UL 900: Safety Requirements for Air Filter Units

Intertek has applied decades of flammability testing experience with building materials for UL 900 testing. For the first time, filter manufacturers have a choice in independent testing partners for the UL 900 standard.

Filters found in compliance with the UL 900 test method are eligible to bear an ETL mark with a “Classified to UL 900” designation. This mark tells buyers that the product has undergone testing by an independent testing laboratory and has met applicable requirements. Intertek's ETL Mark is backed by responsive customer service and is recognized throughout North America by Authorities Having Jurisdiction.

Sample UL 900 Testing Process:

The UL 900 standard is designed to determine combustibility and the amount of smoke generated for air filter units of both washable and throwaway types used for removal of dust and other airborne particles from air circulated mechanically in equipment and systems installed in accordance with the Standards for Installation of Air Conditioning and Ventilating Systems, NFPA 90A (Other Than Residence Type), Installation of Warm Air Heating and Air Conditioning Systems, NFPA 90B (Residence Type), the International Mechanical Code, the International Fire Code, and the Uniform Mechanical Code. These requirements also cover media intended for assembly into air filter units. The UL 900 test method simulates a fire within a duct, which impinges on the filter.

Since the smoke generation of an air filter unit, as well as its combustibility, depends upon the nature and quantity of the material collected by the filter, the test requirements of this standard, for classification purposes, apply only to air filter units in a clean condition. Consequently, when filters are susceptible to the accumulation of combustible deposits, it is intended that maintenance and inspection practices should be followed as proposed in Appendix B of NFPA 90A.

  • The test filter is mounted inside a standard size duct and a specific air flow through the filter is established.
  • Upon the start of the test, a methane flame is ignited on the upwind side of the filter, resulting in a direct flame against the filter, which is maintained for three minutes.
  • For classification, strict limits are placed on the amount of smoke and flames that may pass through the filter.
  • For Class I, no flames or sparks may pass through the filter and only a small amount of smoke can be generated.
  • For Class II, limited flaming and sparking are acceptable and a larger amount of smoke may be generated.

Intertek UL 900 Solutions

For nearly 50 years, Intertek has been a leader in HVAC/R testing. Manufacturers trust our experienced testing and accurate results. Our engineers and staff participate in standards writing committees and industry associations, providing the insight and expertise clients need in meeting market requirements.

Manufacturers rely on Intertek to determine any number of ratings, including energy consumption (including SEER ratings), product durability and reliability, acoustics and air flow, just to name a few. We are one of the few testing facilities in the world devoted to testing to the ASHRAE 52.2 and UL 900 standards.

Intertek is an independent testing organization for the Air-Conditioning, Heating and Refrigeration Institute (AHRI), and an administrator and official performance test lab under the Gas Appliance Manufacturers Association (GAMA) Certification Program.


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