Changing Existing A/C Ducts Requires A Mechanical Permit
The Florida Building Code (FBC 2010) and local building departments in South Florida require a mechanical permit to be applied for to install new A/C ducts, even if you are replacing existing ducts. Depending on the the amount of work you may be required to provide drawings by a Florida Architect or Engineer to show the lengths and dimensions of the ducts to assure that proper air distribution and pressure are provided.
Ducts must be properly sized when being replaced to keep the A/C unit working properly and extend the life of the unit. Changes in duct materials, shape and location can alter the performance of the system and require recalculation. Inadequate duct installation and design can lead to damage to the A/C unit, hot/cold zones, sweating ducts (if uninsulated metal duct), whistling air flow and a number of other problems. These issues can cause mold and other unhealthy conditions.