Clearance: A minimal 450mm clearance is recommended from the cooking floor towards the underside of any grease filter. The TR19 certification to awarded to firms as evidence that commercial kitchen extraction and ventilation systems have been cleaned, degreased and preserved to the required common. UL 2221 - beneath this listing, https://commercialkitchenextracts23344.blogscribble.com/37040299/the-fact-about-grease-tight-extract-ductwork-that-no-one-is-suggesting