No kitchen appliance is capable of making cold. A refrigerator is capable of moving heat, and the direction it moves heat is out of a small insulated box and into the room around it — plus everything its motor consumes on the way. That is why standing in front of an open fridge is such a poor way to cool down.

Eleanor Brackley follows the loop that does the moving. A fluid boils inside the cabinet, because boiling takes heat from whatever is nearest; a pump raises its pressure; the vapour turns back to liquid on coils facing the room, giving that heat up again; and a constriction drops the pressure so the cycle can begin once more. Four parts, one ring, nothing consumed but electricity.

Much of the book is about what the parts cost. The constriction in most household machines is not a valve but a length of narrow tube, sized for a single operating point and unable to respond to anything else — an admission that a machine which cannot adjust but never fails is worth more than one which can. The pump sits inside a steel shell welded shut around its own motor, silent and unrepairable, and the chapter on it explains why sealing the motor in with the refrigerant was the change that made the appliance domestic.

The refrigerant itself is the book's moral centre. What replaced the dangerous early fluids was designed to be inert, and inertness turned out to be the hazard: molecules stable enough to be safe in a kitchen were stable enough to survive all the way to the ozone layer. An international agreement then decided what the industry could put in its machines, and efficiency rules have been redesigning the cabinet ever since — thicker foam, vacuum panels, defrost heaters that run only when needed instead of on a timer.

A final chapter turns the machine around. Reverse which coil faces the room and the same four parts become a heat pump, delivering more warmth to a house than the electricity supplied to it, because most of that warmth was never made — only carried in from outside.

Twenty sources are listed, including patents, museum catalogue entries and the texts of the treaties and standards that shaped the design.