I have a house in CA. Most of the house is downstairs with a master bed/bath upstairs. For various reasons, it is not possible to run ducting between levels. So the upstairs is on a completely separate system.
The problem is the upstairs is always too hot. Even in the dead of winter, the outside high was probably 50 F today, the upstairs AC turns on (thermo set at 77)
Any time anyone heats up the downstair (shower, cooking, furnace) all the heat immediately goes upstairs. Unless someone babysits opening and closing a window upstairs to regulate the temp, the upstairs AC will run. End result is the upstairs AC is costing a lot in electricity.
I hired a HVAC contractor to completely redo the downstairs system (which needed to be redone anyway, and was not done by a HVAC contractor initially). Presumably did a load analysis considering the upstairs. Doesn't think there's any problem since both systems are functioning (functioning meaning if it's >77 upstairs the AC will come on and cool it to 77)
Another person (same company) said the thermo was set too low. I don't think 77 is unreasonable. Any higher I'm afraid will get humid and musty.
I could install a door in the downstairs room the stairs are in. But the registers in that downstairs room would still blow upstairs, there doesn't seem to be a good way to completely isolate the two levels.
I am perfectly willing to hire another HVAC contractor. But I already went through a round of estimates for the new downstairs system and no one really said anything different (just that the downstairs needed to be replaced). I don't want to drag them all back unless I know how to ask what I want.
Thanks so much for your help!