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Thread: high humidity

  1. #14
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,451
    Originally posted by opti
    noticed a little mold/mildew around one of my vents, and tried to find a water leak. I couldn't find any, but while trying to diagnose it I noticed my humidity level in the house is pretty high - about 50-55%. I'm in Dallas, and the outside humidity is about 32% currently, but my inside humidity is about 55%. My system is 2Bryant 2.5 ton systems (zoned one per story), in a 2 story 2600 sq ft home. The house is about 5 years old. The humidity doesnt' really change much if I run the system for extended periods or just normally. I called a service company, they came out and did a check. They weren't real sure about the humidity, but they said that an issue I had was low air flow. They claimed for my 2.5 ton system I should be getting 1000cfm, they were only seeing 700. They said my 20x20 return with a 14" duct was too restrictive, and for $1000 they'll add another 2 10" returns to increase the airflow. They weren't real sure if this was my humidity issue or not, but felt that it would probably fix it. He said everything seemed fine across the coil, and that the CFM issue was the only real thing he could find. Of course, i'll get a 2nd opinion before committing to that kind of work on a fairly new system. Any ideas on my humidity problem? It's usually 34% or so at work with a pretty old system on 73 degrees. No matter what I set mine to I just can't get below 50%. I'm worried about mold issues, and why mine won't dehumidify in general. They lowered the blower speed from high to med-high to try and get it colder across the coil, but it didn't seem to help. I think he was saying because of the airflow issue he couldn't charge it as much as he thought it should be
    50%RH is acceptable for mold control. Occasional 55%RH is not a problem. 90^F, 40%RH is much wetter than 75^F,50%RH. Check for the ^F dew point or grains of moisture to compare moisture content. Dallas outdoor dew points about 70^F, inside should be 50^F. Sucking in hot outside 70^F DP air makes your house wet. Watch for rainy cool weather! the a/c does not run much and the home gets wetter. Slowing the air flow makes the cooling colder removing more moisture. Cold air makes the grills and drywall around colder, causing condensation from the surrounding humid house air. Clean the grill/drywall soap/water. If wet for several days, mold will return. There must be times when your home is wetter than 55%RH, like this spring. A/C removes 100 pints of water on hot day. On a wet cool day, only a fraction of the moisture is removed. A 100 pint whole house dehumidifier will maintain <50%RH without any a/c operation. We manufacture the Ultra-Aire and Santa Fe whole house dehumidifiers.
    Commercial buildings with internal heat gain from lights and equipment being cooled by near freezing cooling coils may provide lower relative humidity. RH meter are very inaccurate at very low or high %RHs.

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    I think theres a fee you have to pay for it to work.

    If your systems are over sized, it would be a replacement of the outdoor unit, and maybe the indoor unit.

    Has keeping the downstairs warmer made a difference.
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    How many times must one fix something before it is fixed?

  3. #16
    Join Date
    May 2004
    Location
    Indiana
    Posts
    48
    I am a homeowner not a professional but had very similar issues 2 yrs ago. Everyone on this forum helped us.

    My opinions...

    1. check duct work for leaks as a leaky supply will create negative pressure situation in your house causing outside air to be sucked in constantly (been there)

    2. get 2nd opinion on air flow problem, but i would think not enough air flow over coil would cause it to freeze up and you would see this on very hot days when it is running alot, esp. if set at 72. Do you see evidence of freezing up coil? (been there too)

    3. as teddy bear said, you cannot compare outside humidity to inside. 90 and 35% humidity is relative humidity, water in realation to temp. When air is cooled the relative humidity goes up, because warm air holds more moisture than cool air.

    4. seer rating...I thought i remembered reading a couple of years ago that many professionals felt this to be a big issue with dehumidification...higher the seer, less ability to dehumidify?? (been there also, I thought)

    5. I too live on a slab. Have no idea if this contributes, but have to wonder.

    6. We learned that it paid off for us to monitor RH in our home year round!! If humidity gets high, everything in your home holds the humidity. We could feel it in our carpet. We purchased a standing dehumidifier, and run it to keep humidity below 50%, ideally 45%. Whole house ones were too expensive for us. We run it in spring when a/c does not. We run it nightly since a/c does not run much at night, and keep house temp at 75.
    Its perfect!

  4. #17
    Join Date
    Jun 2005
    Posts
    9

    .

    Thanks guys. I have the downstairs at 77 and the upstairs at 72, it's been keeping the upstairs running pretty long, but I haven't seen much of a difference. How do I check for duct leaks? I know I have a problem with my backdoor. It doesn't have any porch/ or covering at all, and the builders did a crappy job, I think the trim and frame is more caulk than wood. It's a terrible fit, and not sealing at all. I have someone coming to replace the door and repair the frame next week. Per a suggestion here I stopped by Sears to get a 50 pint dehumidifier. Salesman was pretty shocked, they don't even carry them in store here because they don't sell any. It should be here Tuesday. Is that little guy going to be able to help the whole house, or am I going to need one per floor? Right now according to my Radio Shack atomic clock/weather station it's 48% uptsairs and downstairs, but my Radio Shack little digital hygrometer I had for my cigar humidor is reading 52%. This is with all my exhaust fans (2 downstairs, 3 upstairs) running since yesterday morning.I hope the weather station is more accurate . It's usually lower like this in the morning, then climbs during the day. I emailed off for pricing on the Ultra-Aire, but I have a feeling it's out of my price range. I'm really hoping a cagey AC vet can do some magic and wrangle some more dehumidification out of my AC. The problem seems to be finding one.

  5. #18
    Join Date
    Jun 2005
    Posts
    9
    Originally posted by hvac_help_needed
    I am a homeowner not a professional but had very similar issues 2 yrs ago. Everyone on this forum helped us.

    My opinions...

    1. check duct work for leaks as a leaky supply will create negative pressure situation in your house causing outside air to be sucked in constantly (been there)

    2. get 2nd opinion on air flow problem, but i would think not enough air flow over coil would cause it to freeze up and you would see this on very hot days when it is running alot, esp. if set at 72. Do you see evidence of freezing up coil? (been there too)

    3. as teddy bear said, you cannot compare outside humidity to inside. 90 and 35% humidity is relative humidity, water in realation to temp. When air is cooled the relative humidity goes up, because warm air holds more moisture than cool air.

    4. seer rating...I thought i remembered reading a couple of years ago that many professionals felt this to be a big issue with dehumidification...higher the seer, less ability to dehumidify?? (been there also, I thought)

    5. I too live on a slab. Have no idea if this contributes, but have to wonder.

    6. We learned that it paid off for us to monitor RH in our home year round!! If humidity gets high, everything in your home holds the humidity. We could feel it in our carpet. We purchased a standing dehumidifier, and run it to keep humidity below 50%, ideally 45%. Whole house ones were too expensive for us. We run it in spring when a/c does not. We run it nightly since a/c does not run much at night, and keep house temp at 75.
    Its perfect!

    How big is your home, and how big is your standing dehumidifier?

    What do I look for to see if my coil is freezing?

    for my SEER rating, not sure. It's a Bryant 2.5 ton , outdoor piece has a model # 563cn030-B. There's no marking on the inside unit other than Bryant, but a sticker on the big box piece taped to the furnace has a label- 'Allstyle Coil " mode # ASFW363622T, 300psi R-22.

    Now, on the warm air/cold air humidity thing . What's the ideal temp/humidity indoors? I can get the temp from 78 to 72 and the humidity doesn't seem to change much if at all. Time of day seems to make more difference than anything. It's usually just under 50% in the mornings, and climbs to 52-53% throughout the day. 74 is about the most comfortable for us, but I'll go up or down a bit if that helps at all with moisture content.

  6. #19
    Join Date
    Jun 2005
    Location
    Clearwater,FL.
    Posts
    34
    50% RH - 60% rh is good ,working in the most humid tpabay area & seeing loads of mold & mildew calls,what you describe is not humidity problem if your house is tight & closed up all the time, you can't expect the same outside as inside,your lower than normal airlow will actually perform better dehum(though a problem).call a reputable co. and try to get a lead tech out to make sure you have clean coils-blower proper metering device if piston,proper superheat& subcooling,airflow. if they are clueless about or can't test humidity or anything listed here, give'm the boot!expect a 1-2hr. service call for the 2 systems.

  7. #20
    Join Date
    May 2004
    Location
    Indiana
    Posts
    48
    opti

    our home is almost 3000 sq ft. It is a 2 story, with 2 rooms with 2 story ceilings, one room with cathedral ceiling, and 9 ft ceilings entire 1st floor so there is alot of cubic air.

    our dehumidifier is a 70 pt. standing purcgased from sears for about $200. Basically we run it when we know the cooling is not going to run as much, like nightly, and when weather is cool and damp like early spring.

    We knew our coil was freezing because you could see the condensation leaking from the bottom of the furnace when the a/c shut off and the coil began to thaw!

    I do not know much about Bryant systems. And I just threw the seer point out there to see if any others in the field would elaborate.

    As for temp/humidity, it is a matter of personal preference, but anything below 48% rh in my home feels good. I try to keep it 45-46% by running dehumidifier at nite and a/c during day. 75 and 45% rh is extremely comfortable. I have been told by many respected service people that 60% rh is common in homes in summer, and some service people feel that should be tolerated.

    I do not understand running your exhaust fans. This creates a negative pressure situation in your home, and in order to equalize the pressure, outside air gets sucked in, creating more humidity issues. I would turn them off.

    I find it interesting that your humidity increases throughout the day...mine is opposite. But I do recall this happening when our coil was freezing up....as it thawed it basically acted like a humidifier as air blowing across it dried it and blew moisture back into the house. Are you running the fan in the ON position?

    [Edited by hvac_help_needed on 06-28-2005 at 07:08 AM]

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