8 Replies Latest reply: Oct 18, 2013 10:30 AM by Mod-Sarah RSS

Cool to Dry still not working

 Grakoos Explorer

I'm still having this problem after the 3.51 update. Humidity is not a problem when every day is hot & sunny and the compressor is running a lot to keep the temp at 80. But when there are a few rainy days - or a week of rainy days - the humidity creeps up.


I've posted about this before, and tech support locked the thread as "answered". But the problem is still occurring.


Right now I've been away for two weeks. Away mode has been set that whole time, and temp is set to 80. The Nest does a good job of keeping the temp from going above 80. And the humidity inside is ok as long as every day is hot, sunny and 95 outside. But if its raining and 80 outside, the inside humidity gets too high. Right now its 60%, temp at 81 and Nest has yet to kick in Cool to Dry mode.


I have an independent environment monitor in my condo and I can see each and every time the compressor kicks in. Its only running maybe 30 minutes a day due to the recent rainy weather in Florida. I could lower the Away temp to 79 or lower, but I shouldn't have to play with it.



  • Re: Cool to Dry still not working
    Nest Employee

    Hi Grakoos


    Nests Cool to Dry feature won't run the AC while you're home, unless the humidity level is above 75%. While you're gone, it'll run it if the humidity level goes above 55%.


    It is also restricted by the temperature, as it will only cool to 75 when in Cool to Dry mode, or 5 degrees below the target temperature, whichever is higher. This is to prevent it from eating up too much energy trying to reduce humidity.


    From what you've described, 60% humidity is not high enough to trigger Cool to Dry, and most AC systems aren't efficient enough to reduce the humidity level that low without constantly running for hours at a time.


    Check out this article:

    Nest |What is Cool to Dry?



    -Calvin C.

    • Re: Cool to Dry still not working
       Grakoos Explorer

      My situation meets all the parameters for Cool To Dry to activate, and the last time Nest tech support looked at it, they agreed with me.


      - I have been away > 2 weeks with AWAY mode manually activated for over two weeks

      - AWAY temp set to 80

      - humidity has been above 55% for the past week, averaging about 60%

      - temperature stays at 80 +/- 1 degree

      - Cool To Dry doesn't activate, compressor only comes on when temp gets to 81


      From past experience, if I lower the AWAY temp to 78, the humidity will drop below 50%. But I shouldn't have to be continually playing with it. Then I'm manually controlling the humidity and probably using even more electricity.

    • Re: Cool to Dry still not working
       Grakoos Explorer


      Graph from my environment sensor, located about 15' from the Nest. It's humidity readings are consistently about 6 - 7% lower than what the Nest reads. There were several days of rain, which caused the humidity "bump" in the past 7 days.

      • Re: Cool to Dry still not working
         tferoli New Nester

        I am having the same issue:


        - Nest in Auto Away over 72hours (currently a week in auto away)

        - Away temp set to 80 deg F

        - Humidity currently at 67 % and climbing

        - Temperature currently at 79 deg F

        - Did a reset

        - Nest does not attempt "cool to dry" at all.


        I called and spoke with support and was asked to turn the fan off of "everyday" mode, so that it is back to 'auto'.  This did not seem to help at all in any immediate way.  I will be calling support tomorrow to continue resolution...

        • Re: Cool to Dry still not working
          Nest Employee

          Hey tferoli,


          I apologize for the delayed response.


          It looks like you've been in contact with senior support. Make sure to stay in contact with the agent you're working. If Nest doesn't activate Cool to Dry after following the steps given to you, we'll want you to call back in.


          Please call us at 855-4MY-NEST (855-469-6378). Our support team is available 7 days a week from 5 am - 9 pm pacific.


          Thanks -


          Rhiana B.

  • Re: Cool to Dry still not working
     Grakoos Explorer

    Since Cool to Dry never comes on even when the humidity is 60% and climbing, I've temporarily reduced my Away temperature to 79F. That seems to do the trick at keeping humidity down, but I'm sure its going to use more energy. Maybe the next firmware will finally fix this broken feature. Otherwise, I'm very happy with my Nest.

  • Re: Cool to Dry still not working
     Grakoos Explorer

    October update: Although Cool-to-Dry doesn't seem to work at all in Cool Mode, it does seem to work in Heat/Cool mode.


    After fighting this for months, I saw a comment by another Nest owner that there was a known bug (or undocumented feature) that Cool-To-Dry only worked in Heat/Cool mode. It was one of the few things I had not tried, and now 3 weeks later - without having to adjust the Away temperature - my humidity is 45% instead of 70%!


    I thought this might be helpful to other Nest owners, especially in Florida.

    • Re: Cool to Dry still not working
       Mod-Sarah Nest Employee

      Hi Grakoos,


      One thing to note in this is that when you are Away, the humidity must be GREATER than 60% in order for Cool to Dry to activate.  If it is at 60% or below, as read by the Nest Learning Thermostat, it will not activate.


      Obviously, if you adjust the temperature cooler in your house, then the AC will run more and it is the fact that the air is getting chilled that is removing the humidity from the air.  So the more you run it, the lower the relative humidity.  That is what you saw when you reduced it to 79 degrees.


      Also, I am not sure if the Heat - Cool mode is what has fixed it.  Temperatures have cooled down and humidity has dropped as we have moved into October.  Cool to Dry will only lower the humidity to 55%, no lower, so the fact that you are getting down to 45% means the weather has more to do with it and the regular cooling of your house than Cool to Dry.


      Please consider calling us at 855-469-6378. Our support team is available 7 days a week from 5am - 9pm pacific.


      We can help you go through this and just make sure.




      Sarah G