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  1. #1
    Join Date
    Jun 2018
    Posts
    1
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    Ultra-aire question and dusty attic smell

    Hi all,

    I live in MD and recently purchased a new home. I started noticing a dusty, attic smell from the upstairs registers and during investigation noticed the elevated RH levels. I had an HVAC contractor out to see if there was mildew on the coils and they were clear and he confirmed the coolant pressure seemed appropriate. I'm thinking their must be a leak in the flex ducting in the attic or somewhere else attic air is getting sucked into the system.

    Otherwise, regarding the humidity issues...

    I'm having to set my thermostat to 69deg to get a comfortable temperature, upstairs and down. The is two stories with a basement, dual zoned with a furnace/ac for the basement/first floor and heat pump with blower in the attic on the second floor. 4,350 sq ft total (almost all finished) with two 3-ton units. Right now, during a long cooling run on a hot day, the lowest RH I've seen is 56% on the main floor and about 59% on the upper floor. As an example this AM when I woke up, the outdoor temp was 74 with RH at 92%. My upper floor was set to 69 and the RH was 70%...

    I'm assuming I need to have the fan speed reduced at a minimum IF the coils are truly cold enough (didn't really care for this contractor). I also am considering an Ultra-aire to help bring in fresh air and dehumidify.

    Once I get the system to cool appropriately during hot days, where should I place the Ultra-aire? I have not checked basement humidity levels, but there is definetley more room in an attic install on the upper system for the dehumidifier/fresh air.

    Any recommendations would be appreciated!

    -Blake

  2. #2
    Join Date
    Apr 2003
    Location
    St. Louis
    Posts
    639
    Post Likes
    Start with blower door test to see how tight the house is ( your electric company might have a energy audit mine does) At your outside temps how long does the cooling run or does it cycle alot?

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    8,746
    Post Likes
    Moldy smell in attic ducts could be a leftover from winter condensation problems. Cold ducts in the attic can have severe condensation while the attics are cold with exposure to home moisture levels. To avoid, the ducts must be kept warm enough to keep the ducts from extended wet days.
    Regarding location of an Ultra-Aire, the basement is the coolest space with the highest %RH. Draw air from mainfloor with supply to the a/c supply and to the basement with damper adjustment. An air change in 4-5 hours is suggested and maintain 50%RH throughout.
    A well built home with closed windows needs fresh air during the mild seasons of the year and occupancy. During winter, most homes get enough fresh air because of winds and stack effect.
    Keep us posted. Thanks for your interest in the concept.
    Regards Teddy Bear
    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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