The question is pretty self-explanatory. Did someone do the math to know till what level the healing pot out-heals ignite? Assume that there is no other damage applied an no other healing applied.
Notice, that when I say out-heal I mean that the champion will live even if he had 1 hp at the moment that hp pot and ignite started ticking.
Best Answer
Healing Potions heal for 150 health over 15 seconds, i.e. 10 health per second
Champion regeneration is about 5 health over 5 seconds depending on the champion, i.e. 1 health per second
Ignite does 50 + 20 per level over 5 seconds, i.e. 10+4 per level per second and reduces healing by 50%.
That means if you are at 1hp a health potion won't save you at any level with a reduced healing of about 5-6 health per second compared to 14 damage per second but you can survive it if you have more than ~40hp on level 1.
Healing Potions against ignite are more of a last straw, not a reliable way to counteract it.
http://leagueoflegends.wikia.com/wiki/Health_Potion
http://leagueoflegends.wikia.com/wiki/Ignite