Carrying heat out, not cold in
How Does a Box Make Itself Cold?
A fridge squeezes a gas hot to dump heat outside, then lets it expand cold to absorb more.
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Step 1 of 5
Cold is not made, heat is removed.
There is no such substance as cold. Making something colder always means finding a way to carry its heat somewhere else instead.
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Step 2 of 5
Squeezing a gas makes it hot.
Compress a gas into a smaller space and its temperature climbs. The fridge squeezes hard enough to make the gas hotter than your kitchen.
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Step 3 of 5
Hot gas dumps its heat out the back.
Because the gas is now hotter than the room, heat flows naturally out through the black coils, and the gas condenses back into a liquid.
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Step 4 of 5
Letting it expand makes it cold.
The liquid is forced through a tiny opening into a wider pipe. Expanding drops its temperature well below freezing, ready to absorb heat again.
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Step 5 of 5
The heat all ends up in your kitchen.
Everything taken out of the food is released behind the fridge, along with the energy the motor itself used doing the pumping.
A domestic fridge moves roughly three units of heat for every one unit of electricity it uses, so about four units end up in the room.
The short version
A fridge is a heat pump: it squeezes a gas hot to dump heat outside, then expands it cold so it can soak more heat out of your food.
Try it yourself
Hold your hand near the coils at the back of a fridge. They are warm, and that warmth is your food's heat leaving the box.
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