How to Reduce Resistance in the HVAC Duct System

Straighten out your ducts as much as possible. Bends and curves in the duct system increase the resistance the air has to overcome to reach its destination. Bends in the ducts are often necessary to get the air where it needs to go, but straight ducts increase efficiency.

Seal any duct leaks with mastic and metal tape. Leaks increase resistance in the duct because it creates a split where the air goes in two separate directions at a junction when it's not supposed to. Avoid using duct tape because, ironically, it doesn't work well on ducts and doesn't last as long as metal tape. Apply the mastic with either a clean paintbrush or a caulking tube, depending on the brand of mastic you use.

Add a liner to the duct to smooth out the interior and to help block any leaks from the inside of the duct. Even a small amount of friction inside the duct increases airflow resistance and reduces duct efficiency. Follow installation instructions for your particular liner for best results.