Size

• Although the ENERGY STAR program doesn't specify a particular depth for refrigerators, it does specify a total volume. Full-size refrigerators must be at least 7.75 cubic feet, and compact models must be less than 7.75 cubic feet and no more than 36 inches tall.
  
  

Efficiency and Types

• According to ENERGY STAR, certified refrigerators must be at least 20 percent more efficient than nonqualified models. There are a wide variety of configurations available, including single door, compact, and partial- and manual-defrost refrigerators.
  
  

Cost

• Although ENERGY STAR refrigerators may have higher up-front costs than nonqualified models, long-term savings on utility bills may compensate for these higher prices. According to ENERGY STAR, replacing a fridge from the 1980s with a new ENERGY STAR model can save up to $100 each year. Some models may also be eligible for rebates and tax credits.