Well this all highly experimental, and obviously if someone finds a cave (not an open shaft) by detecting a warm draught coming out of a tiny hole that can be dug, well then this would be the whole point of the exercise. That's why in the video we sparked up the joss stick to see which way the draft was going. We thought we would see nothing as the draft was going in, but then the cave entrance showed up 'red hot' with the cold air going IN. There is no reason why in a cold day when the atmospheric pressure is on the rise, and hence would suck out the drafts out of caves (to equalize pressure inside), that the camera should not see the whisps of warm air, even through a small hole. This is pure theory of course. Lets see if someone can put this to practice.
