Looking for some knowledge on this one. Our new-to-us house is 2 stories, has 2 thermostats (1 downstairs, 1 upstairs), but only 1 a/c unit.

Can the system really control 2 different house levels to 2 different temperatures? What I've noticed is for a/c activity, the top floor thermostat set temp is really the driving force since the top floor is warmer (hot air rises, cool air sinks). So if I set the upstairs thermostat to 70 and the downstairs to 74, the house drives to a temp of 70. The opposite is true for heater activity.

If I want to get a Nest thermostat or something similar, I assume I have to get two (one for upstairs, one for downstairs). But how does that work with setting it to control only 1 shared unit? Is that even possible?

Extra info: I'd also like to have a temp reading in one of the upstairs room (future baby room). Can that work with a Nest system or any other similar system with only 1 a/c unit but 2 thermostats?

Thanks in advance!

Would that setup still allow air flow in the zone that is turned off? Assuming the fan is still on..

So how about needing 2 Nest-style thermostats? Would it work?

Is it a single stage, two stage, or variable unit? I've heard newer variable units can be pretty efficient at zoning….

There is a lot more to a zoned system than just throwing a nest stat on. Nests are, frankly, not really suited for this type of setup except under particular situations where you have a really "dumb" system. If you have a proprietary setup or communicating thermostats, or an EWC board, a nest isn't going to cut it.

Yes, to answer your question, it can and will keep two temperatures on two zones. I had a single 5 ton system at my old house controlling three zones. Regardless of whether you system is single stage, two stage, or variable inverter, you probably will have a bypass damper or a zone controller that will allow the system to work appropriately. Yours is probably set up with a "wild" zone. By that, I mean there is probably a register or more that will run no matter what zone is calling. It's usually a high load room like a living room. The purpose of this zone is to alleviate the pressure of dumping a lot of air into a small zone. Anyway, depending on your setup you may require system specific thermostats. I, personally, would go with a Honeywell over a nest in all cases.

You want 2 ecobee thermostats with remote temp sensors.

Hmm. I will need to look a bit more closely at the system when I get back home tomorrow.

Here are the thermostats I have Honeywell T6 Pro Programmable.

https://www.honeywellhome.com/us/en/products/air/thermostats/programmable-thermostats/t6-pro-programmable-thermostat-up-to-3-heat-2-cool-th6320u2008-u/

Yes, I think the Ecobee with 2 remote sensors seems to be what I'm going for. Or the Honeywell equivalent. One sensor in the downstairs living room and one in the upstairs baby room.

I have the same setup as you. Always a struggle trying to figure out best way to set both thermostats and to what temperatures.

In the winter we can't get the upstairs heat to kick on, because the location of the upstairs thermostat is at the landing at the top of the stairs and we have vaulted ceilings in the living room downstairs. Since heat rises, when the downstairs heat is on.... the hot air rises and makes the upstairs thermostat read a higher temperature. That makes the heat never kick on upstairs and our upstairs bedrooms get really cold.

Also have a struggle in the summer with the AC and setting both thermostats efficiently. Still haven't figured that one out. We've tried setting the upstairs 2 degrees warmer in the summer and also tried setting it 2 degrees colder than the downstairs. Seems setting the upstairs warmer in the summer helps somehow.

Move the upstairs thermostat into a bedroom.

FDXAg said:

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I have the same setup as you. Always a struggle trying to figure out best way to set both thermostats and to what temperatures.

In the winter we can't get the upstairs heat to kick on, because the location of the upstairs thermostat is at the landing at the top of the stairs and we have vaulted ceilings in the living room downstairs. Since heat rises, when the downstairs heat is on.... the hot air rises and makes the upstairs thermostat read a higher temperature. That makes the heat never kick on upstairs and our upstairs bedrooms get really cold.

Also have a struggle in the summer with the AC and setting both thermostats efficiently. Still haven't figured that one out. We've tried setting the upstairs 2 degrees warmer in the summer and also tried setting it 2 degrees colder than the downstairs. Seems setting the upstairs warmer in the summer helps somehow.

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For winter heating, try leaving the fan on "ON" for the upstairs thermostat instead of "AUTO". This will help circulate the air for more consistent temperatures (note: don't do this when cooling, circulating the air when it's humid and not being conditioned can lead to mold issues in the system).

You are correct on the summer mode, you'll want the upstairs a few degrees higher. If it's colder, the cooler air sinks to the first floor and causes the downstairs AC not to turn on, giving you warm downstairs beds and baths.

The old damper system that you have commonly threw air 80-20% to the Call Zone - No Call Zone. Haven't heard of one that completely shut off the other zone. This is not all bad, since humidity levels needs management in both zones.

Would love to hear that a different thermo solves such problems,

Poor HVAC design - perhaps due to economy beyond the "one system" savings - also contributes ala
poor RA locations
open to above/below space are grand & offer no segregation
HVAC runs too long/short & improperly sized

Your future is to replace this One HVAC system with at least Two
and investing in the very best, responsive ones on the market.
It would be a bonus if they could relocate RAs, thermostats and attend to ductwork issues.