High humidity problem
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  1. #1

    High humidity problem

    Can someone please help? I am a small project remodeler who is having a humidity problem in my own home. It has been happening for about 6 years now and I am losing hope that this problem will be solved. I live in Northwest Arkansas. I don’t know of anyone else having the same problems, so I can’t blame it on the weather around here like you might be able to in a more tropical location. None of my neighbors are having the same trouble although they have been dealing with some of the same water issues that I have. I have had probably 30 people try to help me solve this problem, have spent more that $20,000 in “improvements” and only one thing that has done ANYTHING to decrease the humidity is to seal some air leaks between the house and the crawl space. Installing the new windows seemed to increase the humidity a little, although I am unsure about that because I can’t find my records at this point. I know that it did not help any. I do NOT want to run a dehumidifier. I’ve been doing that. I want to figure out what the problem is and fix it.

    Humidity is fine when A/C is not needed. As soon as the A/C is needed (temps over 75 for me), humidity shoots up to between 58% to 65%. I have set the A/C at different temps in order to change the humidity level without much success unless I crank it down to something like 62 degrees and it runs continuously. I like it cool in the house and have to have it cool to sleep well. I am having to set it at 67 degrees at night to be able to be somewhat comfortable, but have noticed that I am REALLY comfortable at other people’s houses when it is set at 70 degrees. The air in my house is noticeably damp and mildew is a problem.

    The blower motor was replaced sometime near the time of the start of the humidity problem. I can’t remember if it was before it started or after and it’s been checked out by four A/C contractors and found to be working properly. I had someone go into the attic and open the unit to check the temperature of the coil, it is running at the correct temps too (~46 F).

    House info:
    My house is about 1,900 s.f. with a Carrier 58RAV095-16 furnace and a Carrier CK5BXA042000ABAA A/C unit installed in 2000 which replaced a unit of the same size.
    House was built in 1965
    Moved into the house in 1998
    Mildew in bathroom cabinets and den cabinets when I moved in.
    Rest of house fine and humidity levels fine until 2003
    Attic is vented with ridge vent, three gable end vents, soffit vents, and two passive roof vents
    Crawl space is vented with 8 vents
    The construction and ventilation is the same as all the other house built around here at the time. Not many places around here have a closed/unvented crawl space. Currently houses are being built with vented crawl spaces.

    Things done to try to fix humidity problems:
    Moved ductwork and furnace unit to attic from the crawl space and had it tested for air leakage with blower door test. The existing ductwork under the house was disconnected somewhat in places which I am sure contributed heavily to the beginning of the problem. (I had paid two different companies to check my ductwork, “repair” it, and reinsulated. Neither did anything past the first 15 feet or so. I am claustrophobic and did not check their work.)
    Had gutters put on the back of the house
    Had a French drain installed along full length of back of house last summer because my backyard slopes toward my house and water pooled against it until it drained. Have not been able to find anyone to check under the house to see what the condition of the dirt is at this point, but will soon hopefully. I know that it is working some though as the door to my bathroom shuts all the time instead of some of the time (i.e. no house movement due to clay swelling.)
    Put new 6 mil vapor barrier under house
    Sealed all under house leaks between house and crawl space, sealed all floor vent holes.
    Sealed hole in bathtub drain
    Installed energy efficient vinyl windows w/ LowE glass to replace single pane aluminum windows w/ storm windows
    Sealed around vents from house to attic
    Air handler blower motor speed has been adjusted to try and pull more humidity out.
    I have been able to rule out laundry and showering as major contributors to the problem as I didn’t live in my house for almost a year due to an injury and I still had humidity problems just as bad as in the past. Also, I live by myself, so it shouldn’t be a big issue anyway. The folks next door are a family of five and don’t have any issues.

    Changes in house besides those listed above:
    Added 10 inches of cellulose insulation to attic.
    Replaced all flooring, went from carpet throughout house to tile, wood, and laminate
    Added more attic venting. Previous was two gable vents and two whirly gigs on the roof.

    The humidity and temperature readings are based off of Radio Shack digital humidity and temp gauges.

    If anyone can provide steps to take, tests to do, measurements to take, I would be glad to do that. If there are multiple steps or measurements to take, please list them all together because I will probably have to borrow equipment or have someone else do them due to lack of equipment or inability to access attic or crawl spaces by me (injury and claustrophobia.)

    Thanks for any help you can offer!

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,274
    During the day, what do you keep the thermostat set on? During the day, what is the cycle rate of your a/c? Meaning how long does it run, and how long does it stay off between run times?

    I have had probably 30 people try to help me solve this problem, have spent more that $20,000 in “improvements” and only one thing that has done ANYTHING to decrease the humidity is to seal some air leaks between the house and the crawl space. Installing the new windows seemed to increase the humidity a little, although I am unsure about that because I can’t find my records at this point. I know that it did not help any. I do NOT want to run a dehumidifier. I’ve been doing that. I want to figure out what the problem is and fix it.
    I noted where you have plastic over the soil in your crawl space. Consider the next step and go with a non ventilating crawl space. This hinges on the barrier you installed being installed well with all seams taped.

    Think about this. You're trying to ventilate a humid area with humid air. That is what ventilating a crawl space in summer amounts to. You also bring wind into the crawl space via the ventilating screens and pressurize that space on the windward side, depressurize it on the lee side, with that pressurization being far from equal. Translation: said pressurization can find air leakage routes into your house that you can't imagine are there. Get rid of the wind, get rid of the pressurization.

    Building air leakage can account for up to 40% of all heating and cooling costs. In humid climates it adds a tremendous dehumidifying load to a/c systems.

    Not to ignore your a/c, either. If it's not sized correctly, or if it is and it is not tuned correctly, it won't perform the way you need it to.

    When you mentioned having a blower door done on the relocated a/c and ducts, what was the result of that test?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


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  3. #3
    Thank you so much for your time and experience. I'll do my best to answer all of your questions.

    During the day, what do you keep the thermostat set on? During the day, what is the cycle rate of your a/c? Meaning how long does it run, and how long does it stay off between run times?
    For the first half of the month, I had it set on 70 degrees, 24/7. For the last week or so, on 68 except for when I pushed it down to 62 yesterday. It emptied the house of a lot of moisture, but the humidity was back up this morning. It turned the thermostat back to 68 before I went to bed.

    I have had a hard time figuring out the cycle rate, but my brother just gave me an idea that I am going to try. I have a hard time paying attention to when the A/C kicks on and off. He suggested putting something that would really rattle up near the vent which would make more noise and catch my attention. How many cycles do I need to count? Just one or do I need to do more and average them?

    I noted where you have plastic over the soil in your crawl space. Consider the next step and go with a non ventilating crawl space. This hinges on the barrier you installed being installed well with all seams taped.
    That is a possibility, but the lowest cost quoted me is more than $5,000 and I am not planning to spend major money until someone can guarantee that this will solve the problem. Do you have suggestions for testing that that are quick and cheap? Like maybe putting high powered fans at two vents to suck the humid air out from under there? Again, not many, probably less than 2% of the people around here, have sealed crawl spaces and I know of no one else having this trouble. Also, this house did not have that trouble until about 6years ago. I know of one woman that frequently has standing water under her house and her humidity is much lower than mine.


    Forgot to put in the first post that my current A/C guy brought a thermal imaging gun here and we looked at each room which helped us to spot air leakage. There was some around windows and doors and a few pipes, but I have had new windows installed and added more weatherization to the doors and have caulked and foamed around the pipes.

    The plastic barrier was installed well and only has one seam which is triple taped.

    What are your thoughts on spraying insulating and water-blocking foam onto the underside of the floor and along the sill plate? That is something that is done in some parts of the country.



    Not to ignore your a/c, either. If it's not sized correctly, or if it is and it is not tuned correctly, it won't perform the way you need it to.
    Can you tell based on the model numbers I gave on my first post what size unit I have? I think I recall that it is a 2 or 2 1/2 ton. I have had the unit looked at by four different A/C companies and all have pronounced it good. I followed all of them around and asked a lot of questions and they all had the same results.

    When you mentioned having a blower door done on the relocated a/c and ducts, what was the result of that test?
    I can't recall. The test happened just before a surgery I had and I lost a lot of memories I had stored. I know that the man was impressed that the results were so good even with my leaky windows. I will try to get that info on Tuesday if I can get in touch with him.

    I am getting ready to leave the house for a few hours, but will check back as soon as I can. Thanks again for your help.

  4. #4
    Join Date
    Dec 2010
    Location
    Palm Beach,Fl.
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    947
    The A/C is 3.5 ton, not sure about the furnace, i'm gonna guess its a 95000 BTU,seems the blower might be slightly oversized but not enough to cause such poor humidity control

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,274
    Widgetwilson, two things stood out for me from your OP.

    This:

    The blower motor was replaced sometime near the time of the start of the humidity problem. I can’t remember if it was before it started or after and it’s been checked out by four A/C contractors and found to be working properly. I had someone go into the attic and open the unit to check the temperature of the coil, it is running at the correct temps too (~46 F).
    I would want to know if the new blower motor that was installed was of the same specification as the motor that died (provided the original motor was the one that came with the unit when it was new). I would also want to know if the replacement motor was set on its highest speed after being installed.

    If the motor is on its highest speed setting, it may be moving too much air to serve your dehumidifying needs. You stated elsewhere you need to really push your thermostat down to keep the unit running. On one hand this could be a sign the unit is oversized. On the other hand it could mean the unit still may be oversized but can perform better at a lower blower speed pertaining to dehumidifying the air in your house.

    The other standout from your OP:

    and only one thing that has done ANYTHING to decrease the humidity is to seal some air leaks between the house and the crawl space.
    There are two ways to reduce high humidity levels inside of a house. Reduce how humidity gets in or increase how it can get out. What you're stating above is you noticed a decrease of humidity getting in after you performed some sealing between the crawl space and the house. What may have not yet been addressed is increasing the rate of yet remaining levels of humidity in the house out, to where you're comfortable.

    That you replaced windows in hope of solving this problem is only unfortunate from a humidity management issue. Yes, your old windows leaked, but without understanding what drives air leakage into and out of houses in summer, you're only swatting at flies, not creating a way to keep flies out of your house altogether.

    The way I see it, the truth is your house has had humidity management deficiencies all along. It was only when your blower motor died and was changed that you noticed it. I would step back to that day and see what was changed from the old motor to the new one. It may be set on high speed when it should be on medium-high or medium.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Thank you both for your replies.

    The blower motor was checked by two of the A/C people for correct match to existing unit at my request. They both had the opportunity to make money by telling me it was the wrong one, but did not.

    The fan speed has been adjusted to different speeds to see if it would help. No noticable difference. I believe it is set the lowest speed currently. That change happened last week.

    Again, I would like to ask if there is a way to cheaply, easily check to see about testing whether or not the crawl space is contributing significantly enough to the problem that it warrants the extra money to either shut it off or foam it?

  7. #7
    Oh, forgot to add that the window replacement was not totally due to the A/C problem, but we hoped it would help some. My energy bills have dropped considerably. So not a loss from that standpoint, but I probably would have not done it at this time if I had not been told by several folks that they thought it would help.

  8. #8
    Join Date
    Jan 2008
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    1,948
    If the unit is over-sized, upgrading the windows could add to the high humidity problems.
    Sounds like your system is too big, runs short cycles, and can't de-humidify, due to short run times.
    Fairly common problem.
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  9. #9
    Join Date
    Jan 2004
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    Lancaster PA
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    You may have had new windows installed. But, what says they were installed correctly that you don't have moire infiltration from the new windows then you did from the old windows. Next, with all of the improvements you made, your A/C may be very over sized, and cooling the house too fast to remove enough humidity.

    To easily test your crawlspace. Put plastic over any openings you can see. Then put your portable dehumidifier down in it, and see how your humidity is in a couple of days.
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  10. #10
    Thanks for your replies.

    The cycle time is 8 minutes running, 12 minutes off.

    That's with the temp set at 68%. Humidity is at 61 percent.

    67 dewpoint outside, 79 degrees, humidity is 58%.

    I feel that the windows were installed properly and the air leakage is much less. I used to not be able to sit on my couch without a jacket on during the winter and this winter I barely noticed a difference whether I was in the middle of the room or right next to the window. I'm pretty sure that if they leaked more than the old ones, my bills would have been higher, not much lower.

    I will try the test you mention if I can find a dehumidifier that will fit in the crawl space. Not sure I can find one around here. Would blocking the vents and putting two fans at opposite sides of the house facing out do any good? I have those things available to me.

    Is there any solution to an oversized unit other than replacing it?

    Again thanks for your time, everyone!

  11. #11
    Join Date
    Jan 2004
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    Lancaster PA
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    No, the fans either won't exhaust any air with the vents closed. or will cause fresh air to be drawn into the house, giving you no usefull info.

    8 minutes on, 12 off set at 68, sounds very over sized.
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  12. #12
    Join Date
    Mar 2009
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    Southeastern US
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    I agree, based on the short cycle times, it sounds like the unit is over sized... I would have the HVAC contractor perform a manual J load calculation to account for all of the improvements. If it is over sized, replacement is the right way to go.

  13. #13
    Join Date
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    This is a mess, open vents on a crawlspace, negative pressure in the attic, fan-"on" mode, and no idea of the a/c coil temperature. You have the possiblility of sucking large of amounts of high dew point outside air into the home.
    After fixing all of the above and adding a whole house dehumidifier, you can maintain <50%RH during all cooling load conditions.
    Without the dehu, you will not be able to maintain <50%RH when the outdoor dew point in +60^F and low/no cooling load. Most live with occasional high humidity. Mold grows with +24 hours of high indoor humidity.

    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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