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  1. #1
    Join Date
    May 2004
    Posts
    2
    I'm an duct installer, and at my own home we have been doing some work and cut in a attic drop down staircase and a new electrical service from the attic. Now I have mold and moisture on the walls in the areas we are working. does anyone have a idea of a way to test.

    thanks

  2. #2
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    get an %RH meter from a reptile pet store ~$10. Keep RH below 60%, the lower, the better.

    Add insulation & weatherstripping to drop- down steps. You could also seal off the attic vents to keep humidity from attic.

  3. #3
    Join Date
    May 2004
    Posts
    2
    Thanks alot, I thought it would be the attic insulation, at times the cieling and walls sweat. Someone told me once to run the AC as cold as it could get to remove the moisture..... is that true????

  4. #4
    Join Date
    Apr 2002
    Location
    Texas
    Posts
    165
    Originally posted by cgross
    Thanks alot, I thought it would be the attic insulation, at times the cieling and walls sweat. Someone told me once to run the AC as cold as it could get to remove the moisture..... is that true????
    Not necessarily. Every degree downward the thermostat is moved increases the RH% by 2 points.

    Check it out with a psyc chart for your acturl conditions.

    Frank

  5. #5
    hey it is all relative 39% humidity can be high relatively and 70% can be low relatively

  6. #6
    It would do your home a lot more good to keep the fan running constantly to keep the moisture from collecting. The air changes will help to drag the moisture out and keep the RH down more than trying to cool your place down to 68 degrees, which will only increase your electric bill and create more moisture along the exterior walls. And make sure your moisture barrier has been installed correctly.

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,063
    Originally posted by marauderx
    It would do your home a lot more good to keep the fan running constantly to keep the moisture from collecting. The air changes will help to drag the moisture out and keep the RH down more than trying to cool your place down to 68 degrees, which will only increase your electric bill and create more moisture along the exterior walls. And make sure your moisture barrier has been installed correctly.
    Not sure what this means. The air changes will help drag the moisture out. Where should the moisture barrier be?

    Dry wall on the ceiling below attic has outdoor dew point on the attic side of the drywall. The house temperature is on the inside of the drywall. Laying fiberglass insulation on the top of the drywall helps the drywall cool down to the temperature of the home. But the dew point of the air is high in the attic and in the insulation. Like a cold can of pop from the refrigerator, moisture condenses on the drywall when the temperature of the drywall is below the dew point of the air. Makeing the house colder makes the drywall colder and sweat more. Two choices warm-up the drywall or lower the dew point of the air exposed to the cool drywall.

  8. #8
    Join Date
    Apr 2002
    Location
    Texas
    Posts
    165
    I don't know what the climate in Rome, GA. is, but if it is hot/humid, I would not suggest that the fan be left in the constant "ON" position. U. of Florida expermented on this and determined that "ON" caused the mositure to evaporate off the coil and raise the humidity in the facility.

    This will cause mole growth.
    Frank

  9. #9
    Originally posted by Frank_G

    This will cause mole growth.
    Frank
    Heheh...pesty rodents...

    Frank: the coil was removing far more water from the air than adding. The problem was they did not specify a bypass for the larger commercial equipment that was studied.
    ...
    The air changes increase the amount of moisture that can be evacuated from the space. If the air you are pushing through is drier than the air in the space (around the same temperature) it will add itself to the air before being removed from the space, taking the moisture with it. If the air to do this is partly taken from outside air and the OA has a high RH%, the cooling coil should be run to squeeze the moisture from that air before applying it to the space to be balanced. The RH% of the lower temperature supply air will probably be higher, but once mixed with the room air it will lower the overall room RH%. Lowering the supply air temp increases the difference in how the air will perform to remove the moisture. The instinctive choice would be to run cooling for as long as it takes to remove the moisture at the coil and let the room air DB temperature drop as well. If you look at a psychrometric chart you can see what happens to the RH% - it goes up. However, the amount of moisture in the air drops too. Where does it go? Into your walls, furniture, insulation, anywhere but the air. Not good. On top of that, your cooler interior may have shifted it's dew point (as per teddy bear's post) to allow condensation to occur where you don't want it. Even worse.
    Instead run the cooling coil as you would normally to cool the house to a comfortable level. When you are gone on vacation for two weeks, run the system like you were there once in a while to prevent mold growth.

  10. #10
    Join Date
    Apr 2002
    Location
    Texas
    Posts
    165

    Boy . . . Do I feel Stupid!

    I read your post three times and still don't understand what you said!

    I still feel that one should not run their fan in the constant "ON" position in a hot/humid climate, I have seen first hand the results, and the study I referred to is on residential split systems.

    Please break your statement down such that one as poorly educated as I can understand what you said.

    Frank

    P.S. Yes those moles are pesty! I've tried to eliminate them in my yard but believe I'll have to call Bill Murray to do the job for me.

  11. #11
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    RE: moles: I will rent my cat, Sparky -- he spends hours hunting them!

    re: humidity problem: it seems to have started with new stairway? did you have scuttle hole there before stairway? seal off the stairway with plastic & duct tape for 1- 2wks -- if condition gets better, refer to my earlier recommendations.

    get a portable dehumidifier, place it in the utility closet ---

    what is your RH%? what is cfm during cooling? problem only ocuring with outdoor temp <85F? does your unit have too much capacity (= no dehum)?

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