A refrigerator is an insulated box with a heat pump attached

This is less a set of instructions about refrigeration appliance construction than an argument, and it is worth saying so at the start.

How the cooling actually happens

A refrigerant is compressed, which raises its temperature, and it then releases heat to the room through a condenser coil. Expanding that refrigerant through a restriction drops its pressure and temperature sharply, allowing it to absorb heat inside the cabinet. The compressor is therefore a pump moving heat uphill, and the electricity it consumes ends up as heat released into your kitchen.

This explains why an open refrigerator door does not cool a room and why the appliance warms the space it stands in. It also explains why ventilation around the condenser is not optional, since heat that cannot leave forces the cycle to work harder.

The cabinet and its insulation

Insulation thickness directly controls how much heat leaks back in, and heat leaking in is the entire load the compressor must remove. Better insulation means thicker walls, which for a fixed external size means less usable interior space. Vacuum insulation panels achieve more per millimetre and are more fragile and more expensive, so they appear selectively rather than throughout.

Door seals are part of the insulation system, and a seal that has hardened or distorted admits both heat and moisture continuously. The cabinet is where a manufacturer can quietly save money, because insulation is invisible and its effect appears only on a running cost.

Defrost strategies and their consequences

Moisture entering the cabinet condenses and freezes on the coldest surface, and that ice insulates the very surface meant to absorb heat. Manual defrost designs allow ice to build until you remove it, which keeps humidity higher and requires periodic intervention. Automatic defrost warms the evaporator periodically and drains the melt, which keeps performance steady while cycling the interior temperature slightly.

Frost-free systems circulate air over the evaporator, which removes moisture continuously and therefore dries unwrapped food faster. None of these is simply better; they trade humidity, energy, intervention and food storage behaviour against each other.

Compressors, control and noise

A fixed-speed compressor runs at one output and controls temperature by switching on and off, which produces cycling and audible starts. Variable-speed compressors modulate their output to match the load, which holds temperature more steadily and generally runs quieter. Steadier temperature matters for food storage because repeated warming and cooling cycles degrade texture and shorten storage life.

Compressor and fan noise figures are measured under defined conditions, and the noise you notice is often a resonance in your floor rather than the appliance.

Any refrigerant carries safety and handling rules, and the regulations governing which refrigerants may be used differ by country and change over time.

Air, humidity and where food actually keeps

Cold air is distributed by convection or by a fan, and forced air produces more even temperatures with more moisture loss. Every cabinet has a temperature gradient, and knowing where the coldest and warmest areas are matters more than the average setting. Sealed drawers with their own humidity control exist because different foods need different moisture conditions to keep well.

The measurable part is this: door storage is the warmest position and experiences the largest temperature swings, which makes it the worst place for sensitive items. Food safety guidance on storage temperatures is issued by national authorities and is the appropriate reference rather than any general claim.

What to check before choosing

Measure the space including ventilation clearances and the door swing, since installation constraints eliminate more candidates than specifications do. Compare internal dimensions rather than capacity figures, because insulation and fittings decide what fits. Check whether the door seal is a replaceable part and whether the hinge can be reversed, as both affect long-term usability.

Judged against the category, look at how the interior is subdivided, since fixed shelving and shallow drawers waste more space than a capacity figure reveals. Consider where the appliance will stand, because a warm or unventilated position undoes the efficiency you paid for.

The takeaway

Judge a cooling appliance on its insulation, its seals and where it will stand, not on the number of features inside.

Anything you cannot buy a spare part for is a rental with a long term.