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I also have an indoor hot tub (HS Grande) and moisture was a big concern for us also. We have 5 sliding patio doors and 4 skylights above the tub that open. The floor is tile and we lay a towle down so the water that drips from the cover never even gets the floor wet. Also incorporated into this room is a wood stove and that does a wonderful job of wicking away moisture on the nights its just to cold up here in the Chicago burbs to keep the windows open. We are able to close this room off from the rest of the house and HVAC system so no additional moisture enters into the main part of the home. After several years I am happy to report never having any problems at all and we love have the tub indoors. Click on my name for a larger photo of the tub room.