Open the fridge and a wave of cool air greets you. It is easy to imagine that the fridge is making cold, but that is not really what happens. A fridge is better described as a heat mover. It takes heat from inside the box and pushes it out into your kitchen. Understanding how it does this makes a few everyday habits suddenly make sense.

Heat naturally flows from warm to cool

Heat always moves on its own from warmer things to cooler things. A hot drink cools down because heat flows into the cooler room around it. A fridge needs to do the opposite: move heat from the cool inside to the warmer room. That takes energy, which is why a fridge needs electricity.

The key ingredient: a refrigerant

Inside the pipes of a fridge is a special fluid called a refrigerant. It is chosen because it changes between liquid and gas at useful temperatures and pressures.

The trick relies on a simple fact you have already experienced. When a liquid evaporates, it absorbs heat from its surroundings. That is why you feel cool when you step out of a swimming pool or shower. The water evaporating from your skin takes heat with it.

When a gas condenses back into a liquid, the opposite happens. It releases heat.

A fridge uses this pair of effects in a continuous loop.

The cooling cycle, step by step

The cycle has four main parts.

  1. The evaporator. Inside the fridge, the refrigerant flows through coils as a cold, low pressure liquid. It evaporates into a gas, absorbing heat from the air and food inside. This is what cools the fridge.
  2. The compressor. The gas then travels to the compressor, usually at the bottom back of the fridge. The compressor squeezes the gas, raising its pressure and temperature. This is the part you sometimes hear humming.
  3. The condenser. The hot, high pressure gas moves through coils on the back or sides of the fridge. Here it releases heat into the room and condenses back into a liquid.
  4. The expansion valve. The liquid then passes through a narrow opening that lowers its pressure. That makes it very cold again, ready to return to the evaporator and absorb more heat.

Then the loop repeats.

Why the outside gets warm

If you have ever touched the side or back of a fridge and felt warmth, now you know why. That is the heat being released from inside the fridge, plus some heat from the compressor's work. The fridge is literally moving heat out into your kitchen.

The thermostat keeps it steady

A thermostat checks the temperature inside. When it gets too warm, the compressor switches on and the cycle runs. When the target temperature is reached, it switches off. That is why a fridge seems to turn on and off throughout the day.

Food safety agencies in many countries recommend a fridge temperature of around 5 degrees Celsius or below. It is worth checking the guidance where you live and the manual for your fridge.

Habits that help your fridge work well

Knowing how a fridge works explains some simple advice.

  • Leave space around it. The condenser needs to release heat into the room. If the fridge is squeezed tightly against a wall or cupboards, that heat has nowhere to go. Check the manual for recommended gaps.
  • Keep the door closed. Every time you open it, warm air rushes in and the fridge has to work to remove that heat.
  • Let hot food cool a little first, following food safety guidance, rather than putting very hot dishes straight in.
  • Do not overpack it. Cold air needs to circulate around the food.
  • Keep the coils clean. Dust on the condenser coils can make it harder for the fridge to release heat. Check your manual for how to clean them safely.
  • Check the door seal. A worn seal lets warm air in.

Freezers work the same way

A freezer uses the same cycle, just set to reach a lower temperature. Many fridge freezers share one cooling system, with air directed between the two sections.

The takeaway

A fridge does not make cold. It moves heat from the inside to the outside using a refrigerant that absorbs heat as it evaporates and releases it as it condenses. Give it room to breathe and keep the door closed, and it can do that job efficiently.