My second story is always warmer in the summer and cooler in the winter than the ground floor. I've had the ducts cleaned and sealed and I've also adjusted the blower motor speed. It occurs to me that most of the ducts to the upstairs go along an outside wall, which might explain a temperature difference between the ground floor and second story. I have no idea how much insulation exists in the walls and I haven't gotten around to actually measuring for a temperature difference from the ducts yet.
I'm wondering if it's possible and practical to remove the end of the supply ducts where they blow up from the floor and put some sort of insulation around them. I think expanding foam would get expensive pretty fast and might cause damage. Any ideas?