Indoor Spas - humidity mitigation

What are your best solutions for humidity and moisture concerns with spas installed indoors.  And, have you found different challenges depending on where in a home the spa is installed; i.e, in a basement vs in a sunroom; above grade vs.below grade, etc?

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  • Thanks, Shaun.  Very helpful! 

  • This is what we use for indoor pool/spas.  It can work as a new install or a stand alone unit.

    http://www.thermastor.com/HI-E-DRY-100/

  • Thanks!

  • No, I don't do installations.  I was just giving you an idea of how much water would evaporate from the spa if you kept it uncovered.  If you know the spa's surface area, then you can calculate how much water is in about 1/2" of depth to figure that much water that needs to be removed from the air per 24 hours.  In practice, the spa isn't always kept at 104ºF, but it at least gives you a rough idea.  A 6'x6' (interior dimensions -- roughly 500 gallon if 2' avg. depth) spa would be about 11 gallons of water per 24 hours.  Dehumidifiers are typically rated in pints per 24 hours so that would be 88 pints per 24 hours.  This is likely to be conservative since the spa isn't likely to be kept at such a high temperature the entire time.  Of course, during spa use with jets, the rate of water vapor introduction will be higher, but that should not be for very long.  Note that keeping the water at around 90ºF would evaporate 40% less so around 50 pints per 24 hours.

  • Have you had any success with interior basement installations?

  • The evaporation rate from the spa will depend on the water and air temperatures, the humidity of the air, and the amount of air movement (wind).  If I assume 104ºF spa water temperature, 72ºF air temperature, and no wind, then the evaporation rate is 0.43" to 0.68" per day depending on humidity.

  • Thanks to all so far.  Was in ACY the last few days.  The most consistent advice seems to by cover the spa when not in use (of course) and possibly extraction fan/dehumidifier combination.  There's some thought that a spa produces about as much water vapor in a half hour as a shower produces in five minutes.  If that's valid, seems a good HVAC person could help.

  • I would recommend the use of HeatsavrTM a liquid pool cover produced by Flexible Solutions, Canada.   Heatsavr is particularly helpful in the case of irregular shaped pools.    Heatsavr when used will give you savings on water and air heating and reduce humidification and evaporation.   For further information visit these links http://www.heatsaver.co.uk/indoor.php and http://www.flexiblesolutions.com/products/heatsavr/testimonials.shtml

    Heatsavr
  • This is an engineering problem and is usually beyond the capabilities of just an AC guy, You must cover the spa when not in use. I use dessert air systems, and good ventilation the cost of moisture damage will quickly outweigh the cost of a good system. 

  • I am in the same situation. I am involved in a project that will have a therapy spa inside of a doctors office. I have an AC general contractor involved to control the humidity, but the costs seem rather extreme. Is there a formula that we can go by as a guide to calculate how much water and humidity will be created based on several factors -

    1) air temperature

    2) water temperature

    3) water evaporated?

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