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  1. #1
    Join Date
    Oct 2012
    Posts
    97

    Setting fan to cycle on auto improved humidity levels - why?

    After reading another thread on here where the poster was advise to set his fan to cycle on auto, I did the same with my Trane XR16 heat pump/Hyperion XL handler combo.

    The fan was set to cycle 20 mins in each hour previously & humidity levels were all over the place & did hit the 40's when the AC was blasting.

    Now it's on auto & runs when the system runs & I've noticed a more comfortable environment & humidity going down to the 45-50% range consistently with no huge spikes when the system is off.

    Why is the reason behind this?

  2. #2
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    2,509
    When the fan is running and the A/C is off, water that has not drained is re-evaporated from the coil and drain pan putting humidity back into the house.

  3. #3
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,037
    "IF" the HVAC ductwork/system is interconnected with the fresh air intake of the home "OR" if at least some of the ductwork is located in an unconditioned space (and it has leakage) ......... the fan running can pull outside/unconditioned air into the home. When the AC is running this isn't normally a problem because it's just seen by the equipment as more load and works to remove the humidity. But, if the AC isn't running this outside air is now brought into the home, along with the outside humidity, and builds up waiting for the next on cycle of the AC unit.

    No matter the reason, you've found a solution to the swings in humidity in your home.

    You can call it a good day and go about life happy with the results, or........... you can "experiment" with what you've found as a solution and figure out why it happened. The first option is what most people do. The second option is what causes the HVAC pro to loose sleep and their hair (right after it turns grey) to fall out. The need to know why something happens and to understand that just when you think you've figured it all out you walk into the house that doesn't play by the rules. That fact is why answers from the pros here sometimes seem to be all over the place. We all basically read the same books and attend the same classes and training, it's the years of real world experience that teaches you that very little is as it seems at first glance.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Oct 2012
    Posts
    97
    Quote Originally Posted by firecontrol View Post
    "IF" the HVAC ductwork/system is interconnected with the fresh air intake of the home "OR" if at least some of the ductwork is located in an unconditioned space (and it has leakage) ......... the fan running can pull outside/unconditioned air into the home. When the AC is running this isn't normally a problem because it's just seen by the equipment as more load and works to remove the humidity. But, if the AC isn't running this outside air is now brought into the home, along with the outside humidity, and builds up waiting for the next on cycle of the AC unit.

    No matter the reason, you've found a solution to the swings in humidity in your home.

    You can call it a good day and go about life happy with the results, or........... you can "experiment" with what you've found as a solution and figure out why it happened. The first option is what most people do. The second option is what causes the HVAC pro to loose sleep and their hair (right after it turns grey) to fall out. The need to know why something happens and to understand that just when you think you've figured it all out you walk into the house that doesn't play by the rules. That fact is why answers from the pros here sometimes seem to be all over the place. We all basically read the same books and attend the same classes and training, it's the years of real world experience that teaches you that very little is as it seems at first glance.

    I'm just a avg. home owner but I like how you put that part above to explain what I've seen as contradicting answers on some topics before here.

    However, even those variations in answers are a great starting point for us avg. joes to start a discussion confidently with professional when we are seeking help in diagnosing our problems in real life.

    Thanks all!

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