Refrigerators and freezers generally consume more energy than any other single household appliance. Fortunately, refrigerators have become much more efficient in the past 20 years, using 60% less electricity on average than 20-year-old models.

Buying a refrigerator that is larger than you really need, failing to clean refrigerator coils, setting the cooling temperature too low, letting ice build up in the freezer, and poor door seals are some common problems that can increase energy costs. 

Refrigerator/freezer configuration can also affect overall efficiency.  Choosing the least efficient configuration can cost you money.

Best Practices for Increasing Refrigerator and Freezer Efficiency