There is disclosed an inner shoe for a boot such as a ski boot which includes a foot warmer mechanism having a heat engine which includes a compressor, evaporator and condenser coils and interconnecting conduits for circulating a working refrigeration fluid. In a preferred embodiment, the cycle of the heat engine can be reversed, thereby cooling the inner shoe. The mechanism also includes an entirely sealed, remote latch to lock the heat engine out of operation. The inner shoe can have an air system that includes an air bag which surrounds its instep area and communicates to a sealed chamber between the soles of the shoe. The air bag can be pressured to maintain a sense of tightness or security to the ski boot. The air system also augments heat transfer within the boot.