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Seal Exposed Ductwork

Sealing a Duct

Tiny openings in furnace and air conditioning ductwork add up to big energy losses. Permanently plug those leaks to save some green while going green.

Tools & Materials

Use this checklist when you go to the store and purchase your items.


Identifying Leaks

Ductwork is the system in which conditioned air is transported to heat or cool your house.  In an average home, up to 20 percent of that air is lost due to leaks, holes and faulty connections. Look for tiny holes in the tubing, gaps, and branching lines of dust and dirt at duct connections. Most problems are found at the duct joints, duct connections and where ducts meet an air vent or floor register.

Below are signs your ductwork may need attention:

  • High summer and winter utility bills
  • Rooms that are difficult to heat and cool
  • Stuffy rooms
  • Poor air quality, such as excessive dust
  • Ducts are located in the attic, crawlspace or the garage
Ductwork can be hard to access. If you don't feel comfortable making repairs, contact a professional.


Before You Shop for Materials

  • Check to see how much of your ductwork is accessible from the basement, crawlspace, or attic.
  • Check whether ducts are made from sheet metal, fiberglass, flexible tubing, or a combination of these. Tape works especially well on fiberglass and flexible ducts as well as flat metal ducts; liquid duct sealant provides a tight seal around odd-shaped metal joints.
  • Wear eye protection. You’re working beneath dusty ductwork and, in the case of sealant, brushing liquids overhead.


Tape Ductwork


Step 1
Tape Ducts at the Joints

Vacuum ductwork where possible and wipe it clean with soapy water. Check for any loose fittings that can be tightened.



Step 2
Press the Tape in Place With a Putty Knife

Cut a piece of HVAC foil tape long enough to wrap around the duct at each joint.



Step 3

Peel off the paper backing and apply tape centered on the exposed seams in the ductwork. Press the tape in place using a plastic putty knife.

Use a foil-backed, UL-listed, tape with adhesive that resists heat damage and aging. Never use duct tape, it's not long lasting.


Seal Ductwork


Step 1
Seal Your Ducts

Vacuum ductwork where possible and wipe it clean with soapy water. If you find any gaps greater than 1/4 inch, fasten the pieces together again before applying sealant, or cover the gap with flexible mesh tape.



Step 2

Beginning from the top or upper sides, brush sealant onto the ductwork over the joints. Coat the ductwork with bands about 2 inches wide and centered on the seams. Using the brush, work the sealant into the seam. Allow at least one day for the sealant to dry.

Make sure there's plenty of ventilation where you work. You can find solvent-based duct sealants, but a water-based product will give your nose and your house a break.


Benefits

Ensuring your ductwork is properly sealed can:

  • Save money on energy costs
  • Make room temperatures more comfortable
  • Improve indoor air quality
  • Protect the environment by using less energy