One room barely gets airflow on our ducted AC — could the flexible duct be sagging or leaking?

Short answer: yes — sagging, kinked, crushed or disconnected flexible ducts are one of the most common reasons ONE room stays starved even after balancing. Flexible duct is exactly what it sounds like: it sags between supports, kinks around bends, and its joints pull loose — and when it does, airflow to that room collapses and your expensively-cooled air leaks straight into the ceiling void. It's a physical fault, not a setting, so no amount of damper/thermostat tweaking fixes it.

How to tell it from a balancing issue: - Balancing problems shift with damper positions and affect the "share" between rooms. A duct fault is stubborn — that one room is weak regardless of what you do at the dampers, because the air isn't physically getting there. - The giveaway is a room that's far worse than its size/distance should explain, and doesn't respond to balancing.

What's usually found above the ceiling: - Sagged/kinked flex duct — the most common; it droops between supports or kinks at a tight bend, choking flow (like standing on a hose). - A pulled-apart or loose joint — the duct's come off the collar/takeoff, so most of the air blows into the ceiling void before the room. You may notice the ceiling void is oddly cool. - Crushed duct — something resting on it, or it was installed squashed. - Torn/leaky duct or bad insulation — leaks cooled air and gains heat in the hot void.

The fix: someone gets into the ceiling void and re-supports, straightens, re-connects and seals the run (or replaces a damaged section) — and checks it's properly sized. It's access-and-labour work, not a part.

Common mistake: endlessly re-balancing or blaming the AC when the duct to that room is physically compromised. Get an AC team that can inspect and redo the ductwork to check the run to that room. Anyone opened their ceiling and found a duct flopped off entirely?