I have a two level 2100sq ft house. The problem I have is the upper floor is usually 10 degrees warmer then the lower level. When it is 95 outside, if I have the stat set to 73, it will be at least 85 upstairs. If I want it to be 75 on the upper floor on a warm night, I have to crank the AC down to 65.

All of the vents are currently 100% open. Is it normal to expect a 10 degree difference between the upper and lower levels? Does the house just need to be balanced, or, does it sound like there might be some other problem?

I have been thinking of zoning, but, want to make sure there is not something else going on first.