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  1. #1
    Join Date
    Feb 2001
    Posts
    447

    Question residual cooling fan time setting

    What is an appropriate residual cooling fan time setting for thermostats in homes in the humid deep south? 0 seconds seems appropriate to me.

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,000
    Could you explain this so a Pro could understand?
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  3. #3
    Join Date
    Feb 2001
    Posts
    447
    As defined by Braeburn, this refers to the time that elapses between when the compressor shuts off and when the air handler shuts off, in heat pump cooling mode.

  4. #4
    Join Date
    Feb 2001
    Posts
    447

    Question

    I realize it's not cooling season, but I can't believe no one has an opinion on this.

  5. #5
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    That should be built into your air handler if you have a realatively modern system.

  6. #6
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by charles2 View Post
    I realize it's not cooling season, but I can't believe no one has an opinion on this.
    Use a short time delay 30/60/90 second to let coil temp raise.

    Do not run continuious fan.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Running the fan after the compressor is off,adds some humidity back to the air.
    How much depends on how well the coil and it's drain pan,drain the water away.Some system have an option to turn off the fan for X seconds/minutes,to allow drainage,then back on.

  8. #8
    Join Date
    Feb 2001
    Posts
    447
    Quote Originally Posted by hvaclover View Post
    That should be built into your air handler if you have a realatively modern system.
    Air handler is a Ruud UBHC-17J11NFD, modern enough? What settings does it have?

    Quote Originally Posted by dash View Post
    Running the fan after the compressor is off,adds some humidity back to the air.
    How much depends on how well the coil and it's drain pan,drain the water away.Some system have an option to turn off the fan for X seconds/minutes,to allow drainage,then back on.
    Precisely. Since it's already too humid in the deep south, would you not want to add zero humidity back to the air? Or is it more important to gain the residual cooling effect? The coil is a Ruud RCBA-3765G.

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    For homes in humid climates with average construction and attic mounted, marginally to zero sealed ductwork, a post cooling call blower off-delay is counterproductive to dehumidifying efforts. In addition to blowing moisture off the coil, as already mentioned, attic mounted ductwork in summer will heat up rapidly after the compressor stops. Air moving through the ducts will be warmed above the return air conditions. Additionally, any air leakage from the ducts into the attic will create a negative pressure in the house, augmenting infiltration of humid air from outdoors.

    IMO, every furnace/air handler made should include the option to completely disable a blower off-delay. Many of the programmable stats have this option, but then that is defeated by a furnace/air handler that does not.

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