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Sealing Air Leaks Isn’t Just a Wintertime Task — It Also Keeps Conditioned Air In

Leading into the Chicago area’s cold winter, we discussed sealing air leaks so that your cozy home would not suffer heat loss. The same concept holds true for expensively cooled air in the summer: block air leaks and save money on energy bills. Sealing air leaks by using weatherstripping products like spray foam, caulk and mastic sealant is a wise investment year-round. 


Weatherstripping is useful in sealing air leaks because it's designed to be flexible. Weatherstripping products can be applied to doors and windows. If you like choices, you will like the variety of weatherstripping materials:

  • Foam tape
  • Tubular rubber, vinyl or silicone
  • Felt 
  • Metal door sweep
  • V-strip (tension seal)
  • Interlocking metal channel (professional installation only)

The list above is in order of permanence. Foam tape may last a few years. Have a professional install the interlocking metal channel once around all your doors, and you will probably never need to have it done again. The list is also roughly arranged by cost. Invest in weatherstripping materials to keep expensive cool air in and unfiltered, hot air out. 


If it moves, use weatherstripping. If it does not move and leads outdoors, use caulk or expanding spray foam (for bigger gaps). If it does not move and is ductwork, use mastic sealant. Caulk and spray foam can seal up holes where wires, cables and pipes pierce the walls and roof of your home. Caulk serves several purposes:

  • For sealing air leaks
  • For preventing water infiltration
  • For preventing insect or rodent entry

Caulk is available in rigid tubes that work in caulking guns or as flexible squeeze tubes. If you plan to do a serious amount of caulking, buy a solid caulking gun and rigid tubes rather than trying to push it from numerous and pricey squeeze tubes. 
Caulking is a skill best acquired through practice on scrap lumber or corrugated cardboard before attempting it on your home. Most amateurs use too big a bead, and are tempted to tinker with the finished line of caulk. 

A tip for neat application: run painter’s tape or masking tape on either side of your intended target, allow the caulk to set around 20 to 30 minutes, and then peel the tape away at right angles to the bead. You’ll have a clean, professional-looking line. 

Caulk will keep air that has been chilled by your air conditioner inside your Chicago-area home while keeping excess moisture, hot air and unwelcome visitors out. 

Dust Mastic

Your home’s ducts must be sealed at all connections to ensure outside air is not pulled into the treated air moving through the ductwork, or that conditioned air isn't escaping. While most reliable HVAC contractors install ducts correctly, over time the connections can loosen due to changing temperatures (contracting and expanding the metal). Every joint should be sealed with mastic or adhesive-backed metal tape. Avoid standard duct tape – it may have “duct” in the name, but it does not hold up well. 

Seal the joints and connections you can see, but consider bringing in professional help to assess duct connections you cannot see. A professional HVAC contractor can use technology to diagnose and locate unseen duct leaks. If ductwork runs through an attic or unoccupied space, sealing air leaks becomes even more important. An attic’s air may be much warmer than the treated, occupied space below, and the air quality in the attic is much lower than the air you should be breathing inside. A leaky duct in an attic can pull dust, insulation fibers, and hot, humid air into the cool airflow. 


Weatherstripping is nearly interchangeable, and can be mixed in a single application. For example, if you are weatherstripping your front door, a door sweep attached to the bottom of the door helps keep warm air out and cool air in. Around the other three edges you may find it convenient to apply tubular rubber or vinyl. And don’t forget the threshold itself; check that the metal sill plate is well-seated, and – if it has a protruding rubber or plastic gasket – that it's in good shape. 

Walk around the inside of your home to find air leaks. Light a stick of incense and slowly move it around closed doors and windows. If a draft exists in either direction – cool air escaping or warm air entering – the smoke from the incense stick will waft in the direction of the airflow. That tells you where to begin sealing air leaks. 

Weatherstripping with caulk, spray foam and mastic can improve indoor air quality and lower your energy bills. For more guidance on sealing air leaks in your Chicago area home, please contact us at

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