I was measuring the difference in temperature between the return air vent and the supply vents in the second floor of this house today. The difference was around nine degrees. I know that’s not the best place to take the measurements, but I’m not a HVAC guy. It was 80 degrees outside. I go in the attic and it jumps out at me that the supply plenum is mounted 7 feet off the bottom of the attic floor. It’s in the top of the attic space where it’s hottest. Is that a really bad choice as to where to run the supply plenum? It just struck me as odd that the temperature differential was so low and then I see the plenum mounted in the hottest part of the attic space?