Well, as this is for a heat mage, the overall potential is much higher than that of a plasma grenade, as he can manipulate it into various forms, ranging from a slung molten bolt of tungsten, to a thermobaric dust cloud.
The maximum temperature should be no higher than 5900, as that is the boiling point of tugsten, which means energy loss from evaporation of metal, so a defense good enough, ceramic for example, will keep this at bay for a while. Also, i plan on having a mana pool, the cost required to generate and manipulate dictated by such parameters as mass and acceleration. Morever, there will be a bottleneck, restricting the amount of force/mass the character can generate per post, widened only by prepping.