How Air Duct Sealing Works

Air duct sealing works by fixing the leaks in your ductwork to improve airflow and efficiency. This can be done manually using mastic sealant and metal foil tape or with an aerosol sealant sprayed inside the ducts. Professionals often perform a leakage test to ensure the job is done right. 

In fact, homeowners lose 20-30% of their conditioned air through leaky ducts. This leads to higher energy bills, uncomfortable rooms, and poor air quality. Sealing your ducts is a simple way to make your home more efficient and comfortable.

Key Takeaways:

• Sealing your ducts improves your home’s energy efficiency, comfort, and indoor air quality.
• Leaky ducts can result in 20-30% of conditioned air being lost, leading to increased energy bills.
• Duct sealing can be done using mastic sealant and metal foil tape or aerosol sealant.
• A professional leakage test by Filterbuy HVAC Solutions ensures your ducts are properly sealed for maximum efficiency.

What is air duct sealing, and why does it matter

Air duct sealing is the process of finding and closing gaps, cracks, and holes in your HVAC ductwork to prevent conditioned air from escaping into unconditioned spaces like attics, crawlspaces, or walls.

Common leak points in ductwork

Most air leaks occur at predictable locations throughout your duct system:

• Boots and registers: Where ducts connect to floor, wall, or ceiling vents
• Seams and joints: Connection points between duct sections
• Take-offs: Branch points where smaller ducts connect to main trunk lines
• Plenum connections: Where ducts attach to your furnace or air handler

How leaks affect your home

Ductwork leaks create a cascade of problems that impact both comfort and costs:

Comfort issues: Rooms become harder to heat or cool, creating hot and cold spots throughout your home. Some rooms may never reach the desired temperature, while others become stuffy or drafty.

Higher energy bills: Your HVAC system works overtime to compensate for lost conditioned air, increasing energy consumption by 20-40%.

Poor indoor air quality: Leaky ducts pull in unfiltered air from dusty attics, damp crawlspaces, or garages, introducing pollutants, allergens, and moisture into your living space.

Equipment strain: Your system runs longer cycles to maintain temperature, leading to premature wear and more frequent repairs.

The two main ways sealing is done

Manual sealing (mastic + UL 181 foil tape)

Manual sealing involves physically accessing ductwork and applying sealants by hand. This traditional method works best when ducts are easily reachable and visible.

When to use manual sealing: Choose this method for accessible ductwork in basements, crawlspaces you can navigate, or exposed runs in unfinished areas. It’s also ideal for targeting specific, visible leaks.

Materials and durability: Professional-grade mastic duct sealant acts like a flexible caulk that remains pliable over time. UL 181 metal foil tape provides reinforcement and long-term adhesion. When properly applied to clean, dry surfaces, these seals can last 15-20 years or more.

Never use cloth “duct tape”: Despite its name, cloth duct tape isn’t designed for HVAC applications. Its adhesive fails in temperature extremes, and the backing material can degrade, leaving sticky residue and gaps.

Manual sealing process:

1. Clean surfaces around leak areas to remove dust, debris, and loose material
2. Apply mastic to gaps and cracks, using fiberglass mesh for larger openings
3. Reinforce with UL 181 foil tape over sealed areas for added durability
4. Allow to cure according to the manufacturer’s specifications before system operation

Sealing ductwork from the inside (aerosol method)

Aerosol duct sealing represents a revolutionary approach that seals ducts from the inside without requiring physical access to every leak.

How aerosol sealing works: Technicians temporarily seal all registers and returns, then pressurize the duct system. A specialized machine injects aerosolized particles that travel through the ductwork. These particles naturally collect and bond at leak edges, building up layers until openings are sealed.

When aerosol sealing is ideal: This method excels for inaccessible ductwork hidden in walls, between floors, or in tight crawlspaces. It’s particularly valuable in older homes where accessing all ducts would require extensive demolition.

DIY Aeroseal duct sealing myths: While some homeowners consider DIY aerosol sealing, the process requires specialized equipment costing thousands of dollars, precise pressure controls, and professional training. The testing equipment alone—needed to verify results—typically exceeds DIY budgets.

Get a test-and-seal visit from Filterbuy HVAC Solutions—we’ll measure before/after leakage, seal what’s leaking, and set you up with the right pleated MERV 8/11/13 filters to protect your system.

Does Air Duct Sealing Help?

Air duct sealing helps your home be safer, healthier, and more energy-efficient.

1. Air duct sealing helps with energy efficiency and lower utility bills.

It’s estimated that in the average home, 20-30% of the air in the HVAC system can be lost due to leaks, with many consequences.

When you lose that much air, you’re paying for air that you don’t use. That means higher utility bills in the summer and winter, especially when your HVAC system needs to work harder to make your house comfortable. When you get an air duct seal, you may see lower utility bills.

2. Air duct sealing helps your home to be safer and healthier.

If the outside air is leaking in through poorly sealed ducts, you may be living with outdoor pollution in your home. Also, leaks can allow byproducts of large appliances to leak into the spaces of your home that should be free and clear. You may have a room that’s extra stuffy or smells like mildew because vapor from your dryer is leaking into it, instead of being pushed safely to the outside of the system.

3. Air duct sealing helps your home be more comfortable.

With less air loss from your HVAC system, it becomes easier to control the indoor environment, and therefore creates the perfect temperature for your family no matter the temperature outside.

Why Is It Important to Perform an Air Duct Test for Leakage?

Now that we know how important air duct leakage is, let’s learn how to address the problem. How do you know if you need professional air duct sealing?

You won’t be able to tell visually. Not only is the entirety of your duct system likely inaccessible to you, but the leaks can also be so small that it would be almost impossible to see them with the naked eye.

Leaks can occur from tiny tears in ducts, cracks in old caulking, and even bends or holes made by age, pests, or inefficiencies.

If you’ve never had an air duct seal or it’s been several years, it’s important to perform proper tests for air duct leakage. Another risk factor is home remodeling– your system can take on more dust and debris than usual during a remodel, which can overload it and make it more prone to leaks.

How Do You Detect Air Leaks in Your Home?

The Department of Energy recommends that you hire an expert to give your home a thorough and professional energy assessment that you can rely on. An expert will be able to pinpoint problem areas and make recommendations based on their sensitive equipment.

However, if you’d like to do a check yourself before bringing in a professional, you can try the following basic building pressurization test:

1. Turn off all combustion appliances on a cold, windy day
2. Shut all windows, doors, and fireplace flues
3. Turn on all exhaust fans, such as above the stove, in the bathroom, etc.– basically, any fan that carries air outside
4. Carry a lit incense stick past places vents that should blow air into your house– if the smoke wavers or is sucked toward the vent, that means there is probably a leak nearby

How Do You Seal a Leaky Air Duct?

There are a few different techniques and materials to seal air ducts, depending on the location and severity of the leak.

One sealant is mastic tape, which is good for straightforward, large sealing jobs. Another common sealant is caulk, great for those hard-to-tape places. There is also an air duct sealant that can be sprayed inside the duct to seal from the inside, which will be discussed further below.

It is our strong recommendation that you hire a professional if you want to secure your home with the best air duct sealing. DIY projects can make things worse and be more expensive to correct when professional duct sealers are finally called.

Can You Seal Air Ducts From the Inside?

Sealing air ducts from the inside is possible with a sealant called Aeroseal, which was developed in the Lawrence Berkeley National Laboratory to fill building energy leaks.

This sealant was created due to the difficulty of sealing ducts from the outside, especially in extremely hard-to-access ductwork. It was and remains a major scientific achievement.

The research team had to find a way to make sealant particulates that were light enough to travel down a duct, and heavy enough to land and fill the leaks in the duct. It was a balancing act that they achieved, and then continued to perfect via optimization of the aerosol and the application process.

What Is Air Duct Sealant Used For?

Air duct sealant is used for filling holes in the costly leaks that can occur throughout a duct system.

The application of an aerosolized sealant is a process best left to an air duct sealing service, as it can be complicated.

Each portion of the duct to be sealed must be sealed from the outside and pressurized to ensure that the aerosol doesn’t leak out. Then, the sealant is sprayed into the duct with specialized equipment.

The goal is for the sealant to find every tiny hole in the duct, and settle around it in order to make a seal.

How Long Does Air Duct Sealant Last?

Many factors determine how long an air duct sealant will last. They can include the age of the HVAC system, the climate in which the building is located, the efficiency of the appliances that rely on the HVAC system, how often the filters are changed, and how well the rest of the system is maintained.

When in doubt as to whether your sealant is holding, perform a test at home, or ask a local professional air duct sealing service. If you notice any signs that your air ducts aren’t working perfectly, a Filterbuy HVAC Solutions professional will be happy to examine your situation and give you professional, honest advice.

Can You Seal Air Ducts Yourself?

It’s the opinion of Filterbuy HVAC Solutions experts and the US Department of Energy that ductwork is best left to professional duct sealers. While you may be handy with a caulk gun, you will have problems accessing the entirety of your duct system and will lack the knowledge that comes from years of experience.

Choosing to work with a professional has many long-lasting benefits, while DIY air duct sealing can leave you and your home open to many problems.

How Much Does Air Duct Sealing Cost and Is It Worth It?

The cost of your air duct sealing will depend on the size and age of your system, the state of maintenance, the climate in your area, and the amount of time since your last duct cleaning and seal.

If you’re the kind of homeowner who wants their HVAC system and large appliances to be working as perfectly as possible, wants to save money by being more energy-efficient, and wants to maintain the health of the home through the elimination of indoor air pollution, air duct sealing is worth it.

Benefits of Air Duct Sealing Services

The benefits of air duct sealing are many, and the downsides are few.

Benefits include:

• Lower energy bills due to increased efficiency
• Higher indoor air quality
• Increased longevity on HVAC-connected appliances

The only downside will be wishing that you had done it sooner when there was less leakage!

It’s better late than never to take care of air duct sealing and your home. Indoor air quality is one of the important factors to your overall health and the comfort of your home. Air duct sealing is a big part of maintaining indoor air quality.

Ready for Air Duct Sealing?

Filterbuy HVAC Solutions professionals are dedicated to helping you maintain the highest possible indoor air quality through targeted services such as air duct cleaning and dryer vent cleaning. We focus on healthy air in your home to give you the gift of peace of mind.

Filterbuy HVAC Solutions offers thorough, expert, detailed air duct cleaning, to help you know that your ducts are in working order. Professionals have the tools, knowledge, and capabilities to get into the nitty-gritty of your air ducts, and they will be sure to leave your air ducts sparkling clean, which is crucial for your indoor air quality and comfort in your home. In addition, Filterbuy HVAC Solutions also offers a service that you need more often than you think: dryer vent cleaning.

Put simply, Filterbuy HVAC Solutions is dedicated to providing the peace of mind that comes through allowing experts to take care of your home as if it were their own. We’re committed to educating our customers and letting them know when they can handle a problem themselves, and when they should turn to a professional.

While you may find DIY air duct seal articles out there, it is our strong belief that it’s better to place such an important task in the hands of a professional. No matter how handy a person is, they simply don’t have access to the tools, knowledge, and experience that a professional brings to the table. Our Filterbuy air duct cleaning experts are hyper-focused on what they do best, to allow you to relax and do what you do best while enjoying a healthy, happy home.

Frequently Asked Questions

Is HVAC duct sealing worth it for most homes?

Yes, when ducts leak, conditioned air escapes, and unfiltered air sneaks in. Sealing restores designed airflow, improves comfort, and can lower energy waste by 10-30% in many homes.

What’s the best way to seal air ducts—mastic duct sealant, foil tape, or aerosol?

For accessible seams, mastic duct sealant plus UL 181 metal foil tape is the durable standard. For hidden or hard-to-reach runs, an aerosol duct sealant that seals from the inside is often the cleanest solution.

How is duct sealing done, step by step?

Pros test leakage (CFM25), prep surfaces, apply mastic and foil tape—or pressurize the system and inject an aerosol that bonds at leaks—then retest to verify results.

How long does duct sealing typically last?

When applied to clean, dry surfaces (and ducts remain dry), mastic/foil-tape seals are long-lasting. Aerosol seals also hold up well; longevity depends on system condition and moisture control.

Can I seal my own ductwork?

You can seal small, accessible seams with mastic and UL-rated foil tape. DIY Aeroseal duct sealing isn’t practical—internal/aerosol methods require specialized equipment and post-testing.

How do I know if my ductwork isn’t fully sealed?

Signs include uneven room temps, dustier rooms, whistling at joints, or high bills. A duct leakage test (CFM25 at 25 Pa) is the definitive way to measure it.

How much does it cost to seal ductwork—and what about Aeroseal duct sealing cost?

Costs vary by home size, accessibility, and method. Manual sealing is typically priced by time/materials; Aeroseal duct sealing cost reflects setup, equipment, and whole-home coverage. Get a test-based quote after a baseline leakage check.

Which is the best solution to air duct leakage problems?

For exposed runs and minor leaks, manual sealing is ideal. For concealed or extensive leaks, sealing ductwork from the inside with an aerosol method delivers full-system coverage and a before/after report.

Does all ducting need to be sealed?

Any supply/return runs that pass through unconditioned spaces (attic, crawlspace, garage) should be sealed; even short, accessible sections benefit from tightening.

I saw threads about duct sealing on Reddit—Is duct sealing legitimate?

Yes. Mixed forum opinions often stem from poor workmanship or no post-test. Done right—with a pre/post duct blaster test—sealing delivers measurable leakage reductions.

How much does it cost to seal HVAC ductwork overall?

Expect pricing to scale with system size, access, and whether you choose manual sealing or an internal/aerosol approach. Ask for a written before/after CFM25 report with any quote.

Is it safe to seal HVAC duct gaps with silicone?

Silicone isn’t the standard for ducts. Use UL-rated mastic and UL 181 metal foil tape; avoid unapproved sealants inside supply ducts due to adhesion and rating concerns.

What are the benefits of Aeroseal duct sealing?

Whole-home coverage (even hidden runs), minimal demolition, and a data-backed before/after leakage report—great when access is limited or leakage is widespread.