Holy Priest Healing With Flash Concentration

Mechanical Priest

Flash Concentration is a shiny new legendary power available to us in Shadowlands. Obtained from Grand Proctor Beryllia in Sanguine Depths, this legendary power can be crafted onto your Neck or Wrist. Equipping it causes casts of Flash Heal to grant you a short 15-second buff stacking up to 5 times that both reduces the cast time of Heal, and increases its healing. Flash Concentration changes how you prioritise casting your filler spells, placing an emphasis on Heal. When played well it can provide an immense amount of efficiency and HPS. When played poorly it can lead to lower HPS and mana starvation.

Flash Concentration really turns Heal into a filler powerhouse. Heal becomes stronger than all the other filler options in terms of both HPS (throughput) and HPM (efficiency).

Before we get into the details though, the only part most of you will read…

The TL;DR

You don’t have time to read through that crazy Holy Priest dude’s thesis on how a basic legendary power functions. That’s fine, the main takeaways are:

If any of those don’t make sense or you want to read more, then dust off your reading glasses. It’s thesis time.

Screenshot of WarcraftLogs showing 97-100 parses.
Flash Concentration is ok.

How Flash Concentration Works

To use Flash Concentration effectively, the main thing you need to understand is that getting to 5-stacks is good. Keeping it at 5-stacks is great, and casting Heal is amazing.

Each time you cast Flash Heal, you gain a stack of the Flash Concentration buff. This buff reduces the cast time of Heal and increases the healing it does for each stack you have. The buff will stack up to 5 times, so each time you cast Flash Heal it will add another stack until you reach 5. Casting Flash Heal will also refresh the duration of the buff to the full 15-seconds.

Now you have some stacks of Flash Concentration active, each Heal you cast benefits from it. Casting Heal will not remove a stack, or remove the buff at all. You can cast Heal as many times as you like and each one will benefit from all of the stacks you have active at the time of casting. Before you can use it though, you need to craft it!

Flash Concentration legendary tooltip. Each time you cast Flash Heal, Heal has its casting time reduced by 0.2 sec and healing increased by 3%, stacking up to 5 times.
Flash Concentration. Simple, yet effective.

Crafting Flash Concentration

To go with the theme of Shadowlands giving you choices you don’t really want to be forced into making, you first need to decide which slot it goes on. There’s a number of considerations that can be taken into account regarding which slot works best for you:

  • What gives more stats? This question isn’t so much which of the two slots gives more stats, but which of the two slots in a higher item level gives more stats than their lower item level counterparts.
  • What is your focus? If it’s killing the final boss in Mythic Raid then you ideally have the best gear possible for the hardest fight in the raid.
  • Do you value Best In Slot? BiS once the raid is over is pointless to most people.
  • Do you care about the next tier? Basing your slot decision purely on this tier is going to leave you in a weird situation next tier where you may not have the ideal slot but still feel you should have it.
  • What is your legendary base availability? Depending on your realm, guild and content level you may have trouble accessing or affording the higher tier bases. Your Tier 4 cloth base being 500k on your realm while the Tier 4 jewellery base is only 20k is certainly a deciding factor for many people.

Overall, the short version is the impact on your performance your legendary slot has is very very minor. It will depend entirely on your situation and it will fluctuate between gear upgrades, encounters and tiers.

My suggestion? The difference is small enough it won’t matter. Jewellery is great, they’re safe slots that let you customise a large chunk of secondary stats, and they also allow you to trade items in those slots to more classes than just other clothies.

Now you’ve chosen a base by throwing your favourite dart at the gear-slot dartboard, you need to decide on your two secondary stats. Ideally you should choose stats that make the most sense for the content you’re participating in.

  • Primarily raiding? Choose raid favoured secondaries (Mastery/Crit/Vers).
  • Primarily doing Mythic+? You guessed it, choose mythic+ favoured secondaries (Crit/Haste/Vers).
  • Doing a bit of both? Unsurprisingly, secondaries that are good for both raid & Mythic+ (Crit/Vers).
Flash Concentration tooltip on an in-game neck at 210 item level.
Flash Concentration at 210 ilvl in-game.

The Flash Concentration Build

There really isn’t much to it that differs from our regular toolkit though, just two of talent changes that enhance Heal some more. If you want to read a more in-depth explanation of how some of our talents work, check out the Holy Priest Compendum. Below are the talents that should usually be taken with Flash Concentration, regardless of your content type (view talent calculator). The level 45 and 50 talents are more content-specific.

Screenshot of the talent pane showing Trail of Light, Angelic Feather, Guardian Angel and Surge of Light chosen.
Flash Concentration Talents

Trail of Light

Trail of Light is the first talent change you should make.

Trail of Light tooltip. When you cast Heal or Flash Heal, 35% of the healing is replicated to the previous target you healed with Heal or Flash Heal.

This talent can be a bit tricky to explain in a coherent way, so I won’t go too in-depth on how it works. Basically, when you Heal or Flash Heal a target, the last person you cast Heal or Flash Heal on before them gets a Trail of Light for 35% of the amount. Examples:

  • You Heal your tank ɨʟʟɨɖǟռ for 10,000.
  • You Heal your hunter friend légőláś, who is standing in fire, for 10,000
  • You Heal your hunter friend légőláś, who is still standing in fire, for 10,000
  • You Heal the mage, who just cauterized because they didn’t want to move away from their rune of power, for 10,000
    • légőláś gets a trail of light heal for 3,500 (which is good as he’s still in the fire??)

As you can see, the ideal play is to keep moving your Heal and Flash Heal targets around to the people most injured or in danger of death. Trail of Light will then provide additional healing to the previous person you healed, helping top them up. Avoid topping someone up with a Heal or Flash Heal cast where possible, this way your next Trail of Light on them won’t fully overheal.

Surge of Light

Surge of Light (SoL) hasn’t really been used in raid since Emerald Nightmare in Legion. Anyone who has played Holy Priest in Mythic+ though should be familiar with the free, instant-cast heal procs it grants you when you cast healing spells.

Surge of Light tooltip. Your healing spells and Smite have a 8% chance to make your next Flash Heal instant and cost no mana. Stacks to 2.

Surge is vital to helping sustain your Flash Concentration stacks without taxing your mana. Surge of Light lasts for 20-seconds so you can get away with essentially ignoring you have this talent entirely if you want to keep things simple. Just cast Flash Heal whenever you need to refresh your Flash Concentration buff.

For those wanting to min/max it a little more or understand how it works a bit deeper; Surge of Light has a percentage chance to proc when you cast specific spells. Yes, it’s that old it still has a percentage chance and isn’t ppm (procs per minute) or rppm (real ppm). Due to being a percentage chance to proc instead of the more common RPPM system, it only has a chance to proc from a very specific whitelist of spells:

As you can see, it’s not all spells we use but it’s most of them. The most notable here is Smite. Surge of Light effectively gives Smite priority over all of your other damage spells due to Smite‘s ability to proc it. This doesn’t mean you never cast Shadow Word: Pain or Holy Fire, especially in Mythic+. But any fight you’re taxed for mana you should consider focusing on Smite as your downtime/damage filler.

Surge of Light can have up to 2 stacks. This means you not only should have a way to easily track how long Surge has left, but also how many stacks you have. Getting another stack while you already have 2 effectively causes you to lose a potential free Flash Heal. Casting Flash Heal on 2 stacks is ideal to maximise your overall HPM throughout a fight. You can even push this a bit further and use your Surge of Light stacks while repositioning to allow you to heal on the move.

Resonant Words

I know I said there were only two talent changes to this “build” but for the sake of completeness, it’s worth mentioning Resonant Words. At the time of writing this post, Resonant Words is the best potency conduit available to Holy Priest regardless of your legendary choice. So you’re running it anyway, right? Right.

Resonant Words tooltip. 
Casting a Holy Word spell increases the healing of your next Heal or Flash Heal by 38.0%.

Resonant Words is worth mentioning again because we are already juicing up Heal with Flash Concentration and Trail of Light, this makes Resonant Words even stronger. There isn’t much to this conduit, most of its benefit is largely passive. There are however some small HPS gains to be had by trying to avoid casting both Serenity and Sanctify in a row, and instead trying to cast a Heal between them.

This also comes into play in Mythic+ (and on really rare occasions in raid encounters) where you are regularly using Holy Word: Chastise to control an enemy. You can then use the Resonant Words buff it generates to gain an additional buffed Heal cast.

Healing with Flash Concentration

This is the part most of you will be interested in.

A New Pre-Pull Ritual

Build up 5 stacks of Flash Concentration pre-pull, then drink back to full mana. You can do this well before the pull and just cast Flash Heal every 13-seconds to keep the stacks rolling. Do this alongside your normal pre-pull ritual of getting Prayer of Mending stacked on tanks.

Screenshot showing the in-game tooltip of 5 stacks of Flash Concentration.

Build It Up, Don’t Let It Drop

You want to go out of your way to ensure you don’t drop your 5 stacks of Flash Concentration. You do this by casting Flash Heal before the buff expires. Losing this buff multiple times a fight and each time having to cast 5 more Flash Heals to get it back up each time will really hurt your mana efficiency and HPS.

Surge of Light: Some important notes for correct usage of Surge of Light to keep up your 5 stacks of Flash Concentration:

  1. Surge of Light has a 20-second duration, meaning whenever it procs you can use that proc for your next refresh without needing to panic that it will expire and you need to cast it early.
  2. If you get a second Surge of Light proc granting you 2 stacks, you can immediately Flash Heal to refresh Flash Concentration and still have your remaining Surge stack ready in 15-seconds time for your next refresh. This is thanks to the 20-second duration on Surge. There is no point sitting on 2 stacks of Surge as any successive procs will not grant any additional stacks.
  3. Some good luck with Surge of Light procs and you can chain this for a while, getting free Flash Heals and buff refreshes all while being on the move.
  4. Surge of Light procs heal immediately. This means you can refresh as late as 0.1 seconds left and still not lose your Flash Concentration buff. That said, I wouldn’t leave it that late if possible – anywhere around 1-second to go is the latest I would try to refresh it with a Surge proc to avoid the risk of dropping your stacks.

Change Your Filler Priority

Prioritise Heal and Smite. For the last 2 expansions, we have had a variety of playstyles. Due to how Holy Priest works with Holy Words, our core playstyle revolves around regularly casting these highly efficient, high HPS holy words, then filling the gaps between them with “fillers” which work toward getting them back off cooldown as soon as possible.

Holy Priest fillers we usually cast without Flash Concentration are shown below.

  • Flash Heal – Fast but mana inefficient single target heal for saving lives.
  • Heal – Slower but more mana efficient single-target heal for topping people up.
  • Prayer of Healing – Slow and reasonably mana efficient high HPS AoE heal.
  • Smite – Doesn’t actually do any healing but it makes you feel like you’re helping without spending much mana.
  • Shadow Word: Pain – Again no healing benefit but you can spend very little mana for some added DPS.

Holy Priest fillers with Flash Concentration buffing us at the full 5-stacks are simplified:

  • Flash Heal – A spell to refresh your Flash Concentration buff before it expires every 15-seconds
  • Heal – Fast and mana efficient single-target heal for saving lives.
  • Heal – Fast and mana efficient single-target heal for topping people up.
  • Heal – Fast and high HPS heal for healing your group.
  • Smite – Still doesn’t do any healing but you get to contribute to damage and poke fun at your cohealers who don’t have Wrath or Lightning Bolt on their bars still.

One thing that should immediately stand out to you, the fillers you should be casting are simplified. Flash Concentration really turns Heal into a filler powerhouse. Heal becomes stronger than all the other options in terms of terms of both HPS (throughput) and HPM (efficiency). Smite also supersedes other DPS options in terms of pure healing output due to its synergy with Surge of Light.

Avoid Munching Resonant Words

Resonant Words procs after casting any of your holy words. While this will primarily be Holy Word: Sanctify and Holy Word: Serenity in raid, it will also proc from Holy Word: Chastise and Holy Word: Salvation. It is worth getting a Heal cast off between your holy word casts where possible. If you have to move and people need the healing, go ahead and use your instant casts to help save a life, but where possible try to get at least one Heal cast off before casting another holy word.

Don’t Forget!

As always, one of the most common mistakes we see a Holy Priest make when they’re performing poorly is neglecting regular usage of our short-cooldown spells. The following should be cast as often as they will do healing, which should be nearly on cooldown! This is extremely important for both our HPS as well as our mana efficiency.

Check out either of the guides below for more specifics on how to optimise your rotation both with or without Flash Concentration. As a nice bonus, the Icy Veins one now has a tickbox you can select for Flash Concentration which will customise the casting priority for you.

Screenshot of the Icy Veins rotation page with Flash Concentration legendary power ticked.
Customise the Icy Veins rotation priority

How Does Heal Compare To PoH?

Warning: Math. It’s Napkin Math though which is Math’s less intimidating cousin. I’ll walk you through it.

The main filler comparison for a raiding environment that is relevant is Prayer of Healing. Prayer of Healing is the main filler spell for raid healing and usually does the most healing out of all your filler casts, when not using Flash Concentration. So how does this super-buffed Heal compare to Prayer of Healing and when, if at all, should you be casting Prayer of Healing when wearing Flash Concentration?

Below is some napkin math comparing the two in a few different scenarios.

Note: This isn’t a complete comparison as there are some more variables at play in a typical encounter but this is adequate for the purposes of answering our question above.

Note: SP% is Spellpower, which is the underlying value all spells multiply against your intellect to get their healing amount. For example, 100% Spellpower coefficient with 500 Intellect would heal for 500.

Picture of a table showing the comparison between Heal and Prayer of Healing with different modifiers such as Flash Concentration, Trail of Light, Prayer Circle and Resonant Words.
Heal vs Prayer of Healing in various scenarios

We can see that without Resonant Words, casting Heal overtakes Prayer of Healing with healing done per second (Total SP% /sec) at 4 stacks of Flash Concentration (279% vs 272%). With 5 stacks of Flash Concentration, Heal is much further ahead (320% vs 272%). So using this simple comparison, at 5 stacks of Flash Concentration, it is always more raw HPS to be casting Heal rather than casting Prayer of Healing. Obviously then factoring in Resonant Words procs, Heal pushes even further ahead.

Now looking at mana usage, Heal is immediately more efficient than Prayer of Healing even at 0 stacks of Flash Concentration (0.13% vs 0.10%). This shouldn’t really come as a surprise to anyone, as Heal has always been touted as the mana efficient filler.

Our final comparison from this table is the HPS (Prayer Circle SP% /sec) during a proc of the Prayer Circle talent. This favours Prayer of Healing over Heal (320% vs 354%). This isn’t a big surprise either, as a 25% reduction in cast time was bound to really help Prayer of Healing’s case. The counter-point to Prayer Circle is that this increased HPS is only during the 8-second window after casting Circle of Healing. There is then a window after that where this talent is not active and the HPS drops back to 272%. Meanwhile, Heal with Flash Concentration keeps a steady and reliable HPS amount constantly while being much more mana efficient.

As a final note on this table; It also demonstrates really well just how important it is to keep your Flash Concentration stacks up. Dropping them hurts not only the HPS but also the HPM of your Heal casts.

The Very Specifics

For anyone looking to make weak auras or wanting spell IDs for adding to other tracking addons:

Side note on Trail of Light; It’s a common request to display the Trail of Light target on your frames. To do this you would have to track the last two people healed by Heal or Flash Heal. The reason for this is if you target the most recent person, the previous one will be the one getting Trail of Light. If you know of someone who has put the time into implementing this as a weakaura or addon please let me know and add it to the resources!

Below are some Flash Concentration tracker weak auras to get you started.

That’s All Folks

So there you have it, in 10,000 words or less, why you should change 2 talents and press Heal a lot when you have Flash Concentration equipped.

Best of luck with your new legendary and try not to get too frustrated at your stacks dropping off. 😅

More questions? Have logs of you carrying the healing, or failing miserably with Flash Concentration that you want to share? Drop by #holy on Discord.


You can follow me on twitter at @MechPriest and support me on Patreon.

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