Hi John, we have the identical problem here. I keep the redfoot tortoise too in the same room with my green iguana so I was going crazy trying to get the humidity up. I had some success with the hot mist type of humidifier but refilling it and cleaning it every single day was a huge drag. I finally went with the pro-mist last February. It has been wonderful. My biggest problem has been that the nozzles it comes with put out TOO MUCH mist and it pools up a bit and it is a breeding ground for bacteria. They sell a super low flow nozzle that takes care of this. The guy is at the white plains show every time and is a really nice guy and can help you out and advise you on what you might need in terms of nozzles and tubing.
I have one nozzle directed onto the redfoot habitat and that works great. It is on a timer (that it came with) that comes on for one minute once an hour. In fact the whole shebang comes on once an hour for one minute. 2 nozzles aim at where the green iguana sits most of the time.
In a room the size you are trying to humidify I would not be surprised if you had to leave the humidifier on as well tho.
Carole

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