Heat Amplifiers aren't very useful at the moment, as items frequently stop gaining heat until players can afford the Fire Crystal cost, and extra heat does not carry over to the next level.
A 10% or so reduction in Fire Crystal requirements to use the Forge while a Heat Amplifier is active would make the item much more desirable.
stating idea again.
to me, every [instert amount here] of heat should give a 1% chance of upgrading the item. high level forge would funcion as multipliers. that would give sense to the huge amount of fire crystals required in higher levels.