Full vs Empty Refrigerator Tested

My custom painted 1982 Rangaire fridge

I've always heard that a full fridge will use less energy to run than an empty one. I've always believed this to be true, thinking that the cold food would act like a cooler, and make it stay colder longer. After doing a quick Google search, I found that the answer to this question was often disagreed upon and I couldn't find a definitive answer. After filling my fridge with several gallons of water to take up empty space, I decided I wanted to answer this question once and for all, and see if I was actually saving energy. I thought about testing this somehow, and I wanted to do it right. I set up a basic experiment and I feel anyone could replicate this for themselves.

My objective

The main reason I wanted to know this answer wasn't because of my kitchen fridge, but because I have an old 1982 Rangaire fridge in the basement that I use as extra space when my main one is too full. Because of this, I don't keep a whole lot in it, besides some extra frozen meats, and of course cold beer. This fridge was also perfect to do my test, because I really didn't feel like completely emptying my main fridge.

Setting up the test

To do test, I need to find a way to measure the amount of energy. Since I didn't have a way to measure how many watts I was actually using off hand, I decided to just measure the amount of time the fridge took in between running as well as the amount of time it kicked in. I started by filling up the fridge with jugs and bottles of water, but leaving enough room for good air circulation. I allowed the fridge to sit overnight, so that the water would be the same temperature as the air in the fridge. I then waited for the fridge to stop its running cycle and starting the time for one hour, keeping track of the cycles. I then completely emptied the fridge and let it do its thing for a few hours before starting the next test. I tested the empty fridge exactly the same way.

Full fridge

The Results

Through the experiments, I found that the fridge cycled on and off pretty consistently, making it very easy to
measure and compare.

The full fridge

Over the period of an hour, the full fridge would sit for about 13 - 14 minutes, and ran for about 5 minutes. The fridge kicked on 3 times for a total of 14 minutes, 48 seconds.

The empty fridge

Empty fridge

The empty fridge would run for the same 5 minutes, but ended sitting for a full 19 - 20 minutes. The fridge only kicked on twice over an hour, for a total of 10 minutes even.

But wait there's more...

After each test, I also wanted to see if there was a difference when opening the door. To do this I waited for the on cycle to end, then opened to door for 30 seconds, and repeating the same tests. Although causing the fridge to kick on much sooner, the results remained the same, with the cycles returning back to normal in just over an hour. Surprised with the results, I decided to do one more test. Some things I read online said to just use jugs that were filled with air only. The thought is that air is easier to cool and when you open the door, there will be less air that can fall out. I tested this with the door closed first and then the door open for 30 seconds. The results were much better than the water test, but still fell 1 - 2 minutes behind the empty fridge.

Conclusion

I was shocked by the results, but after knowing them, came up with an explanation of why this happened. Basically, the jugs of water in the fridge absorb the cold air, causing the air in the fridge to warm up faster. Unfortunately, trying to save energy by filling your fridge just doesn't work. In a real world situation you'd be even worse off because it wouldn't be empty vs. full, but instead somewhere in between vs. full, and the energy difference would be minimal. Results will vary between all refrigerators, and may even make less difference with side by sides and freezer on the bottom models. But in general, you will find that the empty fridge wins.