Two Ecobees, one house - or two houses under one roof?

I have a two story house with an occupied basement. Two HVAC units - one for the 2nd floor, one for the main floor/basement. Home is in East Tennessee, 2900 sqft.

The problem is that during the winter, the main floor thermostat showed it was in the bottom 10% of the comparable homes in my area. The 2nd floor got an Ecobee a few months ago, but it is showing that it was stellar during the winter compared to other homes. Now that we are starting to see some summer temps, the reverse is happening - the 2nd floor shows it’s suffering and the Main floor is stellar.

There is a stairway connecting the 2nd and main floor, so (as you can guess) with heat rising and cool air sinking, the two units can benefit statistic-wise depending on the time of year. I have set the thermostats up so that they are both set the same so any heat/cooling transfer between the floors is minimized, and that helps - but only a little bit.

The question I have is: Each thermostat is treated as if it is it’s own house. Is there any way to combine the two thermostats so that it looks at the house as a whole instead of two separate houses but under one roof (as Ecobee does)?

Note: The 2nd floor unit was just serviced. We found the coolant level was very low so this undoubtedly lead to unusual behavior (icing up) and resulted in wasted energy use. Ecobee alerted me when it recognized the temp was trending up a few degrees above setpoint even though the unit was on. I recognized the icing behavior using beestat and the tech was very impressed with how it was able to easily show the data. (Good job!) I may (rather, I do) have a small leak somewhere and I’m monitoring this unit, but while the efficiency is expected to increase, the question of combining thermostats still remains.

I have two units as well, one unit is for basement/first floor, and another unit is for second/attic floors. I also have multiple zones for each unit, which complicates matter even more.

I have them setup as a single home with the total square footage excluding basement. We don’t turn on basement heating much in winter.

The reports I get from ecobee are useless to my case because I have multiple zones, and they just sum up runtimes of each thermostat, which doesn’t make sense. I generate my own reports by downloading the data from ecobee and calculate runtimes by finding intersections of times where thermostat where running together, and counting them once.

Anyway, your case is different since you didn’t mention zoning. But one thing I have learned from running two systems in a multi-story house is that you need to make sure they are working together, and not one system compensating for the other. By that I mean that you should check beestat to see how often each system is running during the week or day, and make sure you are setting the temperature setpoints for each thermostat so that the HVAC kicks in equally, or proportional to square footage. As you mentioned, heat rises, and cold air sinks, so you want your first floor temperature setpoint to be same or less than by one degree Fahrenheit compared to the second floor. Typically, you spend most time in first floor during the day, and sleeping in second floor at night. So set the desired temperature for the day on first floor and adjust the second floor to that, and at night set the desired temperature for the second floor and adjust first floor to that.

If you are into automation, you can push this further since ecobee doesn’t support this. In winter, when heating turns on in first floor, you can force second floor heating to turn on as well if it is close to turn on. This way both systems are working together to heat the space instead of first floor system trying to heat first floor but will take longer time because the air is escaping to second floor. And in summer, the reverse would be needed, when second floor cooling is called, you would force first floor cooling to turn on.

Thanks for the reply. And you are right - I have no zones. The house was constructed in 2001 and was not designed with zones in mind.

Our 2nd floor is actually occupied day and night. The master bedroom is on the main floor, and the 2nd floor has two bedrooms, bathroom, and a common area. My daughter and her son live up there. She is doing online school, and uses her bedroom as her school room during the day. (Another daughter occupies our basement and does remote data entry - so all three levels of the house are occupied day and night. Except for dinner time. :slight_smile: ) The 2nd floor area and cooling unit are understandably smaller but get different amounts of sun during the summer. At this point, it does look like the 2nd floor unit is operational more often during the day. The main floor has adequate shade coverage from a porch as well as trees on the southern/western sides with some tree benefit also on the 2nd floor - but morning sun is a problem upstairs.

I still need to get a few months of summer operation to see how the two units work with (or against) each other. I like the idea of offsetting setpoints by 1 degree, I’ll try that. I also need to see if the units are naturally cycling with each other as well, and if they go off cycle if this indicates a problem with the system. It is also a bit of a learning curve for us to figure out how one setting on an Ecobee can affect the other.

At this point, data downloads are happening but I really haven’t started processing data because we have only been operating with an Ecobee upstairs for about 4 months now. Thank you for your feedback - good stuff.