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There are a lot of people asking about how Ion damage works in FTL, and a few different theories floating around that don’t quite match up, so I decided to do some testing and figure out the mechanics behind it. Here’s a breakdown of everything I found out.

(All this info has been tested in-game and is 100% accurate).

1. Ion weapons don’t deal damage like normal weapons, instead they deal ion damage. Each point of Ion damage ionises (temporarily damages) one bar of system power for 5 seconds. So an Ion Blast will ionise one bar for 5 second, a heavy Ion will ionise 2 bars for 10 seconds, and an Ion Bomb will ionise a whopping 4 bars for 20 seconds! Ionised power goes back to the reactor, just like it does for physical damage.

2. When a weapon is ionised it is also locked down. During this time you can’t add or remove power from the system, although un-ionised power bars will still power the system as normal. Also, a locked down system can’t be manned by a crewmember, and any bonus for manning the system is lost. (After you use a cloak or teleporter, they will also enter lockdown for a short time.)

3. Ion damage stacks, so if an Ion weapon hits an ionised system it will ionise more power bars and add more lockdown time. However, if the lockdown counter reach zero, ALL the ion damage disappears and the system returns to full power.

4. if an ion weapon hits a shield it counts as a direct hit to the shield room itself, doing the full amount of ion damage the weapon does normally.

5. Ion damage and physical damage don’t stack, so any physical damage dealt to an ionised system will knock out ionised power bars. Ion damage will only ionise active power bars, so having extra inactive power bars won’t act as a buffer like it does for physical damage. Also, the maximum lockdown time for any one system caps out at 25 seconds.


For a more practical guide on how to use ion damage, check out this article.

Ions also damage Zoltan shields (including the Flagship's shield) more. I think 2x more.

Teleporters and cloaks ion themselves. If a teleporter is hit with an ion blast during its cooldown, that ion will stack with the teleporter's intrinsic self-ioning.

I thought ion damage seconds were capped at 5 seconds.

They cap at five "timers", each timer lasting 5 seconds, so if your enemies teleport an ion bomb in your teleporter, for example, shortly after you've teleported, it will stop at 5.
That's also the reason why 2 Ion weapons can basically bring down any number of shields through sheer spam - seriously, the only exception being the Ion Blast Mk II, but that's only because it fires twice as fast, sucessfully bypassing the timer. The Ion Bomb does that too, but it costs a missile.

Noobjuice wrote:Ionised power goes back to the reactor, just like it does for physical damage. (Double check this)

Yes, this is correct.


Understanding ion damage is understanding why the Ion Bomb is the best weapon in the game and Heavy Ion is one of the worst. (Heavy Ion's 13s cooldown means that it cannot chain with itself - so unless you're pairing it with another ion weapon, for most practical purposes it's an Ion Blast I that fires slower and costs an extra power to use.)

Twinge wrote:Heavy Ion's 13s cooldown means that it cannot chain with itself

That statement is misleading. A Heavy Ion can stack with itself if you get an Automated Re-loader and man the weapons (skill not needed?), or get two Automated Re-loaders. That gets the cooldown under 10s to allow it to stack itself. I think I've had two runs where I've done that.

edit: Yeah, my first time was with two Automated Re-loaders, and the second time was with one, which surprised me because I didn't realize I could do it with one.

RAD-82 wrote:

Twinge wrote:A Heavy Ion can stack with itself if you get an Automated Re-loader and man the weapons (skill not needed?), or get two Automated Re-loaders. That gets the cooldown under 10s to allow it to stack itself.

True, Reloaders are another way to get there. You can just barely chain it with one Reloader + Level 0 Crewman, but the margin is so thin that once the shields are actually down they'll go back up because of the extra travel time (the outside shield bubble compared to the Shield System). Level 1 Crewman works normally, though.

By chance I was able to test the Heavy Ion yesterday (in that game the RNG kept throwing Ion weaponry at me like crazy...) and indeed it stacks with itself when using an Auto Reloader. It's even quite satisfying to remove one bubble per shot as opposed to Blast MK2's to shots per bubble.