Quick answer
Duct replacement removes old attic ductwork and installs new, correctly sized R-8 insulated ducts, sealed with mastic, with properly sized returns and balanced airflow to each room. In Miami it is often worth doing with a system replacement, when ducts are 20 or more years old, or when rooms have never cooled evenly.
Written by Sylvia Denton, HVAC Guides Editor. Updated 2026-09-22.
Ducts have a lifespan too. Flex duct in a Miami attic degrades over 15 to 25 years as the outer jacket cracks and insulation breaks down. Older duct board crumbles. Joints that were taped instead of sealed separate. And many homes have had rooms added or systems upsized without anyone changing the ductwork that feeds them.
New ducts start with design. We measure the home, calculate the airflow each room needs, and size the trunk, branches and returns to deliver it at the static pressure the air handler is designed for. Undersized returns are one of the most common problems we see; they starve the blower, make the system noisy and reduce efficiency.
Installation matters as much as design. Runs are kept as short and straight as possible, supported so they do not sag, sealed with mastic at every joint, and insulated to current code. When we are done, we balance the airflow so each room gets what it needs.
