*Ahem, I'm in that game...So normally I would tell you 0, zero, nix, it's not nice to use flamethrowers on people!
But since I'm under obligation here, so I must tell you, that the magician chooses the Force of the spell, witch will have a direct effect on Drain, Damage and the max hits he/she can achieve on the spellcasting test (which is required to hit the person you targeted, since it's a indirect combat spell)