Indoor or Outdoor

• This is the largest placement decision a person must make when purchasing a hot tub. When a hot tub is outdoors, the humidity naturally vents into the air around your home. Indoors, however, humidity becomes trapped. There are some obvious comfort and convenience advantages of an indoor hot tub to weigh against the humidity issue.
  
  

Ventilation

• The constant delivery of warm, humid air into a room will cause problems in many building materials as well as contribute to the formation of mold and mildew. Proper ventilation is critical to prevent this. An air exchange system must be installed for an indoor hot tub so that fresh air can be brought into the room as the warm, humid air is carried out.
  
  

Vapor Barriers

• A vapor barrier should be installed in a room with a hot tub in it, especially if the room is next to an exterior wall. If moisture builds up in an exterior wall, there is a high risk of freezing inside the wall which could damage the structure of your home. Plastic vapor barriers also must be installed to protect the wood, drywall and other components of your home's structure that could rot and mold if they become wet.
  
  

Dehumidifier

• If the ventilation system isn't doing a good enough job removing the humidity from your hot tub room, consider adding a separate dehumidifier. Dehumidifiers pull the moisture from the air. These units should be emptied occasionally, but if they are in the same room with a hot tub, existing drainage in the room can be used.