On Heroic difficulty, the second and third Felfire Crushers are replaced by Felfire Demolishers. An updated Siege Weapon schedule can be found in the table to the right.
Note that Siege Nova does not deal damage to the Hellfire Cannons - only to the raid. These Siege Weapons can thus be deprioritized if other, more important targets are active at the time, such as a Gorefiend Terror.
Additionally, the Contracted Engineers gain a new ability, Repair, that will channel a healing beam on a nearby injured Siege Weapon. Players must interrupt the channel to ensure they can kill the Siege Weapons quickly and minimize damage to the Hellfire Cannons.
Finally, 28 shots - or 7 boxes of Felfire Munitions - are required to break down the Reinforced Hellfire Door on Heroic difficulty.