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Moisture management with a Hot Tub in the basement

artisanfarms | Posted in General Questions on

I’m planning to put a small hot tub in the basement of the house I am rehabbing and am looking for ideas on the best way to manage the vapor coming off the tub while it is opened and in use.  It will probably see 3-5 hrs a week of use.  I’m dealing with myelopathy and spasticity so the tub isn’t for purely recreational use, instead it is part of my exercise/therapy program.   The tub is a small inflatable tub with ~200 gallons of water and less than 25sqft of surface area but with the turbulence induced by the bubbler creates a fair amount of vapor.  

Where I am now, I keep it in the garage during the winter and just open the door when I am done for 15 min – 1/2 hr and that seems to do a good job.  

For the planned new location,  in the basement adjacent to the exercise area, I’d like to set something up that will ensure sufficient venting of the moist air, with minimal loss of heat.  

Any suggestions are welcome

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  1. Expert Member
    NICK KEENAN | | #1

    Have you looked into heat recovery ventilators?

  2. charlie_sullivan | | #2

    As DCContrarian says, a heat recovery ventilator would be the most energy efficient option. But depending on how often you use it, you might just opt for an exhaust fan like those used in bathrooms. You'd want to run it during and after use, and monitor the humidity to make sure it gets back down. You could use a timer after you get a feel for the amount of time it needs to run, or even use a humidistat to do that automatically.

    If you enclose the tub in a smaller volume room, or maybe something like a big shower stall with plexiglass walls and ceiling, the total amount of moisture you evaporate from it will be less than if you have it in a big wide open room--the humidity in the enclosure will get up to near 100% and the water will stop evaporating. Then you cover the tub and flush the air out of that enclosure with the exhuast fan, and never get much humidity into the larger room.

  3. Expert Member
    NICK KEENAN | | #3

    I agree that you want a small enclosed room, constructed out of stuff that the humidity won't bother. You still want to vent it when you're not using it to keep mold from growing. If you had a 10x10 room with 8' ceiling that's 800 cubic feet, a 100 CFM fan would replace all the air in 8 minutes. So use the hot tub with the door closed, then cover the hot tub, open the door, and turn on the fan.

    The question is where to vent the air. Outdoors is an obvious choice. Outdoors through a heat recovery ventilator might make sense. Or, in the winter, the heat and humidity might be welcome inside your house and you might want to vent it upstairs.

  4. Andrew_C | | #4

    We've had small hot tubs indoors in several houses, in the basement when possible. We only use it during heating season (Zone 5, about six month/year), so the air is generally drier. Keeping the insulated top on the tub when not in use, we've never had a problem. When located in smaller rooms, I often use a room fan to circulate air throughout the basement instead of letting it concentrate. And, if we've had a basement bathroom, I've run that bathroom exhaust for a period of time during and after tub use.
    While we've never had problems running during the drier months, I would recommend a bathroom exhaust fan in the near vicinity of the tub (and on a timer), even if you don't inform your building department or electrician (that installs your dedicated circuit) that you're putting a hot tub indoors. IIRC one electrician said that a vent fan was required, but I accidentally forgot to investigate that code requirement(?)

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