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Thread: Dehumidifier

  1. #1

    Dehumidifier

    I bought a new house a few weeks ago had a new HVAC 13 Seer York installed. The house is 1800 sqft 4 bdroom 2 bath. I purchased a 70 pint dehumidifier and ran it for over 48 hours straight. The humidity level keeps showing 65 which I thought was high. I live in East Tennessee where the climate is mostly mild. The basement doesn't feel musty or wet. Should I just use a fan instead of the dehumidifier. I don't feel like the dehumidifier is doing anything.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Your dehumidifier should remove 30-50 pints of water per day at 65%RH.
    Today east TN has an outside 32^F dew point which infiltrates your home. You add moisture from occupants to air inside your home, you end up with a moisture level above the outside dew point. Most experts suggest an air change in 4 hours when the home is occupied. This would be 70 cfm of fresh air when the home is occupied. With adequate fresh air change to purge indoor pollutants and renew oxygen with a couple of occupants, expect 48%RH at 68^F. In a cold basement, raise the %RH 2% for each degree below 68^F. More fresh air lowers the %RH as does fewer people, low outside dew point, or warmer temperatures.
    Suggest that the dehumidifier should only be used when the outdoor dew point is +55^F. High indoor %RH during low outdoor dew points indicates inadequate fresh air ventilation. More fresh air ventilation is needed to reduce indoor %RH of a heated home.
    Of course all of this dependent on the accuracy of your %RH meter. Put your meter in a zip lock with a cup with wet salt, should read 75RH.
    If your meter is right, you have a tight home that needs fresh air ventilation during this kind of weather.
    Get your dehu working or your meter recalibrated. You will need it when the outdoor dew points rises next week. I like the new ventilating dehumidifiers like the Ultra-Aire, a sponsor of this site. These units bring the right amount of filtered fresh air when the home is routinely occupied. When the needed fresh air is damp and the a/c is not running enough, this unit dehumidifies the home.

    Turn off the dehu. Right now operate a bath fan until the %RH declines to your likes. Keep us posted.
    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"

  3. #3
    Join Date
    Sep 2002
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    Ventilation does a better job of controlling humidity when it's cold and dry outside than a dehumidifier can, at a fraction of the cost.

    Save the dehumidifier for summer - after a couple of years you may not need it.

    It takes a while for the building materials to dry out; new concrete holds a lot of moisture.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  4. #4
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by amd View Post
    Ventilation does a better job of controlling humidity when it's cold and dry outside than a dehumidifier can, at a fraction of the cost.

    Save the dehumidifier for summer - after a couple of years you may not need it.

    It takes a while for the building materials to dry out; new concrete holds a lot of moisture.
    I agree with the idea that adequate fresh air for good indoor air quality will keep a home dry when the outdoor dew point is <55^F.
    How does +60^F outdoor air keep the home dry after the house dries out without a dehumidifier??
    Its 70^F outside and raining, with 60 cfm of 70^F dew point fresh air, plus the occupants are adding 1 lbs. per hour, what is the %RH inside the home without a dehumidifier?? One other question, how much moisture must be removed per hour to maintain <50%RH at 73^F??
    This is a real problem.
    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
    Sep 2002
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    Solution: Use one when the dewpoint is above 55F as needed, if it's needed (musty smell, discomfort) - otherwise don't.

    Every application is different.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,592
    Quote Originally Posted by teddy bear View Post
    I agree with the idea that adequate fresh air for good indoor air quality will keep a home dry when the outdoor dew point is <55^F.
    How does +60^F outdoor air keep the home dry after the house dries out without a dehumidifier??
    Its 70^F outside and raining, with 60 cfm of 70^F dew point fresh air, plus the occupants are adding 1 lbs. per hour, what is the %RH inside the home without a dehumidifier?? One other question, how much moisture must be removed per hour to maintain <50%RH at 73^F??
    This is a real problem.
    Regards TB
    Solution: Use one when the dewpoint is above 55F as needed, if it's needed (musty smell, discomfort) - otherwise don't.

    Every application is different.
    AMD

    I agree again. The part that is missing is that:
    Adding one lb. of moisture from the occupants per hour to 60 cfm of 65^F dew point fresh air elevates the inside dew point to 71^F. The long term results is 87% RH air inside the home. Having a dehumidifier remove the 1 lb./hr of moisture from the occupants and 1 lb/hr from the fresh air result is a 55^F dew point or 50%RH in the 75^F home. Using this strategy, I have dehumidified +20 gals. of moisture during the month of March in WI to maintain 50%RH in my basement. Nothing in April. The point is that the outdoor dew point in green grass climates is +60^F much of spring/summer/fall. Your concern is based on individual needs. Some take what you get, a couple days of +65% RH will not hurt. A week or two will make your basement musty. A couple months grows dust mites in your bed. Fussy occupants or dehumidifier salesmen want to maintain <50%RH throughout their homes.
    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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