I have developed a non-direct electric, non-heat, non-stagnant air method of increasing humidity for moisture loving tortoises. (G. carbonaria,  I. elongata, Terrapene species,  etc.) and for micro climate duplication in indoor habitats.

For those of you with access to lab glassware run the output from an aquarium air pump  through a gas sparge bottle.  The output is then run through aquarium tubing to the habitat in question.  Using this method I have been able to raise the ambient humidity from 50% to 75 % with no heat added and no direct electrical  contact possible with the animals. Also with no open water in the container in question.  In addition the habitat - in this case 30 inches by 12 inches (75 cm X 30 cm) did not have a full cover on it - so the air was not stagnant.

In the interest of husbandry I  developed a way to do this without access to lab glassware.  The lid from a one quart jar is holed twice. Through these two holes is placed aquarium tubing one piece barely passing through the cap the other longer. Once the tubing is through the cap  the holes are sealed around the tubing with silicone cement. To the long piece an air stone is attached (fritted disk)  this is placed in the jar that is filled with water.  The short end is attached to a long hose that runs to the habitat.  The pump is turned on and the air passes through the air stone and picks up moisture which is carried as  an ultra high  humidity air stream to the habitat there by raising the humidity and doing air exchange at the same time..

This works well, is cheap and no heat is produced just remember to keep the jar filled as it evaporates rapidly.

If you have an incandescent light in the tank the convection currents set up force one to cover at least part of the top. Making it necessary to do some experimentation to get your desired humidity level. This combined with the speed of the air flow and the size of the bubbles also has a bearing on the humidity increase.  I use one of these for my habitat with my baby elongateds in it,  30 inches  (76 cm) long by 24 inches (30 cm) wide.  In the day the humidity drops to about 50% as the tank is always uncovered and the light sets up the convection currents,  at night the humidity increases to over 80 %  Covering  2/3 of the top of the tank allows me to attain a humidity of 65% in the day with the light on and 85% at night .  Covering the tank totally I would assume would increase the humidity to higher levels.  My thinking is that the covering of the tank would possibly not adversely effect the inhabitants because of the air exchange that is a by-product of the apparatus.

I have found that this works best if you place the outlet hose actually inside the hide box through a hole drilled in the top. The added enclosure makes for a very high humidity in this very natural micro climate.  For my I. elongata and G. carbonaria I am using this and the humidity in the hide box stays above 85% throughout the day.

I feel that this apparatus has wide spread application especially with hatchlings of all tortoise species. Typically terrestrial chelonians spend much of their time in "resting forms", "pads", "scrapes" or burrows that experience a higher humidity than ambient.  The use of this apparatus helps to duplicate such a localized humidity.