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  1. #1
    Join Date
    Nov 2007
    Posts
    15

    Honeywell TH8321U question

    Looking at the manual for this thermostat, the lowest it allows me to lock out the auxiliary heat strips is 40 degrees. Is there any way to set this lower, say to around 30, or would that require a different thermostat?

    Thank you.

  2. #2
    Join Date
    Nov 2007
    Location
    Durham,N.C.
    Posts
    117
    Quote Originally Posted by Aaron_FL View Post
    Looking at the manual for this thermostat, the lowest it allows me to lock out the auxiliary heat strips is 40 degrees. Is there any way to set this lower, say to around 30, or would that require a different thermostat?

    Thank you.
    why would you want to lock out heat strip,the compressor is what you need to lock out
    restoring comfort daily

  3. #3
    Join Date
    Nov 2007
    Posts
    15
    Quote Originally Posted by kenshvac View Post
    why would you want to lock out heat strip,the compressor is what you need to lock out
    If the compressor can handle the load by itself down to an outdoor temp of 30 degrees it seems that would be more economical than using the heat strips, due to the greater efficiency of the heat pump vs. the heat strip. Unless my logic is way off base.

  4. #4
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by kenshvac View Post
    why would you want to lock out heat strip,the compressor is what you need to lock out

    i got my heat strips locked out until it hits 15 degrees outside!

    when the stat recovers from setback, it doesn't waste alot of energy trying to recover so fast!



    .

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,048
    Quote Originally Posted by kenshvac View Post
    why would you want to lock out heat strip,the compressor is what you need to lock out
    Don't need to lock out the HP until its COP is less then 1
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    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Nov 2007
    Posts
    15
    I am assuming a VisionPro IAQ stat will do what I want? If I can't do it with my current one I don't know that it would be that much of an advantage to spring for an IAQ stat as it rarely gets down below 40 here anyway.

  7. #7
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    Vision Pro will not do want you want, the IAQ will though.
    Karst means cave. So, I search for caves.

  8. #8
    Join Date
    Nov 2007
    Posts
    15
    There is one other option with my current thermostat, I think. Since it will only lock out aux heat down to 40 degrees this calls for a little creative thinking.

    Looking at the resistance charts for the remote sensor shows a resistance of 22.5k ohms across the sensor at 40 degrees and 17.9k at 50. By paralleling an 87k resistor across the sensor this would give you a resulting resistance of 17.9K at 40 degrees, fooling the stat into thinking it is 50 degrees out, and effectively keeping the aux heat locked out.

    As a result of this the stat would not call for aux heat until it saw a load of 22.5k ohms (40 degrees) across the sensor, or actual air temp of roughly 28 degrees (30k resistance across the sensor at 28 degrees, paralleled with the 87k ohm resistor gives a resistance of 22.3 ohms, pretty darn close to the 22.5 ohms that is the calibrated resistance for 40 degrees)

    Wow, I have been up too long if I am thinking like this, good night.......

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