The Right Test Standard For Pollution Control Units (KVS/001-0217)

February 16th, 2016

The following information is intended as a guide to understanding pollution control units and the importance of why UL 1978 Standard for Grease Ducts should be used when specifying a pollution control unit. Read on to learn more.

The engineers and food service consultants who select and specify kitchen systems carry a great deal of responsibility. That’s why it’s important to specify certified products designed for optimal performance, reliability and safety.

About Pollution Control Units

Pollution Control Units (PCU), also known as Air Purification Units or Exhaust Filtration Systems, have been in use in commercial kitchen exhaust systems for many years. However, due to new requirements of many municipalities and local Authorities Having Jurisdiction (AHJ), they are quickly becoming an increasingly integral part of commercial kitchen exhaust systems. Using PCUs help reduce the release of grease particulate and odor from cooking operations into the
surrounding space and atmosphere. They are useful in multi-purpose buildings where the kitchen exhaust can be routed horizontally through a side wall near street level rather than needing to install long runs of vertical ductwork to reach a rooftop exhaust fan. In addition, eliminating grease and odor from the exhaust air is desirable to the occupants of nearby buildings as it prevents the buildup of grease on roofs, walls, sidewalks, and cars.

A PCU serves three main purposes. Its first purpose is to exhaust grease laden air from the commercial kitchen space through a Type I kitchen hood. Initial filtration of the grease laden air ideally occurs at the kitchen hood. The PCU is connected to the kitchen hood by a fully-welded or listed grease duct running from the hood to the PCU. The air is pulled through the duct and PCU by an exhaust fan at the PCU outlet. Secondly, as the air is pulled through the PCU, multiple stages of increasingly efficient filtration remove grease particulate from the exhaust airstream.

Lastly, the air passes through a media that neutralizes the cooking odor.  

PCUs as They Relate to Codes and Standards

The International Mechanical Code (IMC) requires that a Type I hood be used where the appliances produce grease or smoke. The hood is then connected to the duct by liquid-tight welded or brazed joints. The duct run from the hood collar to the exhaust fan is also to be constructed such that all joints and seams are of a continuous liquid-tight weld or braze, unless the duct is a factory-built grease duct that is listed in accordance with UL 1978 – Standard for Grease Ducts. It then follows that if grease laden air is to be exhausted through a PCU to an exhaust fan, that the PCU should actually be part of the grease duct. As Pollution Control Unit 2 Kitchen Application KVS/001-17 Greenheck Product Application Guide such, PCUs should also be required to have fully welded or brazed joints, or be listed in accordance with UL 1978.

UL vs. ETL - Evaluation and Listing of PCUs

When PCUs were first developed, there was not a specific standard to which the products could be evaluated (and at
the time of this writing there still is not a standard for PCUs). This leaves the determination of what tests are required for listing to independent third parties such as UL and ETL.

Underwriters’ Laboratories viewed PCUs as a grease duct and determined that evaluating PCUs to the heat related tests from UL 1978 – Standard for Grease Ducts were the proper tests to obtain an UL Listing for PCUs. (Page 3)

ETL determined that evaluating PCUs to the heat related tests from UL 710 - Standard for Exhaust Hoods for Commercial Cooking Equipment, listed of page 3, were adequate to obtain an ETL Listing for PCUs.

There are stark differences between the tests required to obtain listings to each of the standards. Reviewing the comparison on page 3, it becomes apparent that the tests for UL 1978 are more rigorous and better suited to evaluate grease duct, whereas UL 710 was developed for listing exhaust hoods. Grease duct is to function as an air tight and liquid tight conduit for grease laden kitchen exhaust air. As such, it should have sound structural integrity, prevent the leakage
of any grease or smoke to the exterior of the duct, as well as contain any fire within the duct, even when subjected to the extreme temperatures associated with grease fires.


Knowing that PCUs are, in fact, an extension of the grease duct, it follows that UL 1978 is clearly the correct standard to use for the safety evaluation of PCUs.

There are several manufacturers of PCUs. The specifications for most PCU manufacturers state that the unit is listed to UL 710 – Standard for Exhaust Hoods for Commercial Cooking Equipment. Only a few manufacturers specify that their PCUs are listed to UL 1978 – Standard for Grease Ducts. Based on the increased rigor of UL 1978 for fire safety, we recommend that all PCUs be tested and evaluated to UL 1978. Specify with confidence, choose a UL 1978 PCU.

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