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  1. #1
    Join Date
    Jan 2007
    Coloma MI

    Thumbs down Hot Tub Room ventilation

    I have built a room off of my walkout basement for my Spa. The room is 10x12 with a 12' vaulted ceiling with 2 18x30 double insulated skylights. The east wall is all aluminum framed double insulated glass, north wall is framed with 1 window, insulated steel door and R-13 insulation. South wall is similar with 1 window. The west wall is the outside basement wall. Ceiling is insulated with R-19 fiberglas, with fanfold foam covering it as a vapor barrier. There is good airflow between the underside of the roof and the insulation with soffit vents and full ridge vent. All walls are R-13 fiberglas, also with fanfold foam. The ceiling is finished with tongue & groove pine treated with thompsons water seal. The walls are all finished with Tongue & Groove Cedar planking.

    This room is not heated except for the incidental heat from the spa which keeps the temp at 50 when outside temperature is 18.

    I have installed a 110 cfm vent fan in the ceiling which is controlled by a humidistat which turns the vent on at 65%.

    I have been given differing opinions by non professionals on whether or not I should have make up air in this room for the vent fan or not. I have been told that due to the humidity I want to keep a negative pressure to help keep the moisture out of the walls. Other opinion is that I should install a passive barometic type vent to bring in outside air.

    The room is sealed from the rest of the house by insulated steel french doors and when using the spa the humidity will get to about 90% but within 15 minutes of replacing the cover the vent has it back down to about 55%.

    Do I need to provide make up air or should I keep a negative pressure??

    Any other suggestions are welcomed also.


  2. #2
    Join Date
    Apr 2004
    If you expect anything to be exhausted you need to supply some fresh air.

    I made the mistake of putting a spa in a room before... Besides, there's nothing better than sitting in a spa with snow falling on your head.

  3. #3
    Join Date
    Jan 2007
    Coloma MI


    Thank You for the response Doc,

    Is there some type of passive vent you could recommend?

    I still have one wall that has not been finished on the inside that I could place a vent in.

    Standard 2x4 construction.

    I had originally thought about building a sheet metal box with a vent inside and outside at the bottom with a divider inside splitting the box in half with a gap at the top for air flow. Hopefully this would help eliminate drafts but still let air flow freely.

    I'm sure there is a better solution and any suggestions are much appreciated.

    I too am going to miss having the spa outside but it's only adding $12 a month to the electric bill inside as opposed to $34 outside.

  4. #4
    Join Date
    Jun 2004
    4H: Hot, Humid Houston H.O.
    I would take the viewpoint, if you are exhausting air then it has to be coming in from somewhere, in equal quantity. It could be from random leaks in the building structure. Cracking a window open will be one way to provide makeup air. You might be able to easily design something a bit more elegant that would to the job.

    I live in hot-humid S.Texas, so this is an interesting problem for me and I enjoy trying to see the answer. But I don't share the climate you live in, and people in your region might have better experience.

    Best of luck -- Pstu

  5. #5
    Join Date
    Jun 2003
    Madison, WI/Cape Coral, FL
    Negative pressure is king for keeping moisture out of the walls for humidity control during extreme cold weather. During warm weather, open a window. Maintain <50%RH in the ajoining basement with a good dehumidifier. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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