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Duct Tape | Can It Be Used on HVAC Ducts?

Oh, blast it! You’ve realized that there’s a small leak in one of your HVAC ducts, and you want to seal it up fast. However, the only thing you have in stock is duct tape, and you’re not sure if it will do the job.

The name of duct tape is extraordinarily misleading as it is actually inappropriate for fixing leaks in ductwork, like that serving your HVAC system.


Duct tape cannot withstand extreme temperatures, and HVAC ducts carry hot/cold air. Duct tape is not waterproof, and HVAC ducts can experience condensation. Both extreme temperatures and moisture compromise the tape’s adhesive. In addition, duct tape is not code-compliant for duct repairs.

Duct Tape Can’t Withstand High or Low Temperatures

Duct tape is generally made up of three materials: fabric mesh, polyethylene coating, and a strong rubber adhesive.

The stickiness in duct tape comes from the pressure-sensitive adhesive, which consists of soft polymers that bind objects together through intermolecular forces known as van der Waals forces.

Duct tape components, fabric mesh, polyethylene coating and rubber adhesive

For this ‘sticking’ to work, the adhesive needs to be hard enough to resist movement when stressed but not so hard that it doesn’t maintain the bonds.

Since variations in temperature affect the hardness of materials (which is why things melt when they get too hot or harden or freeze when they get too cold), temperature affects the adhesive quality of duct tape.

It may be easy to get confused about the efficacy of duct tape at high temperatures because duct tape is resistant to high temperatures in the sense that it does not melt or ignite easily.

However, it is not effective at high temperatures because the adhesive will begin to degrade and lose strength.

The adhesive will start to lose function at around 140 ºF, and as temperatures increase from there, the rubber components may also begin to melt.

Similarly, the adhesive will harden at very cold temperatures, which will also reduce its ability to stick.

The lower limits at which duct tape can be used are not as clear, but you may notice a decline in function at around 40 ºF, declining rapidly as temperatures reach freezing point.

HVAC Ducts Carry Hot/Cold Air

The temperature of ducts in HVAC systems will differ depending on where the temperature is recorded, with hotter temperatures occurring near the furnace component or cooler temperatures recorded nearer air conditioner components.

Generally, the air in HVAC ductwork can reach temperatures between 140 ºF and 170 ºF. The ducts themselves might not be quite this high, but since there is a break in the duct that you are trying to fix, the duct tape will be exposed to this air directly.

In the case of cold air, it is less likely that the ducts will reach temperatures close to freezing.

This is because the air carried in the ducts from the air conditioning unit should be 15-22 ºF cooler than the air coming into your house, and if you are using air conditioning to cool down your home, it is unlikely to be freezing cold outside!

Nevertheless, duct tape is not suitable for use on HVAC ducts because of the high temperatures that it would be exposed to.

Exposure to Moisture Degrades Duct Tape Adhesive

Duct tape is water resistant as a result of the polyethylene that coats it.

In fact, before duct tape was commercialized as ‘duct tape’, it was given the nickname ‘duck tape’ because of the way water runs over it like it does over a duck’s back.

The Original Duck Brand 394475 Duct Tape, 1-Pack 1.88 Inch x 60 Yard Silver

These days, this causes some confusion because there is a brand called Duck Tape that sells a range of tapes, including what we know as duct tape. So, technically, calling it duck tape is not wrong, but there are differences.

Due to the water-resistant properties of duct tape, one would think that it would be useful even in instances where moisture is present.

However, duct tape is resistant to water; it is not waterproof. There’s a pretty significant difference.

It means that while the tape might be useable where a little bit of moisture is present, this is only the case for a short period of time, and before long or with large quantities of water, it becomes ineffective.

The reason for this is that the moisture weakens the stickiness of the adhesive part of the tape.

Without the adhesive, the duct tape cannot stick and carry out its main function.

Condensation Can Form on HVAC Ducts

Condensation should not be the norm for an HVAC system that is functioning well. However, it can form on HVAC ducts, particularly those with air leaks.

Air holds moisture as water vapor, and when warm air holding moisture is suddenly cooled when it comes into contact with cooler air or a cold surface, the water vapor changes from a gaseous state to a liquid state, forming the little drops of water known as condensation.

Condensation is basically the opposite of evaporation, which is when water is heated up so much that it becomes a gas (water vapor).

In HVAC ducts, condensation can occur if there is a big difference in temperature between the air inside and ducts and the air outside, and your ducts are not well insulated.

For example, if the air inside HVAC ducts is very cold and the air outside is warm, droplets of condensation can form on the outside of the ducts.

In HVAC ducts, it can also be caused if your HVAC system is overcooling the air or not removing moisture sufficiently.

Either way, since condensation can form on HVAC ducts, and duct tape is not waterproof, you can see why you shouldn’t use duct tape for HVAC ducts.

HVAC Tape Is Regulated by the Building Codes

The requirements for sealing joints in HVAC ducts are listed in Section M1601.4.1 of the International Residential Code (IRC).

In this section, it states that tapes used to seal ducts need to fulfill a UL 181A listing.

Man using duct tape in ducts

If a tape has received a UL 181 listing, it means that it has undergone various tests.

These tests determine to what extent the tape is resistant to fire, mold, and humidity, and also test its resistance to variations in temperature, pressure, tension, and leakage, among other factors.

The code mentions UL 181 A-P and UL 181 A-H tapes for sealing fibrous glass ductwork, and UL 181 B-FX for metallic and flexible air ducts.

The UL 181A listing indicates that the tape needs to have passed more stringent testing requirements.

In addition, the UL 181A listing requires that the tape must be made with a release liner, made of aluminum or a similar alloy, and be at least 2.5″ wide.

Tapes meeting the UL 181 B-FX listing are at least 1.825″ wide, but can be made from cloth, film, or foil.

It is clear from these regulations that duct tape does not meet the requirements to be code compliant.   

What to Use Instead

So, we have established that duct tape is not a safe option when it comes to repairing leaks in HVAC ducts.

Thankfully, there are a number of other tapes and products that are safe for you to use!

Firstly, you can use aluminum foil tape (amazon link), which has a durable acrylic adhesive and is resistant to temperatures ranging from -40-300 ºF.

3M Venture Tape UL181A-P Aluminum Foil Tape 1581A, Rigid and Flexible Duct Seaming, Durable, Cold Weather Adhesion, 3.89 in x 60 yd, 2 mil

This tape is listed for UL 181 A-P and UL 181 B-FX, and there are ranges of brands and options to choose from.

Another option is butyl rubber sealant tape (amazon link). This may not be appropriate for the UL 181A listing, but it is listed for UL 181 B-FX.

If you are willing to move away from using tape, another good option is fiber reinforced water-based duct sealant (amazon link).

Although it may be a bit messier, it can be applied in hard-to-reach places and should dry quickly. It is also UL 181A and 181B listed, so it can be used on all types of HVAC ductwork.

Whatever tape or sealant you decide to use, just remember to make sure that it is code compliant.

Sources

https://firefighternow.com/is-duct-tape-really-flammable/

https://www.echotape.com/blog/the-complete-technical-guide-to-duct-tape/#fails

https://escholarship.org/content/qt1f27h40p/qt1f27h40p.pdf

https://hvac-boss.com/faq/how-hot-can-ductwork-get/

https://www.bluenationalhvac.com/air-conditioner/ac-temperature-differential/

https://www.thoughtco.com/history-of-duct-tape-4040012

https://tapeuniversity.com/products/foil-tapes/ul181ap-ul181bfx/

https://pstc.org/wp-content/uploads/2021/05/Krupa_David.pdf

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