Air to air heat exchangers move heat energy between two separate air streams. They let two air streams to come into close contact with each other, close enough that the energy can be transferred from one to the other, but not so close that contaminants also transfer. They use a heat pipe to remove heat from an enclosure and release it to the surrounding air. The heat pipe is an evacuated sealed copper tube with aluminum fins that aid in heat transfer. The tube is partially filled with a refrigerant liquid that boils when exposed to the hot air inside the enclosure. The refrigerant liquid boils when it absorbs heat from the hot air, and the resulting vapor goes to the top of the tube where it is condensed by the cooler ambient air as it gives up its heat. It then flows back to the bottom. The process repeats continuously.