If there are HVAC pros out there, I'd love a little advice. I might get a new HVAC system this year. I like the idea of a variable speed, fully modulating system. However, I live in a small townhouse (slightly over 1K sq. ft.) and I already have issues with airflow upstairs. That, coupled with the inevitability of the stack effect, makes it really hard to cool the upstairs rooms. On summer nights, I set the thermostat to 73 downstairs just so that I can make it 76 upstairs.
While I know variable speed systems offer better humidity control (I live in the South), better efficiency, and are less noisy, I'm worried that a system that normally runs at a lower speed would, given existing airflow issues, utterly fail to cool my upstairs. My understanding is that zoning is not possible in my home given that it's very small and has a central return trunk line for both the upstairs and downstairs. Given that my home is pretty small and isn't that expensive to heat and cool anyway, I'm also not totally convinced that the efficiency gains of a variable speed system will be very significant.
Are these concerns valid, or is the country full of two-story homes with variable speed HVAC systems that perform perfectly well? Maybe I'm overthinking this. I just don't want to pay an extra $2k or whatever for a variable speed system and not realize the benefits and/or end up with an HVAC system that struggles to cool the upstairs even more than my current system struggles to do the same.
If it makes a difference, this would be a heat pump system for AC and heat. I don't have gas lines here, so there's no furnace.