), and the space is likely unconditioned causing the unit to run more. It can be a huge hit to the electric bill.

Living with the current unit a bit longer

Short of replacing your current refrigerator or freezer, there are plenty of improvements you can make to your existing unit. First, check door gaskets to be sure they are sealing properly. As they age and wear, they are less able to do their job of keeping cool air in and warm room air out. This requires the unit to run unnecessarily, wasting energy.

There is a simple test to see if your seals are working properly. Place a slip of paper or dollar bill on the edge of the unit, close the door, and pull on the paper. If it slips right out, the seal should be considered for repair or replacement. (If your door seals are magnetic, the test may not work.) Replacing door seals can get expensive, and if your unit is older anyway, it may be time to look at upgrading to a new energy- efficient model.

Check the inside temperature of your refrigerators and freezers with a thermometer because the ones built in aren't always accurate. A setting 10 degrees lower than recommended can raise operating costs by 25 percent. The refrigerator compartment should be between 36°F and 38°F, and the freezer, between 0°F and 5°F.

Regular maintenance of refrigerators and freezers includes making sure heat exchange coils are kept clean and have good air flow.

A full refrigerator or freezer operates more efficiently than an empty one. This is because when the door does open, if it is full, there isn't much area where warm air can enter. You can fill empty spaces with containers of water, which in a freezer has the added advantage of being able to hold a lower temperature in the event of a power outage.

Food should be covered prior to being placed in a refrigerator or freezer. Uncovered, moisture in the food will be evaporated into the interior of the unit causing it to use more energy. And don't put hot food directly into the refrigerator or freezer. Let it cool a little first, but don't leave food standing around too long either because bacteria grows well in unrefrigerated food.