This is a bit lengthy but bear with me.

We bought a two level home with a finished basement. All 3 levels are zoned.

The upper level has a hall that runs the length of the house. Six rooms (four bedrooms, a laundry room and a bathroom) come off that hallway. That hall has banisters and is partly open to the level below. THIS ENTIRE UPPER LEVEL HAS ONLY THREE COLD AIR RETURNS. One in the master bedroom, one in another bedroom and one at the end of the hallway. I think that's strange!

In the summer, the heat elevates and this upper level gets HOT. Really HOT!The air conditioner can not cool it down. I believe the main problem is a lack of returns that would remove the hot air from this upper level.

And now my question.

The two bedrooms that do have cold air returns make use of the wall shared by the hallway. Could I cut into the wall in the hallway to add a register that would be on the opposite side of the register in the bedroom? Therefore, a run would have a bedroom and a hallway return. Thus, three returns would become five. Would this move more air out of the hallway and thus the upper level? Should I make these oversized registers to pull more air?

Thank you for any help.

Before I would start cutting for returns, make sure you have plenty of attic insulation, R-30 and attic ventilation. If an attic gets really hot, radiant heat will not be carried away by airflow.

Blown in isulation (plenty) and ridge vents.

Only thing to remember regarding adding vents is that when you reach the supply volume, you cannot remove any more air, regardless of the number of vents. You should have a Test and Balance done to see what is the actual supply CFM and the return CFM. You may have a restricted airflow, dirty filters etc. Perhaps the motor speed could be increased for the air handler. Doors of rooms without returns should not be closed or have at least a 1-2"gap under the door. I would hate to see you do a lot of work without improving the temp.