I haven't found an answer to this and I can't go to sleep until I do- If two refrigerators are at the same thermostat setting. One empty (assumed regular Earth air inside) and one full of food. Both have already reached the temperature on the thermostat. Which will require more energy to maintain at the set temperature (not specified)? I don't know what equations to use here or if my thoughts are even in the right direction but here goes: It would take more energy to maintain the fridge full of food b/c it has more matter that is subject to reaching equilibrium and so the refrigerator has to actively fight this and costs more energy than the fridge full of air. Hit or Miss?