I noticed that my new air filters (my size is 20 x 20) are rated at MERV 13 and the register air flow at the 2nd floor seems reduced. I wonder if I should actually go to a "cheapo" filter because my A/C runs continuously during hot days (No. Virginia - June to mid-Sept) at a setting of 76 or lower (resulting in 82 on the 2nd floor).
A less restricted filter would allow more conditioned air to the 2nd floor, is my thinking.
Like many 1-zone A/C 2 story houses, during hot & hotter days (like now) the 2nd floor can be 6-10 degrees warmer than the 1st floor. My house is 1.5 story, "cape cod" type with the 2nd floor basically in the attic. Also, the main 1st floor is in brick which I think helps keep cooler while the 2nd flook is clad by the shingle roof and 1964 insulation and soffit attic venting.
I tried to re-balance by reducing the 1st floor air register flow, thinking more air would be "forced" to the 2nd floor. The 2nd floor is 50% the size of the main 1st floor, and thus, the 4 air registers in the 2nd floor are fighting a lot of heat from being in the attic.