We live in a two story condo with an open stairwell with loft. We cannot get any consistency in house temperatures througout the year. There is one termostat in the first floor hallway. How do we get balance in temperatures?
Does your furnace have a louver or damper that allows you to split the air between the first and second story? If so you can direct more (cool) air to the second floor in the summer. In the winter you’d want to direct more (warm) air to the first floor.
See the attached picture. You can see that the upper floor damper is pointed down (100% open) while the first floor is about 50% open.
If you can not split the air between the first and second floor then you can shut the register dampers on the first floor registers to force more cooler air upstairs. This should help but is not a cure all.
If these fixes don’t work for you its time to call an HVAC contractor.
I would suggest installing thermostatic controlled dampeners and separate thermostats for the up stairs and down.