The mini-split route idea is a great solution, but I am wondering if you have an unvented or poorly insulated attic that is a contributing factor to your problem. If your attic space isn't setup properly and you throw a mini-split at the problem, it is sort of like pumping water out of a boat without fixing the leak that is flooding the boat. Even something as "simple" as a powered attic vent could help in HVAC performance and operating costs. If the hot air can't vent or your insulation is inadequate, it just stacks down and heats the top floor.
The other thing I would be looking at is if the HVAC run up to the second floor is done properly or if the dampers are not right. A house that size really shouldn't have much trouble if everything is balanced right.
Closing vents on the first floor and leaving the second floor open will increase the wear on the fan and may decrease efficiency if not enough air can be moved through the open vents. Knowing how bad an idea that is would require some measurements and math.
Having the nest with a second temp sensor would just force your HVAC to work harder to cool the upstairs. The single sensor nest can be a smart move to reduce costs with the higher degree of control.
Having dampers installed does more or less the same thing as closing vents, but with a higher cost. A zoned system is expensive and kind of silly on a house of that size.
The mini-split route idea is a great solution, but I am wondering if you have an unvented or poorly insulated attic that is a contributing factor to your problem. If your attic space isn't setup properly and you throw a mini-split at the problem, it is sort of like pumping water out of a boat without fixing the leak that is flooding the boat. Even something as "simple" as a powered attic vent could help in HVAC performance and operating costs. If the hot air can't vent or your insulation is inadequate, it just stacks down and heats the top floor.
Unfortunately, I don't live in a free-standing house. It's a townhouse, so it's connected to other units so I don't think that I can make changes to the attic.
The other thing I would be looking at is if the HVAC run up to the second floor is done properly or if the dampers are not right. A house that size really shouldn't have much trouble if everything is balanced right.
I don't seem to have any dampers at all as far as I can tell.
Having the nest with a second temp sensor would just force your HVAC to work harder to cool the upstairs.
Yeah, I get that I would be pushing the HVAC system to simply be on more, but at the very least I could actually set the temperature upstairs instead of having it fluctuate so wildly. Often, I'll set the temp low at night to be more comfortable. It'll be to the point where I'm basically freezing with the sun down. But then in the morning, when the sun rises it's unbearably hot.
The single sensor nest can be a smart move to reduce costs with the higher degree of control.
What do you mean by this?
Having dampers installed does more or less the same thing as closing vents, but with a higher cost. A zoned system is expensive and kind of silly on a house of that size.
So there's no real reason to get dampers installed then?
If you’re in a townhouse, you have an association. The association would be responsible for the common attic and its insulation. Bring this concern to the attention of the board. Could be other people have the same problem and the fix could be attic-related.
LOL good one! Anytime there is damage to common areas, the affected homeowners have to file a claim on their HO6. Its the stupidest thing I've ever encountered. Roof leaked and I had water damage in the ceiling. I had to file a claim for the HOA's $5k deductible.
You would have to get a GC out to inspect the attic and then give you a written recommendation of alterations, which you then would take to your association. Talk with your neighbors and see if they have the same issue, them jumping in on the issue would offer a greater chance of approval. It is possible the association may pay for it if the problem is attic venting, insulation would likely fall on you.
Forcing the system to run more to compensate for the upstairs would drive up your electric bill and may not actually help if the problem is in the attic or balance of the HVAC. You could set the temp lower at night to accomplish the same thing as dual sensors, but you still are just throwing money away that should be better spent on addressing the issue directly.
Having a nest vs non-smart thermostat allows you to set schedules in a smarter way than a regular tstat.
Having dampers allows you to balance the system so the downstairs gets less air than the upstairs, instead of you having to go around closing vents and the downstairs would be cooled better than just shutting vents and sending most of the air upstairs.