I have a Tri-level home with two separate furnaces and air conditioning units. One unit controls the lower two levels and another the upstairs level. The lower unit has a thermostat located at the bottom of the stairway leading to the upstairs, and the upstairs had a thermostat at the TOP of those stairs.
Ever since I moved into this home (30+ years ago), I have had uneven heat/cooling of the upstairs rooms. When the heat or cooling would go on, the room temperature would be some 8-10 degrees different from what the thermostat was reading. Eventually the thermostat would be effected by the temperature change and would turn off the heat or AC. The only problem was it ran much longer when it would come on, and the uneven room temperatures.
Recently I read that a thermostat should NOT be installed at the top of a stairs. Obviously heat from the downstairs would tend to rise and impact on the upstairs thermostat when cooling was taking place. The question I have is why the uneven control while heating is taking place? One would think that when the upstairs furnace was on, the stairs would have little or no impact due to the heat rising up?
Finally I decided to do something about this uneven temperature problem. I took a digital thermometer and looked for a location in the same hallway upstairs that was more representative of the true temperature. That is, much warmer than being sensed by the thermostat. After relocating the thermostat some 10 feet away from the stairs the temperature is much more even. I am very happy with the result.
My question is this: I can understand the impact of the stairway on cooling the upstairs, but why did the heating of the upstairs respond poorly as well? I feel I am overlooking something simple, since I know it DOES impact it by the results I achieved.