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  1. #1
    Join Date
    Jun 2004
    Posts
    2

    Question

    There is a sweet smell coming from a few of my air ducts when I have the air conditioning running. The smell is a very sweet almost syrup like smell. Any ideas on what it is and how to get rid of it. Or should I make a service call? ANY suggestions would be appreciated. Thanks!

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,644
    Mold and other biologicals generate various odors, some do not generate any odor. Keeping your ducts dry as possible limits the moisture necessary for biological growth. When the a/c operates, the %RH is high enough to grow biologicals. The a/c cycles on/off, leaving a water loaded coil in the air handler. Until the water on the coil evaporates, the ducts are wet in the off cycle. Operating the fan continuously would dryout the ducts in 30 minutes and stop mold growth in the ducts. If the odor goes away with the fan in the "on" mode, moisture and biologicals are probably involved. Unfortunatly, drying the ducts/evaporater makes your home more humid. Eliminating biological growth in duct may justify operating supplimental dehumidification to maintain <50%RH. Try the fan "on" and check the odor problem first.

  3. #3
    This wouldn't happen to be on a chilled water system would it?

  4. #4
    Join Date
    Jun 2004
    Posts
    2

    Hmm

    I'm not sure what you mean by "chilled water system". I do know that we have a heat pump and the entire system is a "RUDD" unit(residential). Could I be smelling Freon? What do you think?

  5. #5
    Join Date
    Jul 2004
    Location
    Houston Texas
    Posts
    17
    Serviceman1,

    Having a chilled water system would not make a difference. The dew point is still reached at the coil surfaces and condensation will form. Whether your cooling at the coil with chilled water or any variety of phase transitioning refrigerants, the end result will be the same; condensation will form on the cold coil surfaces and will have to be dealt with via the condensate drain system and re-absorption back into the air from whence it came. When the chilling stops and the coil surface temperatures come back up above the dew point, the RH in the airstream starts to rise as the water on the coil evaporates.

    If the blower is running all the time, it will accelerate the drying process and will dry the coil fairly quickly. This keeps the RH in the plenum and ducts generally lower after the cooling cycle but raises the RH in the living space by some small amount after the cooling cycle as the fan flushed that humidity out of the sysetm and back into the living space. Not running the fan all the time keeps the RH in the living space a bit lower but dramatically raises it in the ducts and plenum where the moisture evaporates into a smaller volume of basically stagnant air. That’s why supply plenums, coil cabinets, and the first several feet of ductwork exiting the plenums are such prime locations for fungal growth. The moisture issues in these locations are chronic by design and when a food source is also present, the development process for fungal growth begins.

    We are just assuming here that the sweet smell cpacpa reported is fungal related. I would have someone qualified take a look into the airstream portions of the system and look for the cause. It may be fungal or it may be something entirely unrelated.

  6. #6

    sweet smell in ducts

    I, too, have that sweet smell from ductwork. The smell runs throughout my entire home. Air conditioner or furnace heat, it does not matter, both enhance this smell. Please help.

  7. #7
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    633
    Quote Originally Posted by rosann View Post
    I, too, have that sweet smell from ductwork. The smell runs throughout my entire home. Air conditioner or furnace heat, it does not matter, both enhance this smell. Please help.
    It could be dirty sock syndrom. Which is hard to get rid of. Try searching dirty sock and see if anything sounds (smells) familiar.

    dogboy

  8. #8

    sweet smell in ductwork

    dogboy.....besides the dirty sock syndrom, what do you know about a sweet smell coming out of ductwork into every room........which means this is originating in the ductwork? My furnace is fairly new, so do not think it is the furnace. However, I will check on the sock syndrom. thank you.. Rosann

  9. #9
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    633
    I was assuming you had a heat pump. Alot of people call their heat a furnace when in fact it is a heat pump. If it is a heat pump it could still be dirty sock syndrome as the heat pump goes into defrost anytime below 45* (a/c mode). If you have a humidifier you could still possibly have dirty sock syn. Best to have a prof. come out and check it.

    dogboy

  10. #10
    Join Date
    Mar 2005
    Posts
    997
    It will not be SSS being it is a sweat smell. I have smelled insulation that can give off the smell. I'd check the insulation in the ahu for the smell

  11. #11
    Join Date
    Jul 2008
    Location
    Southeast michigan
    Posts
    93
    depending on where your system is located and whats all in the same room ....sometimes vent gas can seem to smell sweet...id call your local service company

  12. #12
    Vaporized antifreeze has a distinct sweet smell. i was working on several different choices and got stuck. try to google the problem.

  13. #13
    cpacpa
    Do you have an Electronic Air Cleaner or some other air cleaning device that generates ozone? Ozone has a distinct sweet smell for some people.

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