Does humid air rise? Will the cigars at the top of my humidor be more moist than the ones on the bottom? There seems to be a lot of confusion about these simple questions. But by placing multiple hygrometers inside a large humidor, I’ve observed that humid air DOES rise. This observation is confirmed by a more scientific approach in this online article:
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html#c5
This understanding explains a lot. If water vapor was heavier than air, evaporation could not occure. But this unscientific explanation is very general and doesn’t take into account things like temperature, elevation, and other factors that I am not even aware of. But for a cigar collector, this rather simple generalization is good enough. For consistant cigar humidification, we need to circulate the air in our storage units and rotate the cigars in our humidors.
One simple way to S’plane it is to take a look up @ the sky on a day that has clouds, They are a collection of those same water vapors.
Finally someone raised the attention to this topic. As RobustoJoe described humidity DOES rise and all the humidifiers attached to the lid or placed above the cigars …well they are not getting as much humidity as they deserve.
Good to know that someone in Germany was aware of this problem and came up with the CigarSpa. It is placed on the bottom of your humidor where it belongs. The CigarSpa is a fully automatic humidifier and temperature controlling device. http://www.cigarspa.de/en/cigarspa.html It is not small and your humidor capacity might suffer a bit, but the remaining cigars will put a smile in your face.
I have found that the issue of water in air is very misunderstood. Moist air is neither heavier or lighter than air. Whether it rises or not depends on the energy it has. The observation that moist air rises and therefore there are clouds ignores the fact that there is also fog. When the sun shines on fog, dew, or any other water it will impart energy, (heat) and that water vapor start moving and rise. When it touches something cold it will lose its energy and stay on the surface, this is the condensation you’ll on the side of your cold drink. Evaporation also happens when wind blows across the surface of water and carries it up. This is how some humidifiers work.
Relative Humidity is a different thing and is a measure of how much water the air can hold which is a function of temperature and pressure.