How does a refrigerator keep things cold inside?
In fact, a refrigerator does not carry cold. It carries heat.A refrigerator does not make cold air. It keeps things cold by carrying heat from inside to the outside. A substance called a refrigerant flows through pipes: it takes in heat as it evaporates inside the fridge, and gives that heat off to the room as it is squeezed and turns back into a liquid outside. This repeats again and again.
The same idea as sprinkling water
When you sprinkle water on the ground in summer, the air around it feels cooler. That is because water takes heat from its surroundings as it evaporates, which is called the heat of vaporization. According to Japan's Ministry of the Environment, refrigerators use the same principle. Of course, you can't spray water inside a fridge, so a substance called a refrigerant circulates through the cooling machinery and carries heat.
How the refrigerant carries heat
According to a physics guide from Georgia State University in the US, a refrigerator lowers and raises the refrigerant's pressure so that it evaporates and condenses (turns from a gas back into a liquid) in turn. The low-pressure liquid refrigerant evaporates in pipes inside the fridge, taking heat from the inside as it does. The refrigerant, now a gas, is squeezed by a compressor, and as it turns back into a liquid in pipes on the outside of the fridge, it gives off the heat it carried into the room.
Why the back of a fridge feels warm
If you hold your hand near the back of a running refrigerator, it can feel warmer than the room. That is because the fridge is dumping the heat it collected from inside into the room. On its own, heat only flows from warmer places to colder ones, but a refrigerator uses electricity to run its machinery and pump heat from the cold inside to the warmer outside. Air conditioners work the same way.
How refrigerants have changed
For a long time, substances called fluorocarbons were used as refrigerants. Some fluorocarbons damage the ozone layer, and others strongly add to global warming, so their use has been gradually restricted. According to Japan's Ministry of the Environment, Japan ended production of the types of fluorocarbons that damage the ozone layer by 2020. Today, more and more home refrigerators use a refrigerant made from isobutane, a substance that occurs naturally.
Want to know more?
- Japan's Agency for Natural Resources and Energy estimates that going from a fully packed fridge to a half-full one saves 43.84 kWh of electricity a year.
- Putting hot food such as curry or soup straight in raises the temperature inside and uses extra electricity, so it is best to let it cool first.
- One fluorocarbon commonly used in air conditioners and refrigeration equipment warms the Earth about 2000 times as much as carbon dioxide.
Quick quiz: test yourself
How does a refrigerator cool its inside?
Show the answer
- It carries heat from inside to outside
- It makes cold air and blows it in
- It makes ice to cool the inside
It carries heat from inside to outside A refrigerant in the pipes takes in heat as it evaporates inside, then gives that heat off to the room as it turns back into a liquid outside.
A refrigerant in the pipes takes in heat as it evaporates inside, then gives that heat off to the room as it turns back into a liquid outside.
Next quiz ›Sources
- Refrigerator / Heat Flow to Hotter Region (HyperPhysics)Georgia State University（アメリカのジョージア州立大学、物理学の解説）
- 自然冷媒について環境省 自然冷媒普及促進サイト (in Japanese)
- 家庭でできる省エネ（キッチン）資源エネルギー庁 省エネポータルサイト (in Japanese)
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
