When a refrigerator door is left open, the room heats up because the fridge moves heat from its interior to the outside, increasing the overall heat in the room. The refrigerator does not create coldness; it extracts heat from inside and releases it out the back, along with additional heat generated by its machinery. This process results in a net increase in room temperature. Similarly, air conditioning systems function like refrigerators but require external units to dissipate waste heat effectively. Thus, the operation of a refrigerator contributes to warming the surrounding environment when the door is open.