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A UL 181 Class 0 air duct is a type of air duct that has a Flame Spread Value of zero and a Smoke Developed Index of zero when tested to the UL 723 standard (ASTM E84). This means it has superior fire safety characteristics, as it does not contribute to the spread of flame or smoke. This makes them the highest-rated class for flexible air ducts, suitable for a wide range of HVAC applications where fire safety is critical, such as general supply, return, and exhaust systems.
Key characteristics and testing
- Zero flame spread and smoke development: The defining characteristic of a Class 0 duct is its performance on the UL 723 (or ASTM E-84) test, which measures a material’s contribution to fire.
- UL 181 standard: Class 0 is a classification within the UL 181 standard, which is the test method for evaluating the performance of flexible air ducts and connectors.
- Higher rating: This is the highest rating a flexible air duct can receive, surpassing Class 1, which allows for a flame spread index of up to 25 and a smoke-developed index of up to 50.
- Material: Class 0 ducts are often made from highly resistant and non-combustible materials, such as aluminum alloy.
Applications
- General HVAC: They are suitable for general HVAC supply, return, and exhaust systems in buildings.
- Versatility: Their versatility allows for use in both high and low-velocity air-conditioning and ventilation systems.
- Specific installations: They are a good choice for installations where building codes require high fire safety standards for ductwork, such as in multi-story buildings.