You are more than excused for being confused about duct tape usage. It’s called duct tape, so assuming that you can use it on ducts is logical.
However, it turns out that the name is horribly misleading. To make matters even more confusing, there actually is duct tape; it’s just not called duct tape.
Duct tape cannot be used on dryer ducts because it is not UL 181A-compliant. Duct tape does not adhere well to HVAC systems and can become a fire hazard when it dries out.
Regular Duct Tape Cannot Be Used
The International Residential Code (IRC) is a set of building requirements that is used worldwide to set a standard of building safety.
The IRC has specific requirements for the installation and sealing of ducts, and, despite the misleading name, duct tape is not a material that can be used on ducts according to these requirements.
Section M1502 of the IRC covers dryer exhaust venting, including duct construction. Section M1502.4.2 says that ducts have to be sealed in accordance with Section M1601.4.1.
Section M1601.4.1 says:
“Tapes and mastics used to seal fibrous glass ductwork shall be listed and labeled in accordance with UL 181A and shall be marked “181A-P” for pressure-sensitive tape, “181A-M” for mastic or “181-H” for heat-sensitive tape.”
UL 181A tape is specially designed for use on HVAC systems. It has been tested to ensure proper adhesion to ductwork and to limit fire hazards.
Before a tape can be classified as UL 181A compliant, the tape is tested on its:
- Fire resistance
- Pressure resistance
- Performance in high/low temperatures
- Mold growth in humid conditions
Also, remember to check your local building codes for more specific regulations. The IRC is used as a template, but local building codes may add on additional requirements.
Problems With Using Duct Tape on Dryer Ducts
Duct tape is not a UL 181A-compliant tape. It fails to meet the necessary safety requirements to be used on dryer ducts.
Duct tape is a cloth-backed tape with rubber adhesive. Although this tape is very strong, it is far from the ideal choice for dryer ducts.
Dryer ducts carry the hot air produced by the dryer. When the dryer is not operating, the ducts are at more moderate temperatures. In addition, they lead outside, which makes them partially subject to outside temperatures.
All of this means that the dryer ducts can experience a large temperature fluctuation throughout any given day and throughout the year.
In an experiment conducted by a lab in Berkeley, CA, they found that the adhesive on duct tape was degraded by the temperature fluctuations and failed to remain attached to the ductwork.
This is hardly going to be a solution to your problem!
The cloth that duct tape contains also poses a risk to inhabitants if it is used on a dryer duct. If the duct tape adhesive dries out, the cloth becomes a highly flammable material.
These two characteristics of duct tape make it ineffective in almost all of the requirements for UL 181A-compliant tape.
- It is a fire hazard.
- It performs poorly in varying temperatures and thus falls off ventilation.
- Falling off ventilation leads to the chance of leakage around the duct tape.
- It has poor pressure resistance as the tape adhesive is degraded because any pressure will cause the compromised seal to break.
Perhaps a quote from Max Sherman, the head of the Energy Performance of Buildings Group in the Berkeley lab, can dispel any final doubts of the inefficacy of duct tape for this use:
“We tried as many different kinds of duct sealants as we could get our hands on. Of all the things we tested, only duct tape failed. It failed reliably and often quite catastrophically,”
UL 181A-Listed HVAC Tape Must Be Used
UL 181A-listed HVAC tape must be used for dryer vents, as per IRC safety regulations. Tapes categorized as UL 181A are specially created for use on HVAC systems.
They must be made of either aluminum or an aluminum alloy foil, and they must be at least 2.5″ (6.35 cm) in width.
The aluminum material of these tapes allows them to properly adjust to temperature changes because the metal will expand and contract with the duct.
A width of at least 2.5″ ensures that the tape is wide enough to cover the seam with enough extra tape on each side to create a strong seal.
UL 181A-listed tapes are classified as having a Flame Spread Index (FSI) of less than 25. An FSI of less than 25 puts UL 181A tapes in the Grade A category (0-25 FSI), meaning they do not burn easily or quickly.
These tapes must also have a Smoke Developed Index (SDI) of less than 50. The SDI measures how much smoke is produced as an object burns. At less than 50 SDI, UL 181A-listed tapes do not produce excessive concentrations of smoke, even when ignited.
The FSI and SDI ratings are important because, without proper precautions, ducts can become highways for smoke and fire, carrying it throughout your home before you are even aware of it.
Most UL-181A-listed tapes include labeling on the actual tape. Look for aluminum foil tape with 181A-P printed on it.
Brands such as Shurtape, Nashua, StegoDIYTape, Uline, and Duck brand carry UL-181A-listed tapes.
Duck Tape Sells a Specialized Tape for Ducts
You may know the brand Duck Tape for its traditional duct tape products (and for the countless arguments caused among people—is it ducT tape or ducK tape?), but they also sell a UL 181A-compliant tape (amazon link).
Unlike their duct tape products that are made of rubber adhesive and cloth fibers, this product is a foil tape. It meets flame spread and smoke development requirements and has a large temperature range in which it can be used.
Make sure to purchase the correct tape for your dryer duct, as we have discussed in length above how using duct tape on HVAC systems is not safe.