Priest · Discipline · tier 4 · from level 25

Improved Inner Fire

Rank 3/3

Increases the Armor bonus of your Inner Fire spell by 45% and increases its total charges by 12.

Doesn't change the damage or healing of any Priest spell.

Averages, counting crits and misses, for a level 60 Priest with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.