Heat stacks are back-mounted units worn by many Chimera strains, with a few exceptions, to keep their high metabolism rate stable.
Heat stacks are essential for the long-term survival of Chimeran strains, as they are needed to regulate the body temperature due to their high metabolic rate. This Chimeran trait could literally, and fatally, cook the Chimera from the inside out. Heat stacks are surgically grafted in Chimeran strains during the final phase of the conversion process taking place in conversion centers.
In-game, the heat stacks of various Chimera have different effects associated with them, such as the tendency of a Titan's heat stack to catch fire and explode if it suffers enough damage, or a Chameleon's distinctive cooing sound.
- Players can customize the heat stacks of their Chimeran character in online multiplayer in addition to the rest of their appearance.
- Shooting the heat stack of any lower Chimeran strain (such as Hybrids) will explode and kill its user in one shot.
- Heat stacks in certain Chimeran strains can be used for a another purpose, other than preventing overheat. An example of this is the Ravager strain using their heat stacks to generate shields.
- Longgun describes the heat stacks being very vulnerable and can be destroyed by any highly accurate weapons, allowing the Chimera's body temperature to overheat and kill the Chimera.