Duct Sealing and why it is important.

Why Duct Sealing is Important

Quick Facts

• A typical duct system can lose around 40% of your cooling and heating energy.
• Just a 20% leak from your ducts causes your HVAC system to work 50% harder to maintain your home’s or office’s temperature.
• Duct leaks can cause problems with mold, leading to possible health and safety issues.
• Leaking ducts lead to higher utility costs and sealing them can save you $300 a year or more.

How duct systems work

A duct system distributes heated or cooled air through a series of tubes to the different rooms of the building. These round or rectangular tubes are typically made of a flexible composite of plastic and wire, fiberglass board, or sheet metal, and they form a branching network throughout homes and office buildings. These duct systems are designed to bring “conditioned” air that’s been cooled or heated by the HVAC (heating, ventilation and air conditioning) equipment, and also return air back to be cooled or heated again.

A typical duct system loses around 25 to 40 percent of the energy output from the HVAC system. Leaks in the ducts are one way that conditioned air can be lost, and this makes the HVAC system work harder. This energy loss increases your utility bills, and it also can make your living or working space less comfortable.

There are two main air-transfer systems in a duct system—the supply and the return. The supply provides conditioned (heated or cooled) air through the registers in each room. That’s the air you feel blowing out from the vents. The return system pulls air back in through the duct system and back to the air handler, to be conditioned and delivered to the supply again.

What happens when a duct system has a leak?

Most ductwork is in spaces that aren’t themselves receiving conditioned air, such as attics and basements, garages, and crawl spaces. This means that the HVAC system is an open system rather than a closed one, and conditioned air can be lost, or non-conditioned air can be brought in.

A leak in the supply ducts can lead to a large loss of cooled or heated air into the non-conditioned space, while a leak in the return ducts pull non-conditioned air into the conditioned space. Both of these kinds of leaks lead to the HVAC system working harder, and a major leak can put a heavier load on the system than it can sustain.

While increased energy costs due to leaks are certainly a problem, that’s not the only issue that leaky ducts can cause. When the system is bringing unconditioned air in, humidity can increase, and that leads to mold and mildew growth. If the outside air is poor-quality, such as from environmental pollution, or hazardous vapors from chemicals that may be stored in the area, that air can be brought into the home, causing health problems.

How do leaks happen?

Homes change as they age, and these changes include materials breaking down, causing damage in various ways. Adhesives dry out and erode, which easily causes leaks. Further, a lot of older cooling and heating systems only have one central return register for the entire home. Individual rooms have their own supply registers, so they can stay comfortable even when doors are closed, but a closed door impedes air from reaching the return register located elsewhere. Conditioned air is still coming in, and so to maintain equilibrium, air escapes through any space available, such as tiny gaps in windows or from leaky ducts into the attic or basement. At the same time, the return duct isn’t pulling in enough conditioned air, so any leaks in the return system pull in outside air from the basement, attic, crawl space, or garage.

Current building codes require both supply and return ducts in each room. Otherwise, air pathways can be created by adding vents into walls or doors. Jumper ducts or transfer vents can connect the vents in different rooms to improve air circulation. It’s also important to make sure there’s no furniture blocking air registers and return vents. Maintaining good circulation helps reduce problems caused by leaky ducts.

Where to check for leaks

If you suspect your duct system has leaks, there are few common places to check. Major leaks are often found at joints where pieces of ductwork are connected. They’re also common near the air handler unit and near vents. In addition to obvious holes or tears, you’ll also want to check for loose joints. Any joint that isn’t properly sealed will leak, even if there isn’t a visible gap. Registers and gaps should be firmly secured. If you have a mechanical closet, it should also be sealed properly, to avoid any negative return-side air leaks, and the return chamber should be free of any debris.

How often to check for leaks

Checking the duct system for leaks is an important maintenance task that can save a lot of money in energy and repair costs. Ductwork should be inspected annually, and if you suspect a significant leak, it’s worth it to have a professional look. Some utility companies and energy raters have diagnostic tools, such as blower-door, duct-blaster, and pressure-pan tests, which can find leaks that are hard for homeowners to find on their own and fix them without inadvertently creating further issues.

The best way to seal duct leaks

If you’ve identified a leak, you’ll want to seal it to improve the operation of your HVAC system. It’s best to work with a professional because they’ll be able to detect and repair leaks most effectively. Supply duct leaks are easier to locate because you can feel the air blowing out or see evidence of it in moving insulation, but it’s important to locate return duct leaks as well, as they draw additional unconditioned air into the system, and this effect is even greater if only the supply system leaks are fixed.

Leaks can be sealed with acrylic-adhesive foil tape or with mastic. Mastic adheres to most surfaces quite well, creating an effective seal that will last. It can be used on its own on cracks that are less than a quarter-inch wide. If foil tape is used properly, it generally has a 20-year guarantee.

Benefits of duct sealing

Ensuring that your duct system is well-sealed will improve your home’s energy efficiency and ensure that your environment will be comfortable and safer from pollutants.

Comfort

When a heating and cooling system isn’t working efficiently, rooms can become too cold in the winter and too hot in the summer. Proper circulation and a system that isn’t leaky will ensure that your entire home remains comfortable.

Air quality

Your air quality is important for your family’s health and safety. A leaky duct system lets in pollutants such as household and garden chemicals, dust, insulation particles, and other allergens. Asthma and allergies can be aggravated when the HVAC system isn’t operating efficiently, so sealing ducts is important to minimize these pollutants in your indoor air.

Safety

If you have gas appliances in your home, such as a water heater, clothes dryer, or furnace, it releases combustion gases, including carbon monoxide, during their normal operation. These are normally vented safely, but if your ductwork is leaky, it can cause backdrafts that pull these gases back into your living space. Sealing ducts will help minimize this risk.

Efficiency

Duct leaks can significantly reduce the efficiency of your heating and cooling system, and that lowered efficiency results in an increase in energy bills. Sealing ducts and improving insulation will increase your home’s energy efficiency, saving you money in the long run. If you’re installing new heating or cooling equipment, making sure your ducts are also well-design and sealed properly can save you money by making it possible to install a smaller system.