The Beginner’s Guide to Air Duct Sealing: Three Proven Methods

Air duct sealing is usually an afterthought in many home improvement projects, but it can make or break the efficiency of your HVAC systems. Air ducts work by providing convenient pathways for conditioned air from your HVAC equipment to flow into desired rooms.

These pathways are imperfect and have tiny gaps that can leak large amounts of air. 

You can patch up leaking ductworks by using one of the following three methods: 

1. Duct tape (temporary fix)
2. Mastic sealant (quick fix)
3. Aeroseal (expensive but long-lasting)

The Problem with Leaky Air Ducts 

Leakages are a common problem in many homes; it is reported that poorly-sealed duct systems lose about 40 percent of heating or cooling energy.

It takes more time, resources, and effort to cool or heat a house with poorly-sealed air ducts. Leaks undo all the work of your HVAC system, the cooling or heating process starts all over again, and you receive a hefty energy bill at the end of the month.

The human equivalent for this would be breathing through a straw while running. Do this long enough, and your respiratory system will cave in. In the same vein, leaky air ducts can cause a significant burden on your HVAC system.  

To keep this from happening, you have to seal your air ducts.

Additional Benefits of Sealing Air Ducts 

So, beyond improved airflow efficiency, why bother sealing ducts in the first place? Air duct sealing offers a multitude of added benefits.

Preventing the Loss of Cooled or Heated Air 

Some people argue that the air leaking from the duct is still in your house, so the energy isn’t really lost.

But here’s what they’re not considering: If you were to quantify the leakage from typical air ducts, you’ll find that a large majority of homes lose the same amount of air as cutting a basketball-sized hole in the duct. That is a considerable amount of leakage. 

This leaked air usually travels to an area of the house that isn’t needed, such as the basement or attic. However, over time, these small leaks can add up to the amount of air you need to heat or cool your desired room. 

Keeping Dirty Air Out 

Another important fact is that air duct sealing keeps the dirty air and dust out. The return air duct will indiscriminately suck all the air in. Sealing the ductwork will prevent polluted air from entering your air supply. 

Energy Bill Savings

Leaks in the air duct will allow cooled or heated air to escape before it reaches the desired living spaces in the home.

Experts believe that about 20 to 30 percent of the HVAC utility costs result because of duct leaks, which is money that adds up to a significant chunk of change over several months. 

Because the desired room hasn’t achieved the target temperature, the HVAC system works harder and expends more resources to replace the air, resulting in more energy usage and significantly skyrocketing your utility bill. 

The conservation of energy and lower utility bills are two significant benefits of sealing air ducts. 

Better Air Quality

Leaks in the ductwork allow polluted air inside the system, increasing pollutants inside the home, including dust, dirt, and other particles that will diminish air quality. Moreover, your duct system will also require frequent duct cleaning to remove the contaminants. 

If someone in your family has allergies or asthma, sealing the duct system can help reduce their symptoms and improve health.

As mentioned earlier, you can further improve indoor air quality with the help of an air filter. You won’t have to replace the air filter as frequently because there is less work to do. 

Improved HVAC Efficiency 

As mentioned, the loss of energy can cause your HVAC system to work harder to maintain the desired temperature. As a result, the system runs more cycles and operates more frequently, leading to more wear and tear and frequent replacements. 

Good for the Environment

Most cities use energy by burning fossil fuels, which can contribute to climate change, acid rain, and smog. By sealing the ductwork, homes use less energy to cool or heat, which lowers their overall carbon footprint and reduces the amount of air pollution generated.  

There are a variety of air duct sealing techniques you can use to achieve these benefits. Let’s discuss the three best options in more detail.  

The Three Duct Sealing Methods 

You can apply high-quality duct tape (the old-fashioned way), mastic, or Aeroseal sealant for improved results. Each method has its pros and cons, so let’s deep dive into which technique you might use and why. 

You could use a DIY approach or hire a professional. The problem with DIY methods is that you will need to know where the leakage occurs. A much better long-term solution would be to ask a professional to apply liquid rubber sealant through the system. 

Method 1: Good Ol’ Duct Tape (Temporary Fix Only!)

A quick, convenient, and low-mess approach is using air duct sealing tape—its ideal application is even in the material’s name! 

We are not referring to hardware-store duct tape because that won’t do the job. The average hardware store variety of duct tape is poor for duct sealing. It doesn’t even create an air seal and quickly loses adhesion before falling off. 

Ironically, duct tapes can be used in many DIY projects, but ductwork is not one of them. Duct tape is not designed to withstand the extreme temperature fluctuations common with HVAC systems.

We’re not saying it doesn’t work—it does, but you’ll have to manage your expectations.  

When shopping for duct tape, keep a close eye on the type of material used by manufacturers. Butyl duct tape and oriented polypropylene tape (OPP) are good options because they can create a surprisingly good seal around ductwork joints and offer a high level of durability. 

If you want to go down the duct tape route, make sure to buy something even more robust. Aluminum foil tape is a trendier alternative that has shown to be very durable—just not the best. Most hardware stores carry foil tape, but the quality can be hit or miss.  

Pro tip: Tapes tend to stick better to warm surfaces. Ensure the tape is at room temperature, or apply it while the heat is running.  

The Problem With Duct Tape

Duct tape was never really designed to be cover air ducts. Over time, the air will break the adhesives in duct tape, causing it to disintegrate.

It won’t be long before the duct tape falls off, or worse still, get into the air ducts, and the condensation from temperature fluctuations will weaken the tape and cause it to break.

Meanwhile, you’re thinking your ductwork is functioning efficiently while your energy bills are skyrocketing. Not only that, but inefficient duct tape applications will reduce the lifespan of your HVAC system, which is why duct tape should be used as a temporary fix only. 

Method 2: Mastic Duct Sealant 

Note: We are not referring to duct seal putty used to seal tiny areas around electrical wires and conduits.

Mastic duct sealant is a proven method that has been used for air duct sealing. It’s a thick, pasty substance that can be applied to gaps and leaks in the ductwork with a caulking gun and a paintbrush.

A convenient option is to take a gallon bucket full of duct sealant and apply it directly with the help of a paintbrush. Mastic sealants will harden right after application. 

We recommend using a water-based sealant because it is less messy— you do not want to spend hours cleaning up!.

Mastic sealers are very long-lasting when appropriately applied, but you might want to consider them based on whether or not you’ll need access to the area again.

If you plan on opening up the ductwork to clean it up after application, you might be better off using tape instead.  

Pro tip: You may need to combine your mastic sealant with tape if the gap size is bigger than 1/4″. 

There are a few things to keep in mind when applying air duct sealing:

• Always use a water-based duct sealing 
• Wear gloves and a disposable long sleeve shirt 
• Wear a hat and face mask 
• Clean the surface before using the mastic
• Cover all the seams and holes you can find

Method 3: Aeroseal 

The DIY approach to air duct sealing saves you money—but it can be challenging for beginners, especially if you’re trying to get into hard-to-reach areas or when there are hidden leaks behind drywall. For applications like these, we recommend using Aeroseal. 

Aeroseal installation is best carried out by an experienced professional. The technician will pressurize your system by blocking all your vents and registers. 

Pressurization is an essential first step in identifying where the leakage occurs in your ductwork.

Computer technology will then be applied to detect leakages, cracks, and gaps that are not usually visible to the naked eye. The next stage is the application of mastic sealant throughout the ductwork. 

The goal of using computer technology is to apply a precise amount of sealant, ensuring that there is no mess and providing a precise measure of the amount of leaked air. You will be given a nice before and after comparison to indicate the improvement. 

Rooms that weren’t getting enough cool or heated air will now get precisely the amount they require. Aeroseal is effective because it properly seals the ductwork so that no outside air or dust gets into the pipe and is spread around the house.

There will be a significant improvement in air quality noticed almost immediately.  

You can further refine the indoor air quality by getting an air filter, which you won’t have to change very often because there won’t be as much dust or dirt to clean. 

Why Aeroseal is Better

Aeroseal has proven to be both fast and reliable. It can significantly improve cost savings and reduce leakage by almost 90 percent.

As a result, you could save a significant chunk of change every year. Moreover, Aeroseal is made of UL-tested material that doesn’t leave an odor behind. 

Aeroseal is so effective that the US Department of Energy gave it the “Energy 100” award and rated it among its 23 most beneficial technologies. 

The difference between mastic and Aeroseal isn’t really important in the grand scheme of things. Both will do a good job and last a long time.

However, Aeroseal is more effective because it uses a computerized approach to calculate where the leaks are occurring and then patches them up. It is more expensive though. 

Combining Duct Tape with Duct Mastic 

Sometimes the best option is to combine multiple methods for a long-lasting solution. The method below outlines the process of combining duct tape and duct mastic: 

• Take a long strip of duct tape and apply it across longitudinal seams of the air ducts 
• Then, use a paintbrush to generously apply duct mastic to the joints
• Repeat the steps until all of the ductwork has been sealed

Pro tip: Apply insulation around the duct for a better seal. Simply use a utility knife to cut foil-faced fiberglass insulation to the proper size (based on the circumference of the vent).  

Wrapping Up

For many homeowners, air duct sealing isn’t a priority compared to other duct fixes. As a result, many homes have ductwork that is damaged, poorly installed, and leaking all the time.

Through air duct sealing, you will notice improvements that actually solve your problems. However, in some cases, it may be more cost-effective to replace the ductwork entirely if the leakages are too many to fix.