Is there a minimum size for Chanuka flames?

Question

Do the flames atop the chanukiya need to be a certain size to be valid? At the extreme, are tiny (but sustained) balls of blue flame sufficient?

Answer 1

A fire is a fire is a fire - See OH 673(1)

ואע"פ שאין השמנים נמשכים אחר הפתילה ואין האור נתלה יפה באותם הפתילות

Even though the wicks don't absorb the oil well and the light [fire] doesn't attach well to those wicks (--translation mine)

(i.e. even if your lights are poor, your still yotzeh the mitzvah).

That being said, the מצוה מן המבחר is to use materials that will give off a light that is "pure and clean" (Rama, ibid.). The Mishna Berura also something along the lines of what @doubleaa said: The goal here is Persumei Nisa. Hence, if people can't see them, you may have an issue at hand.