Three story townhouse, brand new 90+ gas Ruud HVAC system, clean filter. T-stat on middle floor. Middle floor is always warm, upstairs is always several degrees colder. The colder it is outside, the larger the differential between the T-stat setting and the measured temp on the top floor. Last night I set T-stat to 73, woke up to a 67F room that felt even colder than that. Downstairs floor was toasty warm.
Temp measured at the registers on the middle floor is 120F. Temp measured on registers on top floor is 110F, with far less airflow than the downstairs floors.
House was built in 1985, ducts have no internal dampers that I can find. I've closed off most of the bottom floor registers to try to get the furnace to run longer and push more air upstairs, this helps a little.
In the summer, the upstairs gets very hot, and almost no airflow can be felt from the registers. I figured this was because heat rises, but now I'm seeing the opposite problem.....
Installation is just months old and the equipment itself appears to be ok. Furnace is a 75k RGRM Ruud model. I have no idea how the old equipment performed in this house, since I got a new system installed immediately after I moved in.