Update: A customer's floor vent comment last week changed my whole approach
I was finishing up a job in a 1970s split-level in Springfield, and the homeowner asked if I could check the airflow from a floor vent I'd just cut around. I popped the grate off and saw a solid inch of old carpet fibers and dust packed in the duct below. I told him it was normal buildup, but he said, 'That's been choking my furnace for years, hasn't it?' I realized I've been cutting vents for a decade and never once suggested a quick vacuum before the new carpet goes down. It's such a simple step that helps the whole system. Do you guys usually clean out the ducts you expose, or is that not our job?