I am replacing the flexible ductwork in my attic, which is a mix of ancient 6" and 7" metal ducting. I'm having a hard time finding 7" flexible ductwork for sale locally, but no problem with 6" and 8". For a smaller, fairly open single story ranch house, would it cause excessive airflow issues to use 6" or 8" instead?
This is going to a room with about 160 square feet by the way. An additional, larger room is about 290 square feet that currently has 2x7" ducts to it.