https://www.diydata.com/information/energy-efficiency/free-energy-savings.php

#3 is interesting...... I wonder if we all do that anyway?

# 6 is very good tip. It said:

"Keep the fridge/freezer full and only put cold food in them. If you don't have enough food to fill a fridge, put plastic bottles filled with water in it. (Every time the door of an upright fridge/freezer is opened, cold air rushes out, keeping the fridge/freezer full reduces the cold air which can rush out)."

In another word, full refrigerator is an efficient refrigerator.

I wonder if the more full it is,the harder it is for it to keep the temp??