Reheating takes very long, making it a bit of a waiting game, slowing down game-play.
That's not a cost; that's a punishment for playing the game. The player can't control (with accuracy) where the flame will appear plus it seems like more than one flame is summoned when all I wanted was one. Lastly, it seems like the only way to beat the boss is to get close to draw him to you, which leads to him taking away your health (and it takes a large amount of flame to bring him down). I had to recharge myself at least five times. Recharging yourself in the game is basically required to beat it so you are punishing the player for playing your game.