One word of warning - don't try to pour water on the wax burner to put it out! Snuf it out instead.

One of the boys in my son's troop brought one of these to summer camp a few weeks back. It stayed lit for a looooong time. He used it to boil some water. He put the small can inside a large can (with holes punched top & bottom) and the pot sat on the top of the larger can.

When finished another boy tried to put it out by pouring water on it (before I could stop him) and the wax spattered everywhere. Lesson learned. By the way, after the drenching it dried overnight and they were able to relight it the next day for even more burn time.