The heavy incinerator is essentially a napalm launcher; it lobs flammable fuel with a splash damage possibility at the target in an arc. These 'projectiles' cause splash damage, and will most often set the enemy on fire, unless a large 'miss' variance is registered. The heavy incinerator can be fired at extremely long distances with relatively good accuracy; it can even be effectively fired across the Potomac River to hit enemies on the other side.
Just having the heavy incinerator equipped is enough to ignite gas leaks because of the pilot light on the front of the weapon.
The appearance of the heavy incinerator is closer to that of the original flamer from Fallout than the flamer from Fallout 3.
During the reloading animation, the small handles on the fuel tanks all start to turn and then stop when the weapon is loaded.
The fuel tanks on the sides are almost identical to flamer fuel canisters including the small handle on the top of the canisters, this proves that the incinerator fires bolts of fuel instead of lit canisters.