The U.S. Patent and Trademarks Office issued a patent toGreenheckin October 2004 for a two-stage air purification system its engineers invented for installation and operation within a kitchen ventilation hood. The Grease Grabber™ (GG) multi-stage filtration system is available in Greenheck kitchen hoods and uses the Greenheck Grease-X-Tractor™ (GX) filter along with a secondary filter to remove 80% of the grease from the airstream.