I moved into a 30 year old home last December. There is a problem with the HVAC.
I have included a very crude drawing of the floor plan
The problem is that I can't maintain a comfortable temperature in the different rooms of the house. I don't really care about the basement because I seldom use it. The thermostat is located in the great room. It is not in direct sunlight.
Suppose for the sake of discussion that I want the temperature to be 70 degrees.
Suppose that it's cold outside and I set my thermostat to 70 degrees. The great room, kitchen will be about 70 degrees. The bathroom will be warmer. The den will feel about 65. The upstairs will be about 75 or so, and I can break a sweat.
It gets late at night and the bedrooms upstairs are too hot, so I turn the thermostat down to 65 to compensate. The air-conditioner kicks on and the temperature in the bedrooms is now about 70 (which is what I wanted), but it gets very cold downstairs.
When it is warm outside, I still have the problem that it is much warmer upstairs than downstairs.
Why does it seem impossible to maintain a comfortable temperature throughout the house? What do I need to do in order to maintain the same comfortable temperature in all the rooms?