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Most homeowners don’t think about sealing the air ducts of their home—but the process is crucial to keeping your house energy efficient. Ducts are what distribute heat and air conditioning to the various rooms of your house, and often these passages have gaps in their connections, allowing the conditioned air to leak out before it reaches the intended room.

A significant amount of energy can be wasted this way. What’s more, if leaky ducts are situated in spaces that get dusty or dirty, those pollutants can get sucked into the system and distributed throughout the house.

To prevent these scenarios from happening, make sure your ducts are sealed, either the old-fashioned way (by applying some tape, mastic, and insulation) or by hiring a professional to blow liquid rubber sealant through the system. Either way, having properly sealed ducts will help you balance the air temperature of your home and improve the air quality.

To Seal Ductwork the Old-Fashioned Way:

  1. Use a continuous strip of foil tape to seal off all longitudinal seams along the straight runs of the duct.
  2. Then use a paintbrush to apply duct mastic to the joints where an elbow connects to a duct.
  3. To apply insulation, measure the circumference of the duct, and use a utility knife to cut foil-faced fiberglass insulation to the proper size (add a couple of inches so the ends can be drawn together easily).
  4. Wrap the insulation around the duct and pinch the seam closed.
  5. Secure the insulation with short strips of foil tape, then apply a long strip of foil tape along the seam.
  6. Repeat until all the ductwork is insulated.
  7. To install pre-formed duct insulation, start by disconnecting an elbow to expose the end of the duct.
  8. Snap a plastic cap onto the duct end to keep the insulation from snagging, then slip the pre-formed piece over the duct.
  9. Gently pull the insulation over the entire length of duct.

To Seal Ductwork from the Inside:

Sealing ductwork from the inside out is a much more complicated process and will likely require hiring a professional. Essentially what they will do is mist the inside of the duct with a liquid rubber sealant.

The contractor will start by removing the grilles from the supply and return registers and plugging them with foam rubber and wide strips of tape. Next, they’ll pressurize the duct system with a blower fan and use a computer to analyze the data to determine the amount of air leaking from the ducts.

Using the blower fan, they’ll mist the interior of the duct system with liquid-rubber sealant, which will plug up all the air-leaking holes, cracks, and seams. Afterwards, the contractor will run another pressurized blower test to verify the improved results.