` Yes, the fan can remove too much humidity on certain cages. It can also over-cool certain cages. If you slap a fan on the wrong cage, you'll have some distressed critters.
` After years of fooling with herp caging, I have a set up that works so well, I haven't made a reptile sick in many years.
` ALL of my cages are sealed on the top, and sides, and sealed tight. Vents are only in the lower third of the cage. I use some of the aquarium type cages with sliding screen tops, for smaller critters. Those, I turn on their side, and seal all but the bottom 2 inches of the ( now ) side screen door with plastic wrap ( food grade ), and silicone sealant.
` I have found that the cheap humidity gauges are worse than useless. Radio Shack has one for around 30 bucks that reads local temp, remote temp, and local humidity. It is quite accurate I have several which have remained accurate for several years. These are invaluable.
` Before you put a fan on a cage, you've got to know the heat, and convection characteristics of that particular cage. Each one is different, as I do not keep my herps in a specially heated room, except when they're loose. That's where the timer comes in. I use the mechanical, rotary type with 24 on/off settings. Once I have a stabile cage set-up, I then experiment with the timer until I find the right timing. I start out with too little circulation, then work up in VERY small increments. Those little fans don't move enough air to need a rheostat, for my large cages.
` I heat the entire floor of my cages, so air temperature is not too important. But with sealed cages, air temperature is very constant.
` I think you ought to know exactly how much your humidity varies, over 24 hours, and how much you have at minimum, and maximum, before you install fans. I actually started using the fans because I needed to remove some of the humidity.

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