HVAC technicians have bags, chests, and truck beds full of tools. Each one serves a purpose, and almost all of them are a required element of the technician’s arsenal. One of the most overlooked tools of the trade is duct tape and mastic sealants.
This article will cover the various sealants needed to prevent or repair HVAC ducting leaks, why you should never use Duck Tape brand tapes (non-HVAC rated) and offer you the 8 best HVAC duct tape and mastic sealants, reviewed and compared. Read on to find out what should be in your HVAC tool kits.
Quick Guide – Our Top Picks
Best Mastic Sealant
Best HVAC Tape
Best Mastic Tape
Why HVAC Technicians Use Tapes & Sealants
Heat and cold cycles used over throughout the year will cause any material to expand and contract. HVAC ducting is no different. Over time, the connections, seams, and splits can warp, separate, or produce holes. These areas will let air out, causing your system to have to work harder or longer, raising your energy bill and lowering the efficiency of your system.
Instead of replacing the entire ductwork, it is more economical and faster to patch the hole with a proper taping or sealing method. HVAC ducting sealants work just as well (or in some cases better) than the material the duct is made from, which can maintain your warranty, lower your energy bills and raise your system efficiency.
HVAC Duct Tapes Compared
Choosing a Quality HVAC Tape & Mastic Sealant
What is it that makes a good HVAC tape? Below we offer you a brief buyer’s guide of various factors to look out for, take notice of and keep in mind when shopping for your next tape or sealant.
Width & Thickness of Tape
One thing you need to check is how thick your tape is. If your repair area is wider than your tape, it may not seal properly, even if you layer the tape. Ensuring you have tape that is wide enough will go a long way to making better repairs.
Features
HVAC tape has certain features that you need to pay special attention to. Here are the important aspects.
- Temperature Rating
HVAC systems go through extreme temperature changes. Most residential installs have components in the attic which can reach excessive temperatures. The steel or aluminum ducting can get overheated or under-cooled, too. Your tape needs to be able to handle the drastic temperature ranges. - Conductivity
Conductivity can be important in the HVAC repairs. Thermal conductivity will allow you to use the tape in areas that go through temperature changes without swelling or constricting, which maintains the integrity of the repair. - Water Resistance
While not the most essential aspect, the HVAC tape and sealant need to have good water resistance. HVAC systems, especially the ducting, can hold moisture and humidity. Tape that isn’t resistant will wear, puncture or lose its adhesion fast.
Backing & Adhesive
There are several backing materials used in HVAC tape, including aluminum, vinyl, foil, fiberglass, and paper. The backing will determine the proper use of the tape. In this case, aluminum, foil, or fiberglass work well for ducting as they have the general conductivity properties needed to withstand the various temperature changes.
The type of adhesive is also important. Acrylic is most often used because it has lower fire properties and doesn’t wear with drastic temperature changes. Add acrylic and aluminum or foil backing, and you have a weather-resistant, fireproof tape that meets UL code (more below) for use in all HVAC systems.
Permeability
When searching for the right tape, you will want to find one that has a low permeability rating. Permeable tapes will allow gases and liquids to pass, including air, which is what you are trying to prevent.
This doesn’t mean permeable tape doesn’t belong in your HVAC tool kit, but for ducting work, it isn’t the best option.
Adhesion
Most HVAC rated tapes will have the same level of adhesion. However, different types of adhesives will stick better or seal longer than others. For ducting, you will want a medium adhesion so that you can reposition the tape a few times if needed.
If the adhesion is too high and you misalign the tape, you will have to start over with a new piece. While it may not seem like much of a waste, over time, the cost of that wasted tape can add up.
Tack and Strength
Tack is the rating of how well the tape will stick when applied. The higher the tack, the more instantly it bonds with the surface. The tack coincides with the strength of the tape. Higher tack tapes are stronger and will last longer, but are less forgiving to molding to corners and some angled edges.
Conformity
In a perfect world, all ducting would be straight, level, and only contain right-angles. However, this isn’t the case. You need your tape to be able to form and conform to various shapes, sizes, and angles to get the job done.
If a tape it too stiff, for example, you will find that you need multiple pieces in much shorter cuts to make it work. Having too many pieces is grounds for failure along the seams at some point.
Code Compliance
You must maintain code compliance for all things in your home. One of those compliance standards is fire prevention. The Underwriter’s Laboratory (UL) rates items and tests their ability to withstand, prevent, or help control fires, water leaking, and other things.
For ductwork to be in compliance, it must meet UL code 181 (A-rigid ducting or B-flexible ducting). This means that when you do a repair, the repair must also meet UL requirements. The tape used in your repairs must be UL 181A or UL 181B compliant for it to be allowed for use.
Application Technique
Your HVAC compliant tapes are considered “pressure-sensitive.” This means that you must pay the tape in place and then use pressure to force the adhesive to stick in place. You can use many different types of pressure tools to complete the job.
The most popular tool is a squeegee, though rollers, gloved hands, and even a soda bottle can be used. As long as the tool fits in the area and can press into the corners and edges for a tight, proper seal, you will be fine.
8 HVAC Tape & Mastic Sealant Reviewed
HVAC tape and mastic buying don’t have to be a painful process. Below we offer you the 8 best HVAC tape and mastic sealants reviewed and compared. We are confident your next HVAC tape purchase is on this list.
1. TapePlus Professional Grade
Best HVAC Tape
| Roll Dimensions | 2-inches x 70 yards |
| Best Used For | Rigid ducting, Hot/Cold inlets |
| Resistant to? | Moisture, UV rays, flames, chemicals, mold and weather |
| UL Listed? | No |
| Temperature Range | -20 – 180 (F) |
The best foil tape for HVAC tape is easy to use, strong, and resistant to almost every environmental factor. TapePlus Professional Grade Aluminum foil tape is all of that and more. The 2-inch wide tape will seal almost any small or medium-size hole, warp, or seam separation.
The acrylic adhesive is pressure-sensitive, and if the surface is clean, the tape will stick. The TapePlus roll will adhere to plastic, metal, steel, aluminum, tin, fiberglass, and most other clean surfaces.
You also get 70 yards per roll, which is more than the industry average, offering you plenty of tape to seal your entire HVAC system with ease. The tape is waterproof, fire, and chemical resistant and also resists mold, mildew, and UV rays.
One of the highest rated, most reviewed, and purchased HVAC tapes will stick where others won’t, go where others can’t, and provide you with years of permanent repair in your heating and cooling ductwork, no matter the cause or reason for the leak.
Pros
- Simple application to almost any surface type.
- Seals gaps, holes, and warps in seams or ducting in extreme temperatures.
- More tape per roll than most other options.
Cons
- While it is compliant with all UL 181 requirements, it isn’t UL listed.
2. Red Devil 0841DX F Seal 181
Best Mastic Sealant
| Roll Dimensions | 10.1 ounces or 1 gallon |
| Best Used For | Flexible ducts |
| Resistant to? | Mold and mildew resistant |
| UL Listed? | UL 181A and UL 181B |
| Temperature Range | -25 – 200 (F) |
Red Devil offers you one the best mastic sealant solutions around. Available in two sizes, this mastic is ideal for all manner of HVAC air leak repairs. It is thick and easily applied with a paintbrush or putty knife. It will flow into corners and creases, too.
Red Devil F seal is flexible, resistant, and perfect for indoor or outdoor use. It isn’t as UV resistant as some of the tapes, but in most cases, this only affects the finished, dried coloring of the mastic. The quick-drying formula doesn’t drip as much as some of the other mastics on the market, either.
You can easily apply a smooth, even coat with just a little effort. For larger tears, holes, or gaps, a mesh screen will hold the mastic in place until it dries. Once dry, the mastic will perform just as well as the duct itself, even through heat and cold cycles.
If you have minor areas, the mastic may not be your best option. Instead, a good HVAC tape should be used. However, for hard to reach areas, it can be a simpler application process than trying to get the tape to conform to the tighter area.
The F seal is UL rated for 181 A and B and will hold up to high temperatures, freezing temperatures, and frequent changes in the duct temps and flexing. For all general applications, there are few better options for you to choose from. If you need mastic, Red Devil is the answer.
Pros
- Easy to apply
- Fast drying and less spilling
- Perfect for flex ducting
- Works indoors or outside.
Cons
- Not as resistant to environmental factors as others
3. 3M Scotch-Seal Mastic Tape Compound 2229
Best Mastic Tape
| Roll Dimensions | 1, 1.5 or 3.75-inches X 10-foot |
| Best Used For | Flexible or rigid ducts, Hot/Cold inlets |
| Resistant to? | Moisture, mold, mildew resistant |
| UL Listed? | No |
| Temperature Range | -25 to 195 (F) |
If you are looking for a mess-free mastic option, mastic tape is the answer. 3M Scotch-Seal has a mastic tape in three sizes that will easily conform to any shape or angle without the need for brushes and putty knives.
With an easy-peel paper backing, you can control exactly how much mastic is used and where it goes. The tape cuts well with a knife, scissors, or a putty knife, too, so you don’t need to worry about tearing it pulling off too much.
This mastic is moisture, mold, and mildew resistant and won’t warp or disintegrate due to heat and cold cycles. However, this tape is slightly flammable and doesn’t mix with chemicals well. It isn’t UL listed, for this reason, so care should be used when applying.
You need to ensure the area is clean and free of grease, debris, dirt, or residue. However, this mastic is also electrical safe. You can use it to wrap, insulate, or pad electrical systems. Make sure you cover the mastic with a UL approved electrical tape.
Pros
- Easy to apply in any conditions
- Withstands high temperatures without deforming.
- Can be used as an electrical insulator
Cons
- Not fireproof
- Not UL listed, but is RoHS 2011/65/EU compliant without exemption
4. 3M Aluminum Foil Tape 3340
Highly Rated
| Roll Dimensions | 2.5-inches x 40 yards |
| Best Used For | Rigid ducting, seams, fiberglass or aluminum board ducting |
| Resistant to? | Moisture, UV rays, flames, chemicals, mold and weather |
| UL Listed? | UL 181 A and B listed |
| Temperature Range | -40 to 300 (F) |
One of the highly rated foil tapes is the 3M Aluminum Foil Tape series 3340. This tape does it all. It is easy to apply, has a strong acrylic adhesive, and will stick to almost anything. Whether your gap is small, medium, or needs multiple applications, this tape does what you need.
The acrylic tack is extra durable, which is why this tape is so highly rated. The pressure-sensitive tack will stay where you put it. Using a roller, squeegee, or a firm finger, you can activate the adhesive, and as long as the mounting area is clean, the tape will form a permanent bond.
If you ever need to remove the tape, you will need to use a razor and be patient. It will take some time to remove, especially if it has gone through a few heating cycles. However, if you are applying directly and haven’t pressed it into place, there is a little give that allows you to reposition if needed.
This HVAC tape is best used with rigid ducting, though it can also be used on flexible ducting, seams, corners, and even over mounting brackets. Rated for indoor and outdoor use, the construction of the tape will withstand the elements, UV light, fire, moisture, and most chemicals.
If you have extreme temperatures in your area, this is the ideal tape. It has one of the largest temperature ranges (-40 degrees to 300 degrees), so you can feel comfortable using it in any condition.
Pros
- Rated for rigid and flexible applications
- Tack and strength are higher than average.
- Fire and waterproof
- Easy to apply for a permanent bond
Cons
- Not easily removed if you make an error when applying.
- Doesn’t tear as easily as other tapes
5. UNITED STATES HDW KK0326
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Best Water Based Duct Sealant
| Roll Dimensions | 64 ounces |
| Best Used For | Flexible ducts, fiberglass board ducting |
| Resistant to? | Heat, cold, moisture, mold and mildew resistant |
| UL Listed? | UL 181 A and B |
| Temperature Range | -20 to 195 (F) |
The best water based duct sealant is hands down the United States HDW mastic. Not only does it apply evenly and accurately, but there are zero VOCs. It is also rated for indoor and outdoor use. As long as the temperature is above freezing and it isn’t raining, you can apply the mastic at any time.
This 64-ounce container holds enough mastic compound to fix every leak you have. For larger areas, you will need a screen mesh. However, depending on the application size and the type of mesh you are using, you will most likely need multiple coats to get a complete seal.
For flexible ducting, the US HDW is ideal. It will conform to all angles and doesn’t drip or run like others can, even at high temperatures. It is UL listed 181 A and B, so your projects will stay within code, and you can save a lot of money by doing simple leak repairs on your own.
The best application method is with a trowel or putty knife. However, you can use a caulking gun, brush, or roller. Apply the mastic to all seams, gaps, and mounting locations in supply and return ducts as well as joints in metal, fiberglass and flexible ducting.
The mastic does take a while to dry. If you need to do multiple coats, it may be best to set aside a couple of days and give each layer time to cure completely before applying the next coat. The good news is that with this brand, you won’t need gobs of the material to seal a leak. Thin layers work just as well and last just as long as the thicker coats required from other brands.
Pros
- No-drip application even in hot temperatures
- Can be applied even in sub-zero temperatures
- Zero VOCs
Cons
- Can take a while to dry between applications
- May require multiple layers to seal properly
6. Shurtape AF 100
Thick Tape (2.8 Inch)
| Roll Dimensions | 2.5 or 2.8-inches x 60 yards |
| Best Used For | Flexible ducts, fiberglass board ducting |
| Resistant to? | Mold, mildew and water resistance |
| UL Listed? | UL 181 A and B |
| Temperature Range | -20 to 260 (F) |
Shurtape AF 100 is a thick tape for general applications when you need to cover a larger surface area. Many leaks are in awkward positions or on flexible ducting that requires multiple layers of sealant.
With the Shurtape, this thick tape (2.8 inches) will keep you from having to overuse the tape while still having enough solid ducting material to adhere to. The butyl adhesive has a high tack and is very durable. The tape itself tears easily, so you don’t need to find a knife or scissors to get the job done.
This tape doesn’t hold up to the elements as well as acrylic adhesive tapes do, but it is still rated for indoor and outdoor use. When using outdoors, though, it is best if the area is covered or in an area that doesn’t get direct rain, sun, or exposure.
Unlike foil tape, this tape doesn’t hold up well to flames. However, if your ducting is on fire, the tape is the least of your concerns. Care should still be used when applying. The tack is pressure-sensitive, but it doesn’t take a lot of pressure. If you don’t get the strip laid right the first time, you may find that you have to start over from scratch with a new piece.
You also need to make sure that the application area is cleaned, dried, and free of chemicals, debris, and grease. Once applied, you will need a razor to remove, and it will last for several years without warping, peeling, or cracking.
Pros
- Comes in two thick-width sizes
- Easy to apply in most conditions
- UL 181 listed to conform to current code standards
Cons
- Not as durable as some acrylic adhesive tapes
- Not as fire resistant as other tapes
7. Duck Brand HVAC Duct Sealing Tape
Trusted Brand
| Roll Dimensions | 1.88 Inches x 30 Yards |
| Best Used For | Flexible ducts, steel, aluminum or tin ducting |
| Resistant to? | Moisture, UV rays, flames, chemicals, mold and weather |
| UL Listed? | UL 181 B listed |
| Temperature Range | -20 to 200 (F) |
Duck Brand HVAC duct sealing tape is one of the most trusted brands. And while their “Duct Tape” line isn’t designed for HVAC applications, this particular line is one of the best for the job. As long as you don’t confuse the two, you can seal your ducting leaks and make beautiful Duct Tape belts or bracelets.
The tape is thinner than others on this list, but at almost 2 inches, you won’t have much trouble repairing your leaks. Ideal for flexible ducting, fiberglass boards and even some rigid ductwork, the Duck brand has you covered.
The tape tears easily, which is nice for applications, but can be problematic when you have to cover mounting bolts or sharp edges. In these instances, it is recommended that you use mastic instead of tape. However, you aren’t required to use the Duck brand with mastic in normal situations.
The tape is also UL 181B listed for fire resistance on flex applications. You will also find that the tape is indoor and outdoor rated for all general applications. It is UV resistant and holds out water and nature with ease.
If your HVAC flex ducting has a tear or a leak, the Duck brand HVAC duct tape will have you back to 100% efficiency in no time, without the need for a professional HVAC technician.
Pros
- Ideal for all HVAC flex ducting
- Doesn’t require mastic for use
- Multiple layers won’t leak at seams
Cons
- Tears a little too easily
- Can be too thin for some applications
8. Hardcast Rolled Mastic Duct Sealants Foils
Best Tape For Flexible Duct
| Roll Dimensions | 3 inches x 33 yards |
| Best Used For | Flexible ducts |
| Resistant to? | Moisture, UV rays, flames, chemicals, mold and weather |
| UL Listed? | UL 181B Listed |
| Temperature Range | -25 to 295 (F) |
For those with flexible duct, the best flex duct tape is the Hardcast Rolled mastic foil. This roll is a mastic-tape hybrid that has instant adhesion. You don’t need to press it into place to activate the mastic adhesion, which comes in hand for hard to reach areas or for flex ducting that won’t handle the pressure from a squeegee.
There are other applications, as well. Not only can you use this almost anywhere in your HVAC system, but it also seals PVC and some electrical applications (electrical tape cover is required). The Hardcast roll is also UL 181 B rated for flex duct fire resistance.
The mastic duct sealant foil is also UV resistant, mold and mildew resistant and will hold up to water, moisture, most chemicals, and any weather conditions. Rated for indoor or outdoor use, you can apply this anywhere you have an air leak.
One thing to note, though, is that this mastic tape is hard to remove. If you are using it for a temporary repair, you will need more than a razor for removal. Plan on spending more time removing the adhesive with chemicals, hot soap and water, and a lot of elbow grease.
In permanent applications, though, you can apply the tape and then forget about it. It will stand the test of time and most likely outlast the ducting that it patches.
Pros
- Best for flexible ducts
- Indoor or outdoor use rated
- Seals PVC as well
- No VOCs
Cons
- Instant adhesion requires a steady hand for proper application
- Doesn’t come off easily
Types of Duct Sealing Products Explained
For sealing ducts in your HVAC system, there are a few methods you can use. Depending on the size of the patch, the location of the leak, and how accessible it is, one method may be more suitable than others.
Duct Mastic/Mastic Sealant
Mastic is a paste that is applied to larger holes or gaps. Before using mastic, you will need a mesh screen to cover the hole and an area for the mastic to adhere to. The mastic putty is brushed, rolled, or knifed on to cover the screen, the duct surrounding the screen, and the gap. It will dry, harden, and seal for a permanent solution.
Foil-Backed Tape
For smaller areas, small seams, or tight corners, foil-backed tape is used. The adhesive properties will attach semi-permanently to the surrounding duct area and effectively seal off any small holes, cracks or warped seam separation.
Injected Aerosol Sealant
Occasionally, the ducting behind the walls or in the ceiling will get a leak that isn’t easily accessed. Once the leak is found, the best method of sealing is to use injected aerosol sealant. With the system running, the aerosol is sprayed into the ducting to seek out any gaps, leaks, or cracks.
It will fill the holes, harden and last as long as your ducting. It is ideal for hard to reach or impossible to access areas that need small repairs.
How to Find Ductwork Leaks
In most instances, it is best to call an HVAC technician to diagnose and detect leaks. A leak in the duct may be a sign of other issues that should also be addressed. However, there are methods you can employ to check for leaks yourself before making the call.
The first step is a visual inspection of your ductwork. You are looking for areas of damage or old sealing methods. If you see tape or patches, they have likely begun to leak themselves. You can also use your hand or a source of visible smoke (incense, candle, etc.) to see when the air leaking causes the smoke to move or swirl.
A technician will be able to use a smoke machine or perform an air pressure test to find where and how bad the leaks are in a more accurate and efficient method. If you suspect a leak, it is best to call a professional.
How to Effectively Use HVAC Tapes & Mastic Sealants?
To be effective, mastic and tapes need to be applied correctly. While it may seem simple to find the leak and throw a piece of tape over it, there is a lot more to it. You need to ensure that the tape or adhesive will stick and that it will maintain integrity during use.
Before you apply the sealant, you need to clean the area thoroughly to remove any previous adhesive, dirt, dust, or grime. Failure to clean properly will result in air holes, loose adhesive, or the tape not sticking at all.
Applying the mastic or tape will depend on the location and type of hole or warp. You want to make sure you can cover the area with a single width of tape, as multiple layers will create spaces for the air to escape. If you need to use mastic, a mesh screen needs to placed over the hole first to allow the mastic to adhere properly and cover the entire area.
Proper HVAC Tape Storage
HVAC tape can spoil. Not to the effect of that gallon of milk in your fridge, but it can lose its ability to seal properly. The average shelf life of HVAC tape is about a year. If your roll is older than that, you need to replace it.
Rolls should get stored on their sides, sticky edges facing up. If you let them stand on the backing edges, the roll can warp, making it difficult to unroll. You should also avoid stacking rolls on top of each other or placing them in areas that are hot, humid, or change temperatures constantly.
People Also Ask (FAQs)
What is aluminum foil tape and what is it used for?
Aluminum foil tape is a foil-backed adhesive tape used to seal seams and small gaps on fiberglass boards and aluminum boards in HVAC ducting. Because it is reflective, UV resistant, and conductive, it is also used as shielding and for thermal insulation.
What kind of tape do you use for ductwork?
The most common type of HVAC tape used is foil tape. Foil tape uses acrylic adhesive to prevent degrading due to heating cycles, and it doesn’t become brittle or lose the backing over time. For larger ductwork issues, screen mesh and mastic are used instead of tape.
Is HVAC tape waterproof?
Not every HVAC tape is waterproof, but almost all of them are. Waterproofing, fire resistance, and UV resistance is the primary design of all HVAC tapes because of their uses and applications.
Why does Duct Tape not work on ducts?
Duct Tape brand tapes are not designed for HVAC ducting. The name is confusing but is considered to be an artistic tape, not a functional tape. While the adhesive is strong and the vinyl backing comes in a lot of widths and colors, it cannot stand up to the constant and drastic temperature changes or air pressures in HVAC duct systems.
What is the best way to seal ductwork?
The best method will depend on the size of the leak, its location, and where the duct is located. For easy to reach and access leaks in ducting or fiberboard seams, a foil or aluminum tape with acrylic or butyl adhesive is best. If the hole is larger, a screen mesh painted over with mastic is preferred. If, however, the leak is behind the walls or in the ceiling, an aerosol mastic is preferred to run through the system and seal the leaks you cannot easily access.
Do I need a professional HVAC technician to seal the leaks in my duct system?
An HVAC technician is not required to apply sealant or tapes to duct leaks. However, you may need to hire a professional to locate all of the leaks, perform air pressure tests or smoke machines. A technician will also perform general maintenance and inspections while there, which can save you money by locating other problems with the system before they become significant or costly.
Conclusion
Air conditioning duct tape is a tool that every HVAC technician and homeowner should have in their tool kits. It can be challenging to decide which types or brands to go with. If our guide hasn’t given you the obvious best choice for your needs, we suggest you go with our top pick.
The TapePlus Professional Grade Aluminum Foil Tape is designed for all types of HVAC work, has excellent adhesion, tack and strength, and is weatherproof, fireproof, and UV resistant.
