How to Seal Your Ductwork: 3 Simple Methods

Sealing ductwork is essential to an energy efficient heating and cooling process.  If your ductwork is not sealed properly, you are losing money on heating and cooling bills – like leaving a window open when the heat is running or the AC is trying to cool and dehumidify your home. 

The ductwork in your home carries either hot or cool air from your furnace air handler to all the rooms in your house.  Leaks, according to the Department of Energy, can cause up to 30% of the air to be lost. Besides a huge waste of money, some rooms in your home may not be getting enough heated or cooled air. 

See our Guide on How to Check Your Ductwork for Leaks, and inspect your ducts every year or so. Do it immediately if you hear whistling coming from the ducts, indicating an air gap, or if your energy bills suddenly go up for no reason that you’re aware of. When inspecting your ductwork, start at the furnace and follow the ducts throughout the home.  It is a good idea to either take note or take a picture of any areas that will need sealing.

There’s a section below called How Do I Know My Ductwork Needs to be Sealed? It’s a good place to start if you’re unsure duct sealing is the issue you’re having. 

What are the Best Methods to Seal Ductwork? 

There are a few methods considered best practices for sealing ductwork leaks. Each method has positives and negatives.  When deciding which method to use please carefully consider the following information about your options for sealing ductwork.  The best methods are the following:

  1. Short-term (Up to 7 years): Foil HVAC Sealing Duct Tape – As the name suggests, duct tape is an option to seal any leak in your ductwork system. This type of tape is also known as aluminum or foil tape. You can purchase duct tape at any hardware store or home improvement retail store, and it is available online. 

This tape IS NOT the generic duct tape that is widely available and made of cheap plastic. Foil tape is the good stuff. It is rated for actual use on ducts.  DO NOT USE REGULAR DUCT TAPE ON YOUR DUCTWORK!!  Also, make sure whatever heat-rated type of duct tape you decide to use has the UL label on it.  The UL label stands for Underwriters Laboratory.  The UL label ensures that the duct tape is for use on ductwork systems.  Using properly rated duct tape is not messy at all and is very easy to work with.  However, using the proper duct tape to seal the leak or leaks in your duct system is not a long-lasting fix.  Eventually, the duct tape will become old and detach from the duct that it is supposed to be sealing.

  1. Long-term (15-25 years): Mastic / Duct Sealant – Mastic or a similar sealer is a more cost-effective and longer-term solution to seal your ductwork, compared to foil duct tape.  Mastic and latex sealant is a water based, paste-like substance that hardens after you apply it to your ductwork. It is fiber-reinforced for strength and toughness. You can use a paint brush and carefully brush it over the area that is leaking. Here’s one that is easy to work with. 

Another way to purchase and apply mastic is by using a caulk gun and a tube of duct sealant.

Once it hardens, the duct is sealed. It does a great job of sealing any leaks and is not too expensive.  You can expect to buy a half gallon of mastic for ductwork sealing for around $25.  These kinds of sealants will seal a leak that is larger than ¼” in width.

Pro Tip: Leaks a ¼” wide or more have to be fixed. Push the sections together and fasten them with sheet metal screws. If that doesn’t work, then the ductwork was wrong from the start – metal doesn’t shrink that much. If you can’t close the gap, either replace the section (best) or cover the gap with foil duct tape.

  1. Aeroseal / Professional Serivces

Aeroseal is one of the top names in high-tech duct sealing. You probably don’t need this kind of service unless your ducts are really old and are difficult to repair or replace. This is considered internally sealing your ductwork via a technology and is done by a licensed professional.  A technician will block all your vents and a computer will locate all of the leaks that are in your ductwork. Once all the leaks are identified, a mastic duct sealant will be used throughout the ductwork system.  This is the most effective way to ensure that all the leaks are sealed properly. But it is quite expensive. You can expect to pay a lot more than using simply heat rated duct tape or mastic via a brush. 

How Much Does It Cost to Seal Ductwork? 

Sealing your leaky ductwork is not very expensive if you do it yourself.  A 200-foot roll of duct tape will cost around $15.  Depending on the number of leaks that are located in your ductwork system you will likely spend less than $30 to seal the leaks yourself. Plus, if you have tape left over, you’ll find common household fixes to use it for.

Mastic is a little more expensive than heat-rated duct tape. You buy a half gallon of mastic for $25 and a 2-inch paint brush for $5 or less. By a cheap one, or two, and throw them away rather than trying to clean them.  The overall cost to seal the ductwork by using mastic will cost you a total of around $50.  Mastic will last a lot longer than duct tape, but it will also take longer and is a bit messy. 

Internally sealing your ductwork is a very expensive process.  You can expect to pay around $2,000 to hire a company to come out and seal all the leaks within your ductwork.  This is the best way to make sure that all your leaks are properly sealed, and you don’t have to worry about missing any leaks.  Internally sealing your ductwork will improve the efficiency of your heating and cooling system, and it will also improve the air quality of your home.

How Do I Know my Ductwork Needs to be Sealed?

Having leaks within your ductwork system can result in a loss of 20-30% of treated air and a higher energy bill. It’s not very green either. 

If you suspect that your ductwork is leaking, then you should look into sealing the ductwork by either doing it yourself or hiring an HVAC technician to do the work.  Below are a list of things to look for if you suspect you have leaks within your ductwork:

  • Higher-than-normal heating or cooling bills.
  • Uneven heat within various parts of your home.  For example, your living room is at a normal temperature, but a bedroom is much colder or much warmer.
  • Visible gaps or tears in your ductwork.
  • Whistling or whooshing sounds made by air being sucked into return ducts or being pushed out of supply ductwork.
  • Some of the ductwork is either kinked or twisted.

Frequently Asked Questions

Maybe you have one or more of these duct sealing questions we get asked a lot:

How long does it take to seal my ductwork?

You can expect it to take a good day’s worth of time to seal your ductwork yourself.  This includes cleaning the exterior of the ducts, as needed, and then either using heat-rated duct tape or mastic with a paint brush or a caulk gun.  

Is sealing my ductwork something I can do on my own?

Sealing your own ductwork is definitely a DIY project if you don’t mind a little hard work and getting dirty. The most difficult part is locating the leaks. 

How much does it cost to seal my ductwork?

If you seal the ductwork yourself, the supplies will cost you around $50 or so for all the materials needed to make your ducts energy efficient. This method pays for itself in a month or two of lower heating/AC costs. Hiring a professional company to internally seal your ductwork will cost $2000. Put it this way. Let’s say you lose 25% of heated and cooled air through leaks – it doesn’t get where you want it to go, so it is wasted, and the money is lost. If you spend $2,400 per year on heating and AC, that represents a loss of $600. That means it would take you 3-4 years to pay for the extra cost of hiring a company like Aeroseal to seal your air ducts.

How do I know that I need to seal my ductwork?

There are many ways to identify that your ductwork needs sealing.  Higher than normal heating costs, feeling or seeing leaks, etc. are all ways to know that your ductwork will require sealing. See the list immediately above the FAQ section.

What is the best way to seal my ductwork?

The overall best way to seal your ductwork is to hire a professional to do the job by internally sealing your entire ductwork system. However, if your ductwork is accessible, and you enjoy homeowner projects, then we recommend buying mastic, cleaning the outside of the air ducts, and applying mastic. Skip the pros. 

DIY or Hire a Professional?

If you suspect that your furnace is not properly working or that some areas of your home are not the same temperature as other rooms, then you probably have some leaks located in your ductwork system.  Sealing the leaks on your air ducts is something that you can do yourself by using foil or aluminum duct designed specifically for use on ducts. A more permanent option is to apply mastic that is made for sealing ductwork. 

You will have to locate the various leaks and then simply seal them up by using one of the two methods.  If you are not a hands-on person and don’t feel comfortable sealing your own ductwork, then you have two options.  You can hire an HVAC technician to come in and inspect your ductwork and then they can seal the leaks as needed.  You can also hire a company to internally seal the leaks within your ductwork system. 

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