Your refrigerator and freezer are likely among the highest energy consumption appliances in your home, especially if they are old! However, you can help them run more efficiently by setting an optimal temperature and using them wisely.
In most refrigerators and freezers you have the option to adjust the temperature setting. To make your appliances as energy-efficient as possible, strike a balance between setting the temperature low enough to keep your food fresh and minimize food waste (also a factor in climate change), and high enough to decrease energy consumption.
You can help them run more efficiently by doing a few small things. First, check the seals on the door and ensure the cold is not sneaking out. It is likely fine, but repair as needed.
Second, semi-regularly clean behind and underneath the refrigerator to maintain airflow if you can access them without too much trouble. Most importantly, dust off the coils or filters where the air flows. This helps them run smoother and last longer.
Third, do not under or over-fill your appliance. If you are under-filling, the cold air escapes more quickly when you open the door. Maybe you can downsize to use less energy? On the other hand, overfilling makes it more challenging for air to circulate and cool everything down. For increased efficiency, keep your appliance around three-quarters full.