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  1. #1
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    thermostat deadband vs temperature differential

    I see conflicting definitions for "thermostat deadband"; some use the term interchangeably with temp. differential; some say it is related to switching between heating and cooling cycles.

    AFAIK, if the tstat set point is 77F and I program a 3F temp diff, the compressor comes on at 80F and turns off at 77F, for the cooling cycle, right?

    How would a 3F stat deadband work? TIA.

  2. #2
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    A deadband is an area where the heating/cooling never operate. So, 3 degrees would be 1.5 from the setpoint in either direction.

  3. #3
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    Dead ban. The temp range where the HVAC system will neither heat or cool.

    EG: Heat 75, Cool 78. Unit won't heat if temp above 75, nor will it cool if temp is below 78.
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  4. #4
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    It is possible that the meaning of dead band has changed through the years as digital technology has gotten more sophisticated but the dead band was really the temperature swing allowed before the system will come back on. If you have a dead band of 2 degrees then if the thermostat is set to 75 it will cool until it gets to 75 & shut off but will not come back on until it gets to 77. In heating if you set it at 70 then the system will shut off when the temp reaches 70 & will not come back on until the temp reaches 68. Dead band sometimes gets confused with the forced minimum difference setting between heat & cool in auto mode. A 4 degree forced minimum difference setting would mean if you set the cool to 73 then the t-stat would not allow you to set the heat any warmer than 69 in auto mode, which is totally different than the dead band setting.
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  5. #5
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    My stat can be programmed from 1F up to 4F of "temperature differential" and, separately, from 2F to 9F of "auto changeover mode deadband", and I thought I understood both concepts but I am not so sure now.

    Quote Originally Posted by HVAC_Marc View Post
    A deadband is an area where the heating/cooling never operate. So, 3 degrees would be 1.5 from the setpoint in either direction.
    So, deadband is a setting only when configuring the stat for "auto changeover mode" (from heating to cooling)?

    Quote Originally Posted by beenthere View Post
    Dead ban. The temp range where the HVAC system will neither heat or cool.

    EG: Heat 75, Cool 78. Unit won't heat if temp above 75, nor will it cool if temp is below 78.
    sounds similar to the previous answer, but not quite. Are you referring to manual changeover where you set different heat and cool setpoints, or auto changeover where (I presume) you program a single setpoint and a deadband value around the setpoint?

    Quote Originally Posted by garyed View Post
    If you have a dead band of 2 degrees then if the thermostat is set to 75 it will cool until it gets to 75 & shut off but will not come back on until it gets to 77. In heating if you set it at 70 then the system will shut off when the temp reaches 70 & will not come back on until the temp reaches 68.
    This sounds more like temperature differential to me ... at least that's what my stat manual "implies" but doesn't really clearly explain ...

    Quote Originally Posted by garyed View Post
    Dead band sometimes gets confused with the forced minimum difference setting between heat & cool in auto mode. A 4 degree forced minimum difference setting would mean if you set the cool to 73 then the t-stat would not allow you to set the heat any warmer than 69 in auto mode, which is totally different than the dead band setting.
    Yes, this is one of the definitions I read somewhere but now it doesn't sound right.
    .

  6. #6
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    Quote Originally Posted by paul.keenan View Post



    So, deadband is a setting only when configuring the stat for "auto changeover mode" (from heating to cooling)?

    Yep.



    Are you referring to manual changeover where you set different heat and cool setpoints, or auto changeover where (I presume) you program a single setpoint and a deadband value around the setpoint?

    Manual change over doesn't have a dead band.

    Auto change over has a dead band. And it is the area of temp the thermostat will not call for heating or cooling. Whether it be 2 or 10 degrees, that is the dead band.
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  7. #7
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    Quote Originally Posted by paul.keenan View Post

    So, deadband is a setting only when configuring the stat for "auto changeover mode" (from heating to cooling)?
    yes

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    Deadband has nothing to do with auto or manual change over. Deadband is really the play in the temperature between coming on & off. On older t-stats you could set it in single degree increments but most newer ones I assume are in tenths of degrees because they are factory set at 0 & not changeable.
    Here's a clip from Honeywell if you look at the auto changeover differential setting.
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  9. #9
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    Maybe not to Honeywell. Have you checked other brands.
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  10. #10
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    I've mainly used Honeywell which is where I first heard the term deadband, so I've always thought of it the way they described it. I don't know who originally coined the word "deadbeand" but as I said earlier it's meaning might have changed through the years. I guess it really depends on what different manufacturers refer to as deadband so if Honeywell views it different than any other brand then the meaning would change with the manufacturer. So to answer the OP's question correctly we would have to know the brand & model T-stat.
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  12. #11
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    Quote Originally Posted by garyed View Post
    So to answer the OP's question correctly we would have to know the brand & model T-stat.
    AprilAire 8600. There is a menu item for "auto changeover mode deadband" from 2F to 9F and no further explanations. So apparently deadband only applies to auto changeover (from heating to cooling and vice versa) for this stat but maybe it is used or implemented differently for different features/functions on other devices.

    So for now I guess I will keep using manual changeover until I can figure out how to properly configure deadband for auto changeover and how it interacts with other functions such as temperature differential, progressive recovery, and proportional factor period (P/I) ...

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    I just looked at that stat & what they consider deadband is totally different than what Honeywell considers it to be. They're using deadband as the minimum number of degree difference you can set between both modes heat or cool. If the deadband is set to 3 then that should mean if you set the cool to 75* then it will only allow you to set the heat to 72* or lower in auto mode. It is only used to make sure you don't set heat & cool too close together in auto mode to possibly cause the system to run in both modes unnecessarily.
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  14. #13
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    Quote Originally Posted by paul.keenan View Post
    AprilAire 8600. There is a menu item for "auto changeover mode deadband" from 2F to 9F and no further explanations. So apparently deadband only applies to auto changeover (from heating to cooling and vice versa) for this stat but maybe it is used or implemented differently for different features/functions on other devices.

    So for now I guess I will keep using manual changeover until I can figure out how to properly configure deadband for auto changeover and how it interacts with other functions such as temperature differential, progressive recovery, and proportional factor period (P/I) ...
    It has no effect on anything other than how close you can set the cooling and heating temps.
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