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  1. #1
    Join Date
    Dec 2009
    Posts
    4

    Humidity problem and Ultra air 90

    I have a one year old house on a crawl space that is lined with plastic. The indoor humidity is 60-70%. Have a central heat and air unit outside, gas heat, electric air, ducted through crawl space. I live in TN where it is humid. A Ultra air 90 whole house dehumidifier has been recommended. My concerns are that this will be placed in the crawl space and I am concerned about mold growth on the coils of the unit. Has this been a problem with anyone else? Also, the diagrams for installation show a return from inside the house with what appears to be a grill and filter like a normal return for CHA unit. A person I spoke with said all that was needed was an eight inch opening cut into the floor? But this is not what is shown in the diagrams from Ultra air website? But again I am really concerned about mold growth on the coils of the unit placed in the crawl space. Any help appreciated.

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  2. #2
    Join Date
    Oct 2009
    Location
    Murfreesboro, TN
    Posts
    108
    In middle TN we put these in crawlspaces all the time. Climate data backs up the need for more humidity control inside a home or office than an air conditioning system alone will provide. In most areas in the south the number of hours per year when a home requires cooling is less than the number of hours that dehumidification is necessary. Dehumidification demand is the number of hours in a year the outdoor temperatures are between 60 degrs and 75 degrs and dew point is 60 degrs or higher. Air conditioning demand is the number of hours in a year the outdoor temperatures are above 75 degrsF. That means around here dehumidification is necessary twice as many hours as cooling only. I like ventilating dehumidifiers that lets in fresh air through a motorized damper and lets some of the dry air into the sealed crawl space. You control the damper to meet your comfort needs.

    The condensate drain in the DH90 is designed so that water will not accumulate in the condensate pan. Just make sure the drain from the pan has a good slope to the outside after the P-trap. Besides, if you keep the crawlspace dry mold won't have a chance.
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  3. #3
    Join Date
    Apr 2002
    Posts
    11,808
    i only heard of one problem job where a thermastor product was a mold incubator
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,595
    Any syrface that has significant condensate flowing washes the spore and dust down the drain. Surfaces that are continuously damp and have dust collect will grow mold. If you want minimize the mold growth, operate the fan on the dehu continuously. This will dry the entire dehumidifier when not dehumidifing. Ideally, provide a 6"fresh air inlet with an 8" supply and return according the illistrations. Level the unit for good draining. 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"

  5. #5
    Join Date
    Dec 2009
    Posts
    4
    Thanks for the information. Will start getting quotes for Ultra air 90 and installation.
    Am new to this forum. Will post new question concerning cost.

    Thanks

  6. #6
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    Ideally, you need to dehumidify the crawlspace. Whether through A/C and/or a central dehumidifier. In the heating season, about 30% of the air in a home comes through the crawlspace. Bathroom fans and portable dehumidifiers can't keep up. Central dehumidifiers should be able to handle it. But why not attack the source and dry out the crawl space.

  7. #7
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    Teddy Bear, can central dehumidifiers be set up with a 30 or 60 second fan off delay after desired humidity has been reached?

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,595
    Quote Originally Posted by Baseboard Gord View Post
    Ideally, you need to dehumidify the crawlspace. Whether through A/C and/or a central dehumidifier. In the heating season, about 30% of the air in a home comes through the crawlspace. Bathroom fans and portable dehumidifiers can't keep up. Central dehumidifiers should be able to handle it. But why not attack the source and dry out the crawl space.
    The dew point of the a sealed crawlspace is determined by the outside dew point. As the outdoor dew point goes below 50^F, there is no moisture load from the crawlspace. A dehumidifier is seldom needed when you are heating the home. Indoor moisture is better reduced with proper fresh air ventilation. I would not attempt to control moisture in a crawlspace that was not sealed with plastic on the earth and the vents closed. 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"

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,595
    Quote Originally Posted by Baseboard Gord View Post
    Teddy Bear, can central dehumidifiers be set up with a 30 or 60 second fan off delay after desired humidity has been reached?
    Currently, we do not have a delay on the fan after the dehumidifier shuts off. The fan is shut off after dehumidifier operates unless constant recirculation is set up or if the ventilation timer call for fresh air ventilation. Using a time delay could be added that could interupt recirculation or fresh air ventilation. 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"

  10. #10
    Join Date
    Nov 2008
    Location
    Houston, TX
    Posts
    77
    I definitely agree on sealed crawl spaces. Same with plastic on the Earth. And sealed plastic at that. Even a small opening where the plastic is attached to the wall makes things worse.

    Back in my pre-Humidex days (pacific northwest), I would run a portable dehumidifier in the living area most of the winter. During the summer, windows were wide open. Summer air was dry enough (25-35%) that no dehumidifying was needed.

    But even with low dew points outside (outside temp below 50°F), that crawl space would still be damp even with sump pump, sealed plastic, vents closed. Attacking the crawl space humidity issue made the living areas upstairs tremendously drier. Much more so than leaving all 3 bathroom fans on all day long or a bathroom window open during the winter would.

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