HVAC Duct Sealing

The duct system is an array of metal duct runs that are intended to supply each run and designated supply register with conditioned air that starts at the furnace. Ideally, the goal is for all of the air that is produced to reach each designated supply register for each room around the home.  Metal is a good conductor of energy and with the leakage that is occurring along the way at each connection, or any areas where two pieces meet, metal on metal, there could be a considerable amount of conditioned air lost as it leaves the plenum and travels through each supply run. By sealing the duct work with metal tape around all seams and connections and then applying mastic duct sealant, it will limit the amount of conditioned air loss within the duct system and actually increase the amount of directional air flow to each individual supply register around the home.  It will also prevent the ambient air around the exposed ducts to infiltrate the duct system, potentially deteriorating the indoor air quality within the home.  The cold air returns for most furnaces are created through the interior wall cavities and framing and are most likely not air tight or sealed cavities.  This lack of sealing and being constructed within wall framing is a design flaw and still allows for ambient air outside the cold air returns to infiltrate the cold air returns and effects and deteriorates the air that you breathe within the home.  It is recommended to seal the cold air returns as well with metal tape and mastic.