Greater Heal (Rank 7)
825 Mana, 40 yd range
3 sec cast
A slow casting spell that heals a single target for 2396 to 2784.
As you can see, Greater Heal is a rather slow spell but it packs a punch.
Nearly every priest dedicated to healing has 5 talent points invested into Divine Fury. So the effective casting time of your Greater Heal will be 2.5 seconds, not 3.
This is still quite some time. Many bosses hit your tank more than once in 2.5 seconds. So you have to be careful about using this spell. It is however far from useless.
Greater Heal has both, the highest Health per Mana and the highest Health per Second rate of all your healing spells. Prayer of Mending is capable of topping this i think, but this is very situational and involves more than one person taking damage.
So, Greater Heal is the bread and butter spell if you want to heal a lot of damage over a long time.
Greater Heal has a long casting time and due to this a rather large probability to overheal if you are not careful. It is very inflexible and allows no quick switching of targets or fast adaption to alternating circumstances.
When & how to use
Use your Greater Heal when you are healing one target that will take a lot of damage and will continue to do so for, at least, the next couple of seconds. If your target is not taking damage at a constant rate, be sure to cancel your Greater Heal halfway through if your target is still topped off, or nearly so. Then start casting your heal again. This is the case for most tanks, so spam your Greater Heal if you are healing your main tank.
When not to use
Don’t bother with Greater Heal if the damage ist not constant, or if you need to move a lot. Greater Heal is reserved for situations when you are able to stand still and concentrate on the healing task.