Question

If the door of a refrigerator is kept open in a room, will it make the room warm or cool?

Answer 1

A fridge can be though of as a "heat pump". It takes air inside the fridge and cools it by removing heat from it. This heat has to go somewhere, though, and is usually blown out the back of the fridge by a little fan. (If you feel the back of a fridge on the outside it will usually be warm if the unit is running).

For this reason, when a fridge is running it is really warming up the room a little bit. In fact, since we can’t design a fridge to be perfectly efficient (the 2nd law of thermodynamics guarantees this), some of the electrical energy gets converted to heat, so more heat gets dumped outside the fridge than gets pumped out, so even if you open the fridge door to let the cool air escape the fridge will still be heating the room more than cooling it.