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So, I'm wondering if there's a way that I can program my Nest thermostats to help moderate temperature disparities between my first and second floors. Here's the situation:

  • I have forced air from a single furnace, with two zones: One for upstairs and one for downstairs.
  • Because the foundation is slab-on-grade, the air registers are in the ceiling for both floors.
  • The lower level has 9' ceilings and the upper level has 8' ceilings.

When heating the home, if I just set the temperatures as desired, the result is invariably that the downstairs zone runs longer than the upstairs zone, and as heat rises from downstairs to upstairs, I get extreme temperature variation between floors, often 6-10 degrees difference.

I can mitigate these temperature variations by a) turning on the ceiling fan downstairs in the reverse direction, and b) setting the thermostats to always run the fan. Doing this, I can often bring the two floors to within 2-3 degrees temperature difference. But here's the problem:

  • It doesn't make sense to run the furnace when the upstairs is too hot, and the downstairs is too cold, if running the fan on both zones helps to decrease the temperature upstairs and decrease the temperature downstairs.
  • It also doesn't make sense to run the upstairs fan while the downstairs is heating most of the time, since the general goal seems to be to keep heat from being transferred from downstairs to upstairs-- I'm assuming running the fan upstairs while the furnace is on is the same is running the furnace upstairs.
  • I'm hoping that resolving the two issues above would help further prevent the upstairs from getting too warm.

I think something like the following conditional programming could be really helpful:

  • If the downstairs is in heating mode and the upstairs is within 3 degrees of the desired temperature, don't heat the upstairs. In this case the fan should be running in the whole house, but only when the downstairs is not heating.
  • If the downstairs is in heating mode and the upstairs is cooler than 3 degrees of the desired temperature, run the heat in both zones until the upstairs is within 3 degrees of the desired temperature.
  • If the upstairs is warmer than the desired temperature and the downstairs is cooler than the desired temperature, and there is a temperature difference greater than 2 degrees, run the fans in both zones and don't run the furnace in any zone until the temperatures are within 2 degrees.

I'm not sure if something like this can be done with the Nest thermostats, or if it makes sense to try what I'm suggesting, but I'm open to ideas that any of you might suggest.

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