Question

I would like more control over my home's HVAC. I live in a two-story home located in MO. The home has a separate AC/heater for the second floor and works well. The main floor and basement have a heat pump which also works well. The home is 6-7 years old. The current thermostat is a generic contractor-grade Emerson. The temperature difference between the basement and main floor is noticeable. What I have noticed is that we are running the AC to cool off the main floor when it is already plenty cool in the basement. I would like the ability to just run the fan to mix air from the two floors before turning on the AC as I feel that just mixing the air would often be sufficient. Is it possible to use external temperature sensors and a smart thermostat to turn on the fan instead of the AC. Then if that is not enough to cool the main floor, then to engage the AC if needed? If so can you all make some recommendations on sensors and smart thermostats? I'm running Hubitat with only a few sensors. I don't want anything cloud-based or cloud-dependent. Curveball: The wife must still be able to operate it from the thermostat. Thanks.  

Answer 1

Is there an actual vent in the basement or is it just the cool air descending down? If theres a vent you could get a smart vent that closes once it gets to a certain temperature. This would then all the AC to only cool the main floor.  

Comments

No, I don't have "smart vents". I have traditional intake and air vents. I'm not a fan of those either - not an option on the table for me.  

Answer 2

Recommendation is to get Rboy thermostat smartapp - you can use any sensor you want to drive your logic

Answer 3

Thermostats wont help your problem, but check out Hibersense. This could really help your flow problem.  

Comments

I agree that just a thermostat won't fix my problem. The Hibersense appears to be in line with what I imagined, but much more data. I don't need ". motion light and much more. " I'm not interested in being a beta tester of a new product that is coming soon.  

Answer 4

I have (had) the same problem. Ended up replacing my furnace with a variable speed, and just leave the fan on 24/7. Heating and cooling season. Winter to move hot air down, summer to move cold air up. And I have a simple manual shut off for all lower level registers in the summer (still gets plenty cold). Been great since. Is leaving the furnace fan on not an option?  

Comments

I'm glad someone else get it. You took an interesting approach. My thermostat does not allow me to control the speed of the fan, but that doesn't mean that the fan could not handle a variable load. That would still mean that I need to shop for a new thermostat, but that does not limit me to a smart thermostat. I'll definitely keep your suggestion in mind. Thanks!  

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@warren5072 yeah I have basically a tri level (full open lower level in back), there was sometimes a 15+ degree difference between the floors. Several furnace contractors I talked to said it's no problem leaving the fan on 24/7, most actually recommended it for normal use. The problem was my old furnace was a beast and very noisy. It needed to be replaced anyway, so the new variable speed I can't even hear while it's running. I know not the most economical solution, but something to keep in mind when it's time for new furnace. I also looked into automated it controllable vent doors, but that wasn't an option for me. The amount I would have needed, and the fact that they always use power, was a turn off for me.  

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@dozier Yeah, the power to run the fan is TINY compared to AC or heat pump. Pennies a day. And on the noise, I get it. I could always hear the fan running in my old house. It drove me crazy. This new house (for me) is quieter. So it's an option if it will handle a variable load. And I think you made the right choice to avoid controllable vent doors. Those things can make your AC freeze up or not cool off your furnace properly. Some folks don't realize the engineering behind the design and proper airflow. I think controllable vents have a purpose, but don't go overboard on those or you won't save any money.  

Answer 5

First, ensure that the ducting connects the second floor and the first floor/basement. I would be surprised it it did and that running the fan alone would equalize the temperature. Thankspically each would be a closed system. Second, you absolutely could do this with any smarthome hub that supported logic based decisions and actions. Homeseer would absolutely do it; it could check the termps from sensors on each floor and make decisions as to what actions should be taken with the controllable thermostats on each unit. It can definitely turn the fan on, set the cooling and heating setpoints, etc.  

Comments

The return air registers on the first floor and basement are on a shared main unit. The duct work is in the basement ceiling which is the floor of the first floor. They run simultaneously and there are no isolation mechanisms. The second floor is isolated. Thank you. I'll look at Homeseer. This is exactly what I want to do is run the fan based on the temps of different rooms. Thank you!  

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@warren5072 Bear in mind that one thing I don't think you can do - and I just asked on the Homeseer forum - is compare the value of one device to that of another device - i. e. IF thermostat1_temp > thermostat2_temp THEN do something. That being said, I do things like check the outdoor temperature and set the thermostats based on that. I like it a little warm, so I will set the thermostats to a specific temperature based on if it's cold out or hot out.  

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@gerdes67 Thanks. I can build that logic into my Hubitat bridge such as if therm1_temp is 5 degrees less than therm2_temp, then engage fan for 15 min. If temp does not move, then engage AC. As long as I can control the fan separately, the logic can be controlled by my Hubitat. At least, that's my goal.  

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@warren5072 That depends on the thermostat. Make sure yours supports that.  

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Geez. It seems that there are dozens of "smart" thermostats on the market and the definition of some "smart" is diluted and a joke. The most common is "control your thermostat while away". Who the heck cares? If you have it programmed or sensor-driven, you don't need to control it remotely. So far, I've only found a few that will integrate with a hub and provide separate fan control. Rant over.  

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Yes, I'm using z-wave. I'll check it out. Thanks!  

Answer 6

Ecobee with remote sensors can do all of this and more with ST integration.  

Answer 7

You could create zones. Depending how handy you are or hire an HVAC. You put a third t-stat in the basement and it calls for cool air only when it needs it. Then won't chill the main floor too. OR you can put in smart stats like ecobee and run a script in webcore. I don't know exactly the code to type but the community is helpful. Something like if it calls for AC run the fan for 30 min and if still calling for cool turn on AC? Or schedule fan run times for 10 min every hour to mix the Temps.  

Comments

I could do either but prefer the smart switch for two reasons. The thermostat would be easier for me and HCAV systems are sized for the amount of air they need to circulate. Bad things can happen when you restrict the amount of air flowing through them.  

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@warren5072 not necessarily, consult a HVAC guy. A lot of people put in zone dampers after the fact. It would be the best situation using that with smart algos

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@warren5072 best of luck in your journey! Let us know what you end up doing

Answer 8

Ecobee suite manager with an ecobee thermostat on Hubitat or smartthings if you have either. It has a circulation mode that will determine when it needs to heat or cool based on temps around your house or if it just needs to circulate air.  

Answer 9

You can use a Sonoff dry contact switch, plus Sonoff temp/humid sensor.