UL 181 Standard for Factory-Made Air Ducts and Air Connectors

The standard “UL 181 Standard for factory-made air ducts and air connectors” developed by Underwriters Laboratories (UL) describes the requirements for materials used in the manufacture of air duct and air connection systems to be used in accordance with the International Mechanical Code (IMC), International Residential Code (IRC) and Uniform Mechanical Code (UMC), National Fire Protection Association standards for the Installation of Air Conditioning and Ventilation Systems “NFPA 90a Standard for the Installation of Air Conditioning and Ventilation Systems” and “NFPA 90b Standard for the Installation of Hot Air Heating and Air Conditioning Systems”.

Ductwork and air fittings covered by these requirements include preformed lengths of flexible or rigid ductwork, sheet material for field fabrication of lengths of rigid ductwork, and preformed flexible air fittings.

For the purpose of these requirements, air ducts and air fittings are classified as follows:

Class 0 - Air ducts and air connection elements with zero surface combustion characteristics.
Class 1 - Air ducts and air connectors having a flame spread index not greater than 25 and a smoke development index not greater than 50 without evidence of progressive combustion.

In some HVAC (heating, ventilation and air conditioning) applications, UL listings are critical to code compliance. This means that the HVAC tape used has the proper adhesion and exceptional shear strength needed to effectively stay in place for the life of the HVAC system.

To achieve UL 181 listing, tapes used to seal air ducts and air connections are subjected to a series of tests including flame resistance, mold growth, and moisture, temperature, static load, impact, pressure, deflection, tension, torsion, and leak testing. These tests determine whether an HVAC tape can receive UL listing. Two commonly used in HVAC tapes include:

UL 181A-P is the standard for HVAC tapes used to bond, seal, and join rigid duct work or duct boards. This listing has more stringent testing requirements that must be passed to be approved and must be made of aluminum or aluminum alloy foil with a minimum width of 63,5 mm. These tapes must also be manufactured with a release liner.
UL 181B-FX is the standard for HVAC tapes used to bond and seal Class 1 flexible ducts. Products that meet this listing must have a minimum width of 46,4 mm and can be made from a variety of materials, including foil, film, or fabric.

Listed as a Class 181 air duct according to the UL 1 safety standard, tests include:

Testing of surface burning characteristics: This test measures how fast and how far a flame spreads in a Steiner tunnel. The values are calculated based on red oak, which has an arbitrary rating, and reinforced cement board, which has a rating of 0. The test is carried out in a 25-metre tunnel where pre-insulated panels (including the closure system) are put to the test.
Flame penetration test: This test measures the resistance to flame when the sample withstands a static load of 2 pounds per square inch. The test is performed in an oven for 30 minutes.
Burning test: This test measures the resistance to ignition and progressive combustion. A Bunsen burner is used during the test. The burner has pre-insulated duct sections mounted in horizontal, vertical and 45 degree positions.
Mold growth and humidity test: This test measures resistance to mold growth and the effects of high humidity. Samples are kept in an atmosphere saturated with water vapor for 60 days.
Low temperature and high temperature test: This test measures the resistance to high and low temperatures above normal service temperature.
Puncture test: This test measures the resistance to puncture by a piston. The test apparatus allows a piston to fall freely onto the surface of the channel sections.
Static load test: This test measures the resistance to sagging, permanent deformation or damage. Duct sections are placed horizontally on supports. The static load is applied to the longitudinal centre of the specimen by hanging two 24 kg weights from a 25,4 mm wide piece of pipe strapping material for 2,3 hours.
Impact test: This test measures the resistance to damage from an impact. The test apparatus allows a sandbag weighing 6,8 kg to fall freely onto the surface of the channel sections.
Erosion test: This test measures the resistance to erosion when air is passed through typical duct sections at two and a half times the manufacturer's rated speed.
Pressure and collapse tests: These tests measure resistance to positive and negative pressure. Duct sections are subjected to internal air pressures of 2 and a half times the manufacturer's nominal positive pressure and 2 and a half times the manufacturer's nominal negative pressure.
High temperature and humidity (as part of corrosion testing): This test measures the resistance of ductwork to damage and atmospheric corrosion. Duct sections are supported vertically in a closed chamber at a constant temperature of 90 degrees and 40 percent relative humidity for 100 days.
Corrosion resistance test: This test measures the corrosion resistance for iron and steel articles according to the standard “ASTM A90/A90M-09 Standard test method for weight (mass) of coating on iron and steel articles with zinc or zinc alloy coating”.
Leakage test: This test measures air leakage in ducts. Duct sections, including joints, are subjected to an air pressure of 1 Pa at a water column of 12,7 mm maintained for a period of 124,5 hour. The amount of leakage is the total air volume recorded from the time the test pressure is established in the sample.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "UL 181 Standard for Factory-Made Air Ducts and Air Connectors" standard are also provided to businesses.