I live in one of the Atlanta suburbs. House is a two-story on full walk-out (daylight) basement. Cooling is done with two zoned AC units (not HP). Approximate heated-SqFt is 2,650 not including the basement, which is 1500/1150 down/up-stairs because of a two-story family and foyer rooms. I have no problems cooling the first floor.
Just me and the wife. Master bedroom & bath are easy to cool. Three other bedrooms (one used as a home theater, one for a guest bedroom, and the last one as my office with two computers).
I got up yesterday with zoned thermostat set to 74ºF. Went and did my yardwork and finished at just before Noon. Came indoors and turned on a computer to check email before taking a shower and set thermostat to 73ºF. Some 45-minutes later I go into the master bedroom to set thermostat to 72ºF (I'm a Yankee) before stepping into shower, and noticed temp was now reading 73ºF. All seemed normal.
Got out of the warm (but not hot) shower and temp was not 74ºF. Okay. Go run some errands and notice two hours pass and thermostat still at 72ºF setting, but temp reading still at 74ºF. I turn off the PC I had left on and went about watching some TV downstairs. I noticed its thermostat was set to 74ºF and the current temp was also 74ºF. Outside it was 84-86ºF. Yesterday's high about 89ºF.
Coming up on 4PM I noticed the upstairs unit is still running non-stp and the reading/setting is still unchanged at 74º/72º. Downstairs its cycling per a normal, expected behavior. Its idea of 74ºF is much cooler than upstairs. Both floors have 9' ceilings and their respective thermostats mounted at about 5'6" height from the floor.
I relax downstairs, do some grilling, snoring, drinking, etc. until 8PM rolls around when its X-Box Live time. My every-Saturday night keeps me downstairs with the guys online playing shoot'em up games. I went to bed at 1AM.
I walts upstairs at 1AM and the thermostat is set where I put it and its still reading 74ºF. I have an alcohol thermometer hanging on the wall in my study and its reading 29ºC, or about 84ºF at 1AM. So, in 11 hours between 2PM yesterday and 1AM today nothing was running upstairs except the fire-alarms and the thermostat itself.
I have two concerns: 74º reading downstairs and upstairs have obvious differences (ones much cooler in reality). When a track-home is outfitted for HVAC what temp do they size the units for? This isn't a heat pump, but a dedicated AC+Furnace setup, and zoned for floors.
I'm not so sure the tubular conduits in the attic, where the second floor zone is located, is keeping the chilled air cool enough by the time it hits the ceiling registers. My attic, which is a moonscape of uneveness covered in blown fiberglass, is very unfriendly--making going up there not desirable.
So, far the HVAC has run non-stop for 3-4 hours and not reached the point of where I set it to. Its warmer upstairs right now with reading/set temps of 72º/71º than downstairs at 74º/75º. I am not sure if the demands an attic fan or not, and also where to install it.
I think a ridge/peak located fan could help remove some of the 120ºF temps in the attic in favor of the 88ºF temps outside. I think its the heated shingles generating the heat in the attic, and then placing a load onto the upstairs area. I'd install the fan myself, but that peak goes up 18 feet.
Any ideas for testing, evaluating, etc. the situation more formally? I'm ready to call an HVAC person, but the idea of spending $3K to upgrade is not a laughing matter.