Heat stacks are back-mounted units worn by many Chimera strains, with a few exceptions.
Heat stacks are essential for the long-term survival of Chimeran strains, as they are needed to regulate body temperature due to their high metabolic rate. This Chimeran trait could literally cook the Chimera from the inside out.
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.
- According to Rachel Parker's narration, Sergeant Nathan Hale briefly wintess the cooling apparatus with the heat stacks attached to a Hybrid's back in the birthing chamber during the final phase of the conversion process while he escape from Grimsby with Parker.
- Players can customize the heat stacks of their Chimeran character in the Resistance 2 online multiplayer in addition to the rest of their appearance.
- Shooting the heat stack of any lower Chimeran strain (such as Hybrids and Advanced Hybrids) Will kill them 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 as well as to prevent them from overheating.
- 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.