Ask HN: Dual-zone thermostat setting, should 2nd floor be higher or lower?

[hbarka]

I’m seeing conflicting advise from HVAC professional on this age-old question. I understand that there will be temperature difference between the floors of a house because of thermodynamics, the obvious rule of warmer air rising to the top.

Given a two-story home with a a dual-zone furnace HVAC: For winter setting, one camp says to set the second floor thermostat to two degrees warmer.[1] The other camp of advise says the other way, to set the second floor two degrees cooler.[2] Let’s assume the two-degree variable is the ideal difference , the contradiction here is which floor should be set warmer.

I believe the second floor should be set warmer because intuitively this seems to be the natural equilibrium. Otherwise one zone will be working harder than the other.

[1] http://www.ncwakehvac.com/optimal-temperature-settings-multiple-hvac-home/

[2] https://bardi.com/how-to-effectively-set-your-thermostat-for-a-multi-story-home/

[hbarka]

I’m discovering that smart thermostats do not have a function for dual-zone or multi-zone integration. They simply advise that you install one for each zone (floor) and set your settings as it may. It’s not wrong but it’s really not smart in the sense of multi-zone integrated smart. The software does not communicate with each other to to know what one is doing. I feel like this is a missed opportunity for smart thermostat makers like Wyze, Ecobee, or Nest. I’ve tried all three, in addition to the original dumb Honeywell thermostat which I regret throwing away. Even though these companies advertise smart “learning” thermostats, it only goes so far as learning the schedule of each unit over time and making a prediction for the next time to switch on, independent of what the other thermostat is doing. This space is ripe for a real smart program which factors the entire integrated house ecosystem and incorporates learning for true balancing, economy, efficiency, and comfort.

[toast0 → hbarka]

> I’m discovering that smart thermostats do not have a function for dual-zone or multi-zone integration.

Yeah, they're just not smart. It would be nice if I could configure my thermostats to agree to not all run the heatpumps at any given time, or at least to stagger startup, because my generator is pretty big, but it's not big enough to handle three heat pumps starting at once, and it's not fun to go out and restart it. Sadly, smart doesn't mean smart.

[prirun]

It doesn't make sense to me to optimize for equal load (runtime?) between zones. The point is to make both zones comfortable for humans. If you use both floors, IMO the temp should be set the same in each zone - whatever is most comfortable for you/your family.

In my 2-story house with separate HVAC units & thermostats, I only use the main floor (with MBR), so in winter I set the 2nd floor cooler and in summer I set it higher. I do that because I'm not up there much and don't care about comfort, yet I don't want to turn it off altogether, which would cause the main floor unit to work much harder.

[hbarka → prirun]

Shouldn’t the goal be to optimize for warmth equilibrium and efficiency? In turn it is the most efficient load for the furnace and also for comfort. If I were to optimize warmth for the 1st floor ignoring the 2nd floor, the heat loss towards the 2nd floor will still occur due to physics, and now the 1st floor zone will be working much harder because it’s really warming both floors now. What should the setting be for the 2nd floor in order to make it a blanket minimizing the upward travel of heat from the 1st floor?

[sp332 → hbarka]

I don't know why you want to balance your furnace load between the two zones, but anyway if you're comfortable, you can do it by raising the upstairs temperature. But to optimize for comfort, set both thermostats the same, and let the lower floor do more work. If you're heating the same amount of air to the same average temperature, I don't see why the overall efficiency would be different.

[Finnucane]

I set them the same. The whole point of two zones is that they go on and off independently. Yes, the 2nd floor tends to be a little warmer, so the first floor zone just comes on more.

[bell-cot]

During heating season, or cooling season?

Day (presuming upstairs bedrooms, which are unoccupied) or night (same, occupied)?

Infants & elderly (who may need their bedrooms quite warm), or "healthy younger" folks, who might prefer chillier bedrooms & heavier blankets?

How open are the stairways, for heat to easily rise? Or to be easily blocked with a light curtain, to keep warm air downstairs?

[hbarka → bell-cot]

During winter