The simple guide to duct sealing: How much are duct leaks costing you?

Who doesn’t want cleaner air, a more comfortable house, and a more efficient HVAC system? Learn how to get it.

Who doesn’t want cleaner air, a more comfortable house, and a more efficient HVAC system? Learn how to get it.

If you’re like most American homeowners, your recycling bin is littered with ads for various duct repair and duct sealing services.

And, of course, all of them advertise better energy efficiency, cleaner air, and a more comfortable home. 

But is any of that true?

It’s a great question. Since you’re here, you’ve probably got more questions. Among them:

Is duct sealing worth it? How much energy does duct sealing save? And how do you know if you’ve got leaky air ducts anyway?

In this article, you’ll get the answers to all of those questions.

Jump to table of contents

Plus—since we at Sealed are home energy upgrade experts—you’ll also come away with some nerdy duct facts you didn’t ask for, but (we hope!) you’ll be glad to know anyway.

You’ll also learn the most common signs of leaky air ducts and the basics of some DIY fixes. And how to get whole-home weatherization, including duct sealing, at no upfront cost. Tap here to see if your house qualifies.

Basically, by the end of this article you’ll know a lot about ducts. (Don’t worry! The process will be fun. Or at least short.)

Table of contents:

A quick overview of duct leaks

Okay, a quick primer on ducts—and duct leaks.

First, what is a duct system, anyway? In the simplest terms, a duct is any type of channel used to distribute air evenly throughout your home. 

In most homes, ducts look like metal tubes or vents running to and from your HVAC equipment and through walls, ceilings, and crawl spaces. 

If you’re at home and feel like it, you can take a quick look at one now by walking over to the nearest air vent—or register—and shining your cell phone light inside. Exciting!

By the way, here’s your first nerdy duct fact. 

Ducts actually come in two varieties: return ducts and supply ducts. 

Supply ducts deliver conditioned air into the home, while return ducts pull air from inside the home and back into your HVAC system. 

Both are essential for efficient airflow and a comfortable environment. (For our purposes, duct leaks in either return or supply ducts are going to be a problem!)

When your ductwork was first installed (assuming it was properly installed!) it probably worked pretty well (at least for its time) and got most of the air where it needed to go. 

But time is not kind to anything, including ductwork. And if it’s been a while since your ductwork was installed, it’s probably… developed some issues.

Specifically, air leaks—aka duct leaks.


Well, when ducts get old, the materials they’re made of can crack or break—leading to air leaks. 

In addition, the places where ducts are joined (usually called joints) are extremely prone to shifting and separation, which can create a huge air escape problem over time. 

In fact, up to 30% of the conditioned air that’s circulating in your home could be escaping through these kinds of air gaps (1).

Up to 30% of your home’s conditioned air is escaping through duct leaks.

Air Conditioning, Heating, Refrigeration News 

What’s worse, these kinds of leaks don’t just contribute to energy loss, they also allow dust and other irritants into the air you breathe inside your home.

That’s because gaps in your ductwork, allow dust from other areas of the home (think: basement or attic) to get into your airflow—and then catch a free ride throughout the house.

Leaky ducts can also let outside air inside the home, which can bring in allergens, pollen, and other nasties.

In other words, duct leaks are bad news for your wallet—and your health.

So how quickly do ducts develop leaks? There’s no hard and fast rule. But duct problems are inevitable… and the older your house, the more likely it is to have a duct leakage issue. 

(We should also mention here that large old homes with large basements or attics are notorious for efficiency issues like leaky ductwork.)

So what can you do? First, you have to figure out if and where your ducts are leaking. Here’s how to do that.

Back to top

How do you tell if your air ducts are leaking?

In the absence of professional testing, there’s no single way to be sure that your ducts are leaking, but you should look out for a few telltale signs.

Basically, if more than one of the following is happening, leaky ducts might be partially to blame:

  1. You’re experiencing uneven temperatures throughout your house
  2. You’ve got a dust problem
  3. Your ductwork looks bad

1. Uneven temperatures throughout the home.

Here’s a bold but true statement: With 21st-century technology, every house can feel perfectly, evenly comfortable everywhere. 

So if your house feels colder and draftier in some areas and warmer in others, it could mean that conditioned air isn’t reaching those rooms because of—you guessed it!—duct leaks.

By the way, if you’ve got a major temperature issue in your house, here are our guides for troubleshooting an especially stuffy house or an overly humid house.

With 21st-century technology, every house can feel perfectly, evenly comfortable everywhere.

Huge note, though: Uneven temperatures can also be a big indicator that your house isn’t properly sealed and is letting in outside air… or is under-insulated and unable to keep uncomfortable temperatures out. (Honestly, in most older homes, we see a combination of all these issues. You can learn more about that in our guide to weatherizing your home.)

(Related: The complete guide to air sealing)

2. Your home is full of dust

This is a huge indicator of duct issues. 

A little dust is normal, but if you feel like you’re constantly dusting the surfaces in your house, that’s not good—and it can be an indication that unwanted particles and debris are getting sucked into your home’s airways via holes in the ductwork.

3. The ductwork fails the beauty test

Nothing can replace a professional inspection. But, look, if your ductwork doesn’t look good… it probably isn’t good. 

Rust spots, corrosion, signs of moisture or dirt and dust—all of these raise a red flag. And you don’t have to be a professional to see the most obvious duct problems.

Which begs the question: What are the most obvious problems? And how do you verify that your ducts are actually leaking? We’re glad you asked…

Back to top

Two ways to do your own DIY duct leakage test

Ready to dive in and do some testing?

You can do an at-home DIY duct-leak test yourself in two ways:

  1. Visual duct inspection
  2. Smoke test for airflow issues

1. Visual duct inspection

Grab a flashlight and shine it along the length of any ducts you can see. Visually inspect each joint for signs of air leakage or any visible tears or damage.

If you find a leak, make a visible mark—or tab it with a bright sticker—so that all the leaks can be easily traced when it’s time to seal them up (more on this in a minute).

2. Smoke test for duct leaks

First, make sure the air is circulating throughout your duct system—the “fan” setting on your HVAC system is fine. 

Then, grab a smoke pencil (or a stick of incense) and run it slowly along the length of any visible ductwork. 

Any leaks will create disturbances in the way the smoke flows.

The smoke pencil technique is great to find smaller leaks that may not be as visible to the naked eye. 

The big caveat here: However tempting, don’t use matches, candles, or any other smoke source that involves a live flame, as setting the house on fire is generally the most destructive way to discover air leaks.

Okay, safety disclaimers and jokes aside, let’s say you’ve gone over all the ductwork you can access with these methods and noted any leaks. Done and dusted, right?

Not quite. 

While these methods are fantastic for getting a general sense of the condition of the ductwork in your house, they both have a major flaw: No matter how thorough you are when performing a DIY duct leakage test, you’ll always be limited to the ductwork you can see and access. 

And that’s a problem, because a lot of the ductwork in your house probably isn’t accessible.

A DIY duct leakage test is incomplete, because you’re limited to the ductwork you can easily see and access.

The solution here? If you suspect duct leaks, get a professional duct leakage test. 

It requires special equipment and is performed by professionals—often as part of an overall energy audit—but it’s worth it to know for sure where your air leakage issues are. 

(See where to get an energy audit in your area.)

Back to top

How much energy does duct sealing save? (How much are your leaky ducts costing you?)

The potential energy and financial savings from duct sealing are huge. 

According to ENERGY STAR, if you seal your ducts correctly, you could reduce your house’s energy usage by up to 20% (2). 

If you seal your ducts correctly, you could reduce your house’s energy usage by up to 20%.


Let’s see some numbers behind that percentage. 

Let’s say, on average, about $350 per month of your utility bills goes to heat and cool your home alone. (This example isn’t accounting for other costs that show up on your gas or electric bills, like hot water use or refrigeration). 

Duct sealing could cut your energy waste by up to 20%… that could mean you could bring down your bill to $280 per month. That really adds up.

What to do with that extra cash? Reinvest it in the comfort and efficiency of your home. Get powerful energy upgrades at no upfront cost with Sealed… and pay us with one of the flexible payment options that’s best for you.

Plus, those savings keep growing if you combine duct sealing with other energy-saving strategies. 

Throw in air sealing, proper attic insulation, and energy-efficient heat pumps, and you could cut your energy waste by up to 50%.

In fact, we rarely recommend duct sealing by itself at Sealed, since whole-home air sealing is so important to overall energy-efficiency and comfort.

(Tap here to see if you qualify for whole-home weatherization upgrades—including air sealing, attic insulation, and duct sealing—at NO upfront cost.)

It’s a bit unfair to only talk financial benefits to sealing ductwork, though, since you’re likely to notice the comfort benefits first, such as:

  • More even heating and cooling
  • Much less dust in your home
  • Significantly improved indoor air quality

Not to mention: It’s likely the members of your household will be less grumpy and sleep more comfortably on the coldest and hottest days of the year. And that’s pretty priceless.

Bottom line: Sealing your ductwork has significant efficiency and comfort benefits. 

It’s a worthwhile investment for most folks.

So let’s talk about how to get your ductwork sealed.

Back to top

How to seal ductwork

Seal leaky ducts in a few ways:

  1. DIY temporary duct sealing methods 
  2. Permanent air duct sealing methods 

You’ll cover each route below.

Exposed ducts in central HVAC system are treated with metal tape to eliminate duct leaks

DIY temporary duct sealing

If you saw the word DIY and got excited, you’re likely wondering, “Can I seal my ducts myself?”

The answer? Technically, yes—but with a major exception. 

You’re only going to be able to seal what you can see and access. (And when it comes to ducts, a significant portion of your leakage problem is probably located in places you can’t easily see or access.)

That said, if you want to tackle that part of the job yourself, the first step is to identify all the places where your ducts are leaking air. 

(Tap here for above instructions on locating leaky ducts.)

Then, use either mastic sealant or metal tape to seal those gaps up. 

  • Mastic sealant is a black, pasty product that’s made for air-sealing ducts and can even be painted over. 
  • Metal tape comes in rolls; it seals well but it can be tricky to apply correctly. 

Weirdly, despite the name, duct tape doesn’t last very long on actual ducts. Don’t shoot the messenger.

Weirdly, despite the name, duct tape doesn’t last very long on actual ducts.

All that said, for the vast majority of homeowners, the best way to think of DIY duct sealing is as a stop-gap measure. 

Did you find a major air gap in your ductwork? Then, by all means, buy some metal tape and fix it.

But then—we recommend you call in the professionals. Here’s why.

Permanent air duct sealer methods

There’s no two ways about it: If you want to treat your air duct problems once and for all, you really do need a professional.

Professionals have access to specialized tools and equipment that can detect and treat hard-to-reach duct leaks with much greater accuracy than any DIY method out there.

Even better: They know how to fix your ductwork problems as quickly as possible—with a minimum of disturbance to your home and family life. 

(If you’ve ever seen a “weekend project” turn into a 6+ month slog, you know how valuable efficiency and expertise is when it comes to home improvement.)

But why?

Professionals have access to specialized tools and equipment that can detect and treat hard-to-reach duct leaks with much greater accuracy than any DIY method out there.

One more reason to call in the experts is that they’re up on the latest air duct sealer technology—like Aeroseal, which is (by far) our favorite way to air seal ducts. 

A big factor is that, unlike traditional methods of sealing ducts, Aeroseal does not require any cutting or tearing apart of existing ductwork. 

Instead, it uses a hot polymer glue to seal your ductwork from the inside out—a revolutionary technology that can seal even the smallest holes in your ductwork. 

Because of its unique approach, Aeroseal is easier and less invasive than other duct sealing methods, and it’s usually more effective in sealing off leaks. 

Importantly, Aeroseal is also non-toxic, making it safe for use in homes with children or pets.

Aeroseal is just better technology all around, and it’s definitely not the kind of thing you can apply yourself. (And Aeroseal isn’t paying us to say this! We just find this is a truly powerful, worthwhile home upgrade for our customers.)

The biggest reason to call in sealing experts, though, is that duct sealing is just one small piece of the home-air-sealing puzzle. 

man is air sealing using caulk around windows

If you want the most bang for your duct-sealing buck, you need to seal the rest of your house, too. 

And that’s definitely a job for a professional.

You can click here to get the full scoop on why whole-home air sealing is your best bet for making your house more efficient, but here’s the quick version.

Your house is full of holes—in the ductwork, yes, but also around the foundation, in the attic, and around your windows and doors. 

Some of those holes are visible to the naked eye. Many are not. 

But whether the gaps are visible or not, they’re almost certainly responsible for a lot of energy waste in your house. Up to 15%, in fact, according to ENERGY STAR (3).

Home air leaks and insufficient insulation wastes up to 15% of the energy you buy to heat and cool your home.


(Related: Here’s how to find air leaks in your home)

Frankly, most houses in the U.S. are letting in a ton of outside air—and that’s causing a whole host of problems—from uneven cooling and drafts to super-humid houses that just never seem to dry out.

The solution to this energy loss is to get your whole home professionally air-sealed—ducts and all.

If that sounds intimidating, it doesn’t have to be. Call in the experts—that’s what we’re for! 

In fact, if you go with Sealed for your home upgrades, we’ll plan and oversee the whole project.

Basically, we’ll do all the stuff you don’t want to do so you can get the upgrades you need for your family’s health and comfort.

But should you bother? 

Back to top

Final verdict—Is duct sealing worth it?

In most cases, yes. 

If you’ve got older ductwork that hasn’t been treated in a while, getting a professional to seal it up can have a significant effect on your home’s energy usage (not to mention comfort!).

That said, your ducts are only one section of your home—and sealing air ducts while ignoring the other air gaps in your home is like leaving the majority of your windows open and then wondering why wasps keep flying into your house.

Sealing air ducts while ignoring the other air gaps in your home is like leaving the majority of your windows open and then wondering why wasps keep flying into your house.

Basically, when it comes to home air sealing, here’s a good rule of thumb: If you’re going to seal something in your house, then you might as well seal everything

That’s the only way you’ll get the most efficiency and comfort for your home upgrade money.

The good news here? 

If your house qualifies, you might be able to get a complete home air sealing package (including duct sealing and insulation upgrades) for ZERO money upfront.

Get whole-house air and duct sealing—for NO upfront cost

Yes, really. Here’s our 10-second spiel for how it works.

If your house qualifies for a Sealed energy makeover, you’ll get a free expert energy assessment of your home—and we’ll create a customized plan for your energy upgrades. 

You’ll learn exactly what you need for a more efficient, comfortable home (such as whole-home air sealing, duct sealing, or attic insulation—whatever’s necessary for your situation!).

By the way, we never push anything you don’t need. If a new energy-efficient heat pump is right for you? You got it. If you don’t need new HVAC, skip it for now. 

After you approve the upgrade plan, we’ll hire and vet the best local contractors and manage the entire project from start to finish. 

After you approve the upgrade plan, we’ll hire and vet the best local contractors and manage the entire project from start to finish. 

Then—after we make your house more comfortable, more energy-efficient, and the envy of your neighbors—you’ll pay for the work done with one of the flexible payment options that’s best for you. 

(Learn how the payment plan works.)

Sound intriguing? Want to see if you qualify? Answer our 2-minute questionnaire here.

If I don’t have to spend any extra money to get a huge improvement to my home, it’s just a no brainer at that point.

Scott. R, Sealed customer
April 7, 2023