Leaky air ducts can waste up to 30 percent in energy costs and make your home less comfortable. Worse yet, they can pull in dirt and contaminants from your attic and walls. If you’re fighting dust or allergy issues with special furnace filters and air purifiers but don’t seal your ducts, you’re waging a losing battle. You can seal exposed duct joints with mastic, caulk or aluminum tape. (Search for “plug leaky ducts” at familyhandyman.com.) But you can’t seal joints buried in walls and ceilings. Ducts can be sealed from the inside using a process called aerosol duct sealing, but it’s not a DIY project. We contacted Bryan Barnes from Aeroseal LLC to explain how it works and what you can expect in terms of improved energy efficiency and air quality.
Why ducts leak
Rigid sheet metal and fiberglass supply duct joints in older homes were never sealed by the installers. When your blower kicks in and pressurizes the supply runs, up to 40 percent of that air winds up in your wall and joist cavities and attic spaces. Return ducts leak too, but differently. They pull in air from the wall and joist cavities.
How leaks affect room comfort and air quality
HVAC systems are designed to deliver to and remove a certain amount of air from each room. If a room’s supply ducts leak more air than the return duct, the room develops negative air pressure. To make up the deficit, the room sucks in extra air from the supply duct, as well as air from nearby rooms. That causes an air imbalance in other rooms. If the room door is closed, the negative pressure sucks in hot or cold outside air through the gaps around windows, light fixtures, ceiling fans and wall outlets. That air often contains high levels of dust, dirt and allergens, which decrease air quality.
Aerosol duct sealing works from the inside
The installers seal duct openings from the inside by injecting a heated atomized vinyl product under pressure. The material doesn’t coat the interior of the duct. Instead, the vinyl particles attach to leak openings and build up layers until the leak is sealed shut. The sealant can plug holes and gaps up to 5/8 in. across (see Photo 1) and remains rubbery to flex slightly as ducts expand and contract. Larger openings must be sealed using mechanical methods. Most ducts don’t require cleaning before sealing. However, extremely dirty ducts should be cleaned first. Sealed ducts can be cleaned in the future using traditional duct cleaning methods. The application takes four to six hours. The product leaves a mild scent (similar to wood glue) that lasts for about a day. Aeroseal is guaranteed for 10 years, but testing has shown it to last the lifetime of the ductwork.
How much does it cost?
Aerosol duct sealing costs about $1,800 to $2,500 for an average home. You’ll pay the higher cost if your HVAC equipment is in the attic or in a finished basement where access is limited. Based on the projected energy savings, figure a three to five-year payback.
Who should do it?
If you live in a cold climate and have an older home with sheet metal or fiberglass ductwork, you’ll probably save enough on your energy bill to make it worth your while. However, Bryan recommends duct sealing for any home that has comfort issues in rooms on the second floor or rooms far away from the HVAC equipment. In those cases, duct sealing can make the room more comfortable. To find a qualified installer, search online for “aerosol duct sealing.”