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HVAC won't remove humidity

I have been our school librarian, in the same room, for several years.  Since August, I have not been able to get the humidity below 55% and the room smells like a musty cellar.  Our HVAC guy has been in here twice and recharged one of the units.  He says both units now are working, that since we live in a humid state, 55% is pretty good and smells can come from anywhere. He suggested I turn the thermostat down to 68 degrees to get the humidity out. I've tried to explain that it has never felt or smelled like this before. I finally purchased a temp/humidity gauge. At times the humidity has been as high as 72% with the AC keeping the room at 72 degrees. Currently, Classroom next door--75 degrees and 45% humidity.  Hallway that doesn't even have vents--75 degrees and 48% humidity. This library--68 degrees and 55% humidity. Part of the time, the humidity goes UP once the AC kicks on in the morning. Humidity in a library is never supposed to go above 50% because it affects the quality of the materials. I would like to stress that this is a NEW phenomenon. It has not been a problem until this year. Thanks for your ideas.

Re: HVAC won't remove humidity


55% humidity level is the normal for about 99% of the locations. There are a couple things that could be causing the problem for one room to be lower in humidity than others.

  • The AC unit is too large: If your air conditioner’s compressor unit is too big, it may be cooling the area too quickly. While this might not seem like a problem, if your home is cooled too quickly, your dehumidifier may not be able to keep up.
  • The dehumidifier is running too often: Sometimes the dehumidifier may run its cycle too often and result in ineffective dehumidification. If you suspect this is the problem, try resetting the humidistat and see if the moisture dissipates.

You may need to call in the professional HVAC company and speak with them about putting that area on it own. That way the AC can run to cool the air, while at the same time removing a larger amount of humidity, without affecting surrounding areas. Once a HVAC system is installed, it will take some time and adjustements to get everything set correctly. This could also include putting certain areas on their own controller. A good quality HVAC company will know this sort of thing and be able to correct this.


Handy Andy In Mt Airy NC

Re: HVAC won't remove humidity

Thank you for the information.  This room is on its own system and has the same two units that it had six years ago.  Each room in our building has its own unit and thermostat. The other rooms have lower humidity than this one, even when the temperature in those rooms is higher than the temperature in here.  If the units are the wrong size, I am wondering why this problem would just now arise when nothing else has changed  in the past several years. 

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