It's a good question, and I only just "discovered" Holy Nova myself. I can still remember when it was a talent in the holy tree (wasn't it even the end talent back in vanilla?), and the only aoe damage priests had at that time. In Wrath I rarely used it, not because it wasn't any good (well it wasn't very good actually) but because I had tons of other tools to help me out already. I never had to look at Holy Nova and think "where I can fit this into my healing rotation?". But as we've all noticed, things have changed rather dramatically in Cataclysm, and the reason I've started to use Holy Nova is because it actually fills a gap in my healing arsenal. The "on the run instant spammable heal". It might not be needed often (especially not in heroics) but we should be glad we have it, because no other healer does. So let's take a closer look at Holy Nova - how useful is it anyway?
- For disc this is the only tool we have to heal multiple targets on the run. There is nothing else. In this case Holy Nova becomes a rather important spell in our arsenal.
- It is instant, aoe and has no cooldown. Every healer loves these heals (eventhough they might not use them often, having it is still better than not having it), and not very many have them. Actually HN is the only spammable instant heal in the game, and we should cherish it. The only competitors are hots and shields, which are single target.
- Causes no threat.
- Works like any other heal, meaning it can proc Echo of Light and Divine Aegis (but not Inspiration).
- Isn't targettable but emanates from you. This means you will always be one of the targets healed.
- Has very limited range (10 yards).
- The healing done by the spell is actually divided among targets (as the tooltip explains). What that means is that it has (or rather should have) the same hpm no matter what amount of targets you hit. This isn't entirely true however since it doesn't seem to divide the heals in a straight line (ie 1 target for 5000, 2 target for 2500 each and so on). Rather, it seems to heal one target for ~4000 (my stats), 3 targets for a total of ~6000. It seems to have a minimum heal of ~2000 per target, but this is guesswork from me based on some testing.
Holy Nova Vs CoH & PoH
Just measured by the tooltip (not taking into account any gear at all) the mana efficiency of Holy Nova is about one third of CoH and one 6th of PoH, this is not taking into account the extra spellpower gain PoH gets from having a cast time either. The problem with Holy Nova is that the healing is iffy, to say the least. With some extensive testing I've had it heal between 1500 and 2500 per person, with the same amount of targets. One can safely say that HN is the least mana efficient aoe healing spell we've got, and also it has some other drawbacks as mentioned. However, having a heal to use on the move is very valuable, and HN should be considered part of your healing arsenal when raiding. At any time when your raid has to be on the move whilst also taking damage this is a helpful spell, and most boss fights have these moments. It's no use to save mana for jam tomorrow, there has to be a balance to it.
Examples of usage;
Valiona & Theralion - When moving out from Blackout dispel in phase 1, when moving out from Void Zones in phase 2.
Magmaw - When moving out of lava spew.
Atramedes- When moving away from the Sonar Pulses.
Chimaeron - When stacking up for Feud (until you've positioned yourself), to heal up a group 10k hp as disc.
Nefarian - When moving up on the pillars.
When to not use HN
As long as you keep an eye out on your mana bar, HN is a good spell to keep handy. It's easy to overuse however because it's instant and has no cooldown, so here are some areas where you should skip it. They might seem obvious, but should still be in the back of your head at all times;
- Whenever you've got CoH off cooldown.
- Whenever you can stand still long enough to cast a PoH instead.
- Whenever less than 4 targets (including yourself) will benefit from the cast.
To think about
Holy Nova is alot like Flash Heal. It's a costly spell and the areas of usage rather limited. But they do exist. Don't make the error of not using HN at all just because it has some flaws, and don't make the error to overuse it just because it is simple. As with every other heal it has its place in our healing arsenal and will do wonders when used correctly. There is a glyph of Holy Nova which decreases the gcd of it by 0.5 sec. This will increase Holy Novas hps, but not its hpm. There are some optional major glyph slots to be had as priest, so this could be worth having around. Glyphing HN doesn't mean you should use it more often, but that you might be able to use it more effectively when you need it.