Furnace within is a spell from Races of Eberron that comes with a certain 'mindset'. This means that as long as a wizard (or other prepared caster that can cast this spell) has this spell prepared, they benefit from a certain bonus. In the case of Furnace Within, this bonus is as follows:
Mindset: The energies you manipulate while preparing this spell cause an intense heat to well up within you. Although it doesn't harm you, this heat makes your unarmed strikes, natural weapon attacks, and melee attacks with metallic weapons deal 1 point of fire damage in addition to their normal damage. This heat dissipates when the spell is cast.
If a Wizard has this spell prepared multiple times, would this bonus stack? And would this bonus stack with other things that grant extra fire damage to a weapon, such as a crystal of energy assault?