To listen to some keepers talk, you would think that humidity was some sort of mystical potion that was difficult to make but that works magic. While it may be tough to provide the high humidity we aim for if the air in your tortoise room is dry, the overall idea is simple. There are three basic rules to humidity-
Why is humidity important?
For red-footed tortoises and most other common pet species, 50-70% overall is probably enough, especially if there are hides or other areas with higher humidity available.
We can raise the humidity in our habitat by…
The method that works best for me in the rather cold and dry Great Plains region is the one described in ‘Basic Housing’- a waterproof heat rope in the substrate that heats the water to generate warmth and humidity. My habitat is about 60% covered, and still stays very humid with very little attention- daily watering and checking water levels, and a thermostatic controller for the heat ropes so they are at the temp I want them at.
Too much humidity, especially combined with heat, low air flow, and so forth, can lead to issues like mold and mildew, a smelly habitat, plastron rot, etc. A good airflow will help, as will things like live plants, a good substrate (like cypress), and regular monitoring.
If you can, consider an airflow that lets a relatively small amount of air out at the top- small holes drilled around the edges of the lid, but has more and/or larger air holes around the base. The warm humid air will leave slowly through the high holes, and new, fresh air will come in easily in the low holes.
What is humidity?
Absolute humidity (AH) is how much water vapor there is in a given amount of air. (AH) is determined by dividing the mass of the water vapor (Mw) in a given volume (V), or AH = Mw/V. This is not as helpful to us as ‘relative humidity’ is.
Relative humidity (RH) is determined by a rather complicated formula, but the idea is simply how much vapor is really in a space compared to what it could hold total. This changes as the air gets warmer, pressures change, etc.
A cubic meter of air at 30c/86f can generally hold 30 grams of water vapor (shortened to 30gr/C^3), making it 100% relative humidity. If the absolute humidity was half that- 15gr/C^3 and the temperature was the same, the relative humidity would be 50%.
As the temperature of our cubic meter of air cooled, it could not hold as much water vapor. The excess vapor becomes condensation, dew, or fog- but the relative humidity could still be nearly 100% because it is still holding as much vapor as it could at that temp. This relates to the ‘dew point’- as the temperatures drop, the relative humidity is rising. When it hits 100% and the temperatures keep dropping, the vapor it can no longer hold becomes dew.
Homemade humidity devices
These are mostly just brainstorms and ideas, not finished thoughts.
Small plastic, lidded box or tub with an access hole in the side. (My example uses part of the door to make a ramp, has non-skid tape on the ramp, and curtains of plastic strips.)
Add an inch or two of dampened sphagnum moss or similar product, and park the box in a warm zone to make a nice, humid chamber. A better alternative is to sew some absorbent material (like the same kind of moss) in a thin cloth bag and hang it on a side- less moisture on the hide floor.
A small heating element (water-proof hot rock?) can be used in or under it to keep the temps comfy.
This is a plan for providing warm, humidified air for a large semi-enclosed space, like a big tortoise table. It is only an idea, and this is not meant to be a blueprint!
The idea is that a ceramic element space heater (with thermostatic controls, an intake filter, and a fan speed control set to low) blows into metal ducting that leads into a large plastic tub.
Inside the tub is a powered humidifier (the thing shown is a fogger unit on a brick in a pool of water.) The inside is also divided by baffles to slow the warm air so it absorbs more humidity. A second duct takes the filtered, warm, humid air into the habitat.
Take a plastic bottle with a big mouth lid, install two tubes- a small one hooked up to an air pump on one end and an airstone on the other, and a larger tube to carry the humidified air to the habitat.
This is not a very powerful humidifier, but it is improved by adding a bigger pump, or a wick/sponge inside to help move water to vapor faster, or heating the water. It also helps to direct the output into a small, semi-enclosed space- such as inside a hiding log.
(Do you like how it is working even though the air pump is not plugged in? Gotta love that Acme brand!)
Start with an automatic pet waterer. Use 4 sponges to build a little ‘castle’ in the bowl area with a space in the middle.
Take a plastic tub that fits over the sponges nicely and cut a hole in each side and the top. Attach a small sealed fan on the top- blowing down. (Radio Shack sells small computer fans that will work. Get help if needed to wire it safely!)
Fill the waterer and set the tub down over the sponges. Trim sponges to allow a good fit.
The air will be pushed past the wet sponges and blow humidified air out the holes in the sides of the tub.
The large reservoir lets this run for a long time between services, and a drop or two of vinegar in the water will help prevent mildew.
Mount a piece of something like terrarium moss, indoor-outdoor carpet, or similar material to a wall of the habitat. At the base of the material, park a pan or tray to catch excess water. A ‘drip vine’ along the top of some ‘reptile moss’, for example, would work nicely.
Position a dripper so it drips on the carpet. Drippers can be bought or made. Any jar with a spigot on the side will work if you can open the spigot just enough to let it drip out. A plastic milk jug with a pin hole in the side will work as well. With any dripper- how tight the lid is helps control flow.
People are always creating new techniques to heat or humidify reptile habitats. The internet and reptile chat rooms are a good place to get started. Some other ideas I have seen on-line include:
Edited 8-15-2012 (C) Mark Adkins