Duct Tape is well-known as a versatile, somewhat sketchy, repair solution. But those in the HVAC field know that despite the name, Duct Tape isn’t the best choice to seal ducts. Most people go so far as to say the tape absolutely shouldn’t be used for sealing ducts. And since it could violate building codes in certain areas, we tend to agree. And with that, we have one of the greatest naming ironies of all time. But if the tape wasn’t made to be used on ducts, where did the name Duct Tape come from? Or, should we really be saying Duck Tape instead of Duct Tape? These are good questions with no definitive answers.
Not for Ducts, so Why the Name?
The details of the tape’s origin story are somewhat disputed, but some of the broad strokes are agreed upon. Most sources say that the name came from the cotton duck material form which the tape was made. According to popular lore, Duck Tape was made for the United States Army by the Permacel division of the Johnson & Johnson company to keep moisture from getting inside ammunition cases in the field. A deeper look into the tape’s creation suggests that the idea was conceived of by a woman in Illinois, who had two sons fighting in World War II. The woman, named Vesta Stoudt, worked for Johnson & Johnson where her job was to seal boxes of ammunition with paper tape. Once sealed, the boxes were dipped in wax to protect their contents from moisture. Unfortunately, that process didn’t help the durability of the tape. Stoudt was worried because the paper tabs left for opening the boxes, were prone to ripping, which made the boxes difficult to open. The extra time it took to open an ammunition box could mean the difference between life in death in the trenches. Stoudt imagined a better method for sealing the boxes with strips of durable duck material, so the tabs would remain intact to allow more reliable opening. When the idea was rejected by her supervisor, she wrote to President Franklin D. Roosevelt who liked the idea and passed it along to high ranking military officials and eventually the tape was put into production.
If this story is true, the name Duck Tape seems more correct than Duct Tape. There may be more than one way to spell the tape in question, but there even more ways to properly seal ducts.
The Correct Way to Seal a Duct
Foil-backed tape is a great choice for heating ducts. Unlike duct tape, this tape contains acrylic or butyl adhesive to resist drying out and becoming brittle. The metal foil backing also holds up to temperature changes without shrinking and failing. With foil-backed tape, excellent duct sealing is possible without the messiness of mastic.
Duct mastic is a gooey substance used to fill gaps and stop leaks. It is applied with a brush or putty knife. For best results, larger gaps in joints should be covered with fiberglass mesh tape adding a layer of mastic.
Injected aerosol sealant is a sticky vinyl polymer that was developed at Berkeley Lab’s Environmental Energy Technologies Division. When pumped through the ducts, it automatically seeks out leaks, spans the hole, and dries, to permanently seal leaks. The Berkeley lab tested this sealant every 20 minutes for two years, with no noticeable change in duct tightness.
UL Listed HVAC Tape
In some HVAC applications, UL listed materials are critical for code compliance. Following the codes ensures that the HVAC tape used has the proper adhesion and shear strength needed to stay in place for the life of the HVAC system. To receive a UL 181 listing, tape used to seal air duct and air connectors is subjected to several tests to determine how it will perform under the following conditions: Flame Resistance, Mold Growth & Humidity, Temperature, Static Load, Impact, Pressure, Collapse, Tension, Torsion and Leakage Test. These performance tests determine whether a tape will receive a UL listing. The two UL designations for HVAC tape are UL 181A-P(PDF) and UL 181B-FX.
UL 181A-P is the standard for HVAC tape used to seam, seal and join rigid duct work. This listing has stringent testing requirements that must be met. Additionally, the tape must be made of aluminum or aluminum alloy foil and be at least 2.5"W. This tape must also include a release liner.
UL 181B-FX is the standard for HVAC tape used to seam, seal and join Class 1 Flex Duct. Products that fall under this designation can be made from a variety of materials such as foil, film or cloth, but must be at least 1.825"W.
Benefits of Sealing Ducts
In a typical building, about 20 to 30% of the air that moves through the duct system is lost due to leakage through holes, and poorly connected ducts. This leakage makes it difficult to keep indoor spaces comfortable no matter how high the thermostat is set, which ultimately results in higher utility bills.
Sealing ductwork will provide two major benefits:
Lower heating and cooling costs/ utility bills
Better coverage to rooms that are difficult to heat and/or cool
In short, a duct system that is properly sealed can make any building more comfortable, energy efficient, and safer. It can also save you money! First Supply is your trusted HVAC supply store – find everything you need for your next project.