Addressing some comments:

- it's actually a five story townhome, but I left out the top two floors because they don't have these temperature problems, and they're a different system.

- the detectors are not also CO detectors. We had to get some of those and place them around the house as well.

- there are no closed doors anywhere in the house but closets. In fact, there isn't a single door between any two floors in the entire home. There should be a great amount of air flow.

- she recently had a complete audit and cleaning of the entire system. They didn't see anything wrong

- I don't think I'll tamper with the detectors

The reason I asked about closing vents is because while I figured it's okay to close a vent or two (maybe you're sitting near one and don't want it blowing on you), I wasn't sure if it was okay to close entire floors off. The last HVAC guy that came out to her home opened all the vents that I had closed. In the winter I closed the vents on the top two floors of the 3-story system, because no heat was coming to the bottom floor before the top one got warm enough for the thermostat. But this guy didn't like that.