You control the humidity with the level of water inside... More water higher humidity... When I used them I always kept it full... and when it was low... I got the same humidity readings? Youd be surprised as it just barely pumps out fresh air/humidity. If your using a heat light you def want the set up on the opposite side of the tank. If you dont youll just be adding humidity to be sucked up by the light, not helping your humidity proble.They get the job done but dont work nearly as well as a room humidifier. If you only have a couple snakes and have humidity problems I def reccommend buying this. Also think about investing in plexi glass to cover the top of your tank to keep the humidity in once youve created it.