Firestorm

Perhaps the most feared area effect skill in the Witch's arsenal, the mighty Firestorm skill is legendary for its power and cruelty. The incantation tears a rift in the heavens that showers a wide swath of ground in a rain of searing flames. These bolts pound down without mercy, burning everything they touch, then exploding violently to cause even more harm.

Description on the official Path of Exile website

Skill Functions and Interactions

Area of Effect: Increased AoE will increase both the area in which the fireballs randomly fall and also the radius of the individual fireball damage. Full spell damage is done at any point within the AoE of a fireball, however due to the fact that enemies take up an area and not simply a point, less spell damage is dealt to any given enemy as area increases. This is why, contrary to popular belief, increasing the AoE of Firestorm decreases the average number of hits to single target.

Duration: Increasing duration with either supports or passives will increase the total number of fireballs that fall before the spell ends.

Damage Effectiveness: Damage from secondary sources like 'added damage' supports or heralds applies at only 30% of their listed value.

Damage per Second: Due to the complexity of estimating actual DPS of the skill including all possible factors, ingame tooltip shows only average damage per hit of one fireball, with actual DPS of the skill being considerably higher. The closest currently available estimate can be obtained by using the damage calculator.

Gem level progression

Level			Mana Cost	Fire Damage	Exp.	Total Exp.
1	28	67	13	23 to 35	0	0
2	31	73	14	29 to 43	199345	199345
3	34	79	15	36 to 54	285815	485160
4	37	85	16	44 to 66	401344	886504
5	40	92	16	54 to 81	554379	1440883
6	42	96	17	62 to 93	477437	1918320
7	44	100	18	71 to 106	583786	2502106
8	46	104	18	81 to 121	710359	3212465
9	48	109	19	92 to 138	1355511	4567976
10	50	113	19	105 to 157	1138877	5706853
11	52	117	20	119 to 178	1368233	7075086
12	54	121	20	135 to 202	1638338	8713424
13	56	125	21	153 to 229	1956648	10670072
14	58	130	21	173 to 260	3655184	14325256
15	60	134	22	196 to 294	3017327	17342583
16	62	138	22	222 to 333	7759995	25102578
17	64	142	23	251 to 376	15138193	40240771
18	66	146	24	283 to 425	26083825	66324596
19	68	151	24	320 to 480	62620247	128944843
20	70	155	25	361 to 541	211708088	340652931
21	72	159	25	407 to 610	N/A	N/A
22	74	N/A	26	458 to 688	N/A	N/A
23	76	N/A	26	516 to 774	N/A	N/A
24	78	N/A	27	581 to 872	N/A	N/A
25	80	N/A	27	654 to 980	N/A	N/A
26	82	N/A	28	735 to 1102	N/A	N/A
27	84	N/A	28	826 to 1238	N/A	N/A
28	86	N/A	29	927 to 1391	N/A	N/A
29	88	N/A	30	1041 to 1562	N/A	N/A
30	90	N/A	30	1169 to 1753	N/A	N/A
31	91	N/A	30	1238 to 1857	N/A	N/A
32	92	N/A	31	1311 to 1966	N/A	N/A
33	93	N/A	31	1388 to 2082	N/A	N/A
34	94	N/A	31	1470 to 2205	N/A	N/A
35	95	N/A	31	1556 to 2335	N/A	N/A
36	96	N/A	32	1648 to 2472	N/A	N/A
37	97	N/A	32	1744 to 2617	N/A	N/A
38	98	N/A	32	1846 to 2770	N/A	N/A
39	99	N/A	33	1954 to 2932	N/A	N/A
40	100	N/A	33	2068 to 3103	N/A	N/A

Alternate skill effects

Name	Cost	Description
Siege Firestorm EffectSiege Firestorm EffectSkill Gem EffectYour Firestorm becomes a flaming siege assault	25	Replaces the standard projectile effects on a gem with burning cages of spiked metal. Preview

Related helmet enchantments

The following helmet enchantments affect Firestorm.

Note that helmet enchantments are no longer obtainable since version 3.23.0 and can only be obtained in permanent leagues as already enchanted items from before this patch.

Name		Labyrinth	Stats	Spawn Weighting
Enchantment Firestorm Damage 1	66	Merciless Labyrinth	25% increased Firestorm Damage	helmet 100
Enchantment Firestorm Damage 2	75	Eternal Labyrinth	40% increased Firestorm Damage	helmet 100
Enchantment Firestorm Duration 1	66	Merciless Labyrinth	20% increased Firestorm Duration	helmet 100
Enchantment Firestorm Duration 2	75	Eternal Labyrinth	30% increased Firestorm Duration	helmet 100
Enchantment Firestorm Explosion Area Of Effect 1	66	Merciless Labyrinth	16% increased Firestorm explosion Area of Effect	helmet 100
Enchantment Firestorm Explosion Area Of Effect 2	75	Eternal Labyrinth	24% increased Firestorm explosion Area of Effect	helmet 100

Version history

Version	Changes
2.1.0	Damage increased by around 20% higher at level 20.
2.0.0	Firestorm: Had a very slight damage buff. Area of effect of explosions increased by 11% (9 to 10). It now grants 1% area damage per 1% quality instead of reduced delay between fireballs. The Duration of Firestorm has been increased from 1.3 seconds to 2 seconds at all levels. Base Cast Speed has been increased from a cast time of 1 second to 900ms. Critical Strike Chance has been increased from 5% to 6%.
1.0.4	Firestorm: The radius of the area that fireballs land in has been increased by 39%. The delay between strikes has been reduced from 0.15 seconds to 0.10 seconds. Damage has been increased by 35%. The quality bonus has been reduced by 33.33% to match the reduced projectile delay.
1.0.0	Reduced mana cost.
0.11.2	The damage done by the Firestorm spell when used by all versions of Ambrosia and Merciless Fire Fury has been increased. Merciless Gravicius's Firestorm has been very slightly increased in damage.
0.11.1	Spells with Damage Effectiveness no longer have their own damage affected by Damage Effectiveness. Damage values on these skills have been updated to reflect this.
0.9.12qq	Fixed a bug where monsters in high level areas would not do the correct Firestorm damage.
0.9.11i	Fixed the randomness when it was used with Traps.
0.9.11f	Increased the damage and made its cluster tighter.
0.9.9	Fixed a bug where the damage from Firestorm would not display on the client at the right time.
0.9.6	Changed Firestorm to be affected less by additional damage from support gems. Fixed a bug where Firestorm could hit monsters through walls.
0.9.5	Modified Firestorm's behaviour so that the explosions have a larger radius and are more likely to fall near the centre of the affected area. Doubled the number of fireballs that fall and rebalanced damage around these changes.
0.9.3c	Raised the overall damage and its high level damage scaling.
0.9.3	Firestorm has been added to the game.