A commercial kitchen hood system uses fans, ducts and filters to capture heat, grease and other contaminates in the air. The exhaust usually passes through a cleaning system before exiting the building. A commercial hood system also brings in make-up air to replace the air lost through the ventilation process. According to the National Institute of Building Sciences, hoods fall into two categories: type I and type II. Type I hoods handle grease and include several integrated components; type II hoods handle steam, vapor, heat and odors, but not grease.
Identify the exhaust hood. Most commercial kitchen hoods are in the form of a large box with an open bottom that sits on top of the fryers and burners. The smoke rises up through the hood and into the exhaust ducts before escaping outside.
Note the location of the fans. Commercial kitchens may have two fans: one for the exhaust air and the other for the make-up air. The fan for bringing in the make-up air could be an independent system, or might be connected to the building's heating, ventilation and air-conditioning system. You could install an exhaust fan on the roof directly on top of the exhaust duct system. Also known as an up-blast fan, this system consists of a motor, fan blades, vents to cool the motor and a drive shaft to connect the motor to the blades.
Locate the ducts. There should be one duct assembly for the exhaust air and one for the make-up air. Ducts are normally made of steel. Non-combustible elbows, hangers and other components connect the ducts to the hood, through the interior building walls and out to the exterior of the building. Ducts often reside within fire-rated shaft enclosures made of gypsum board, plaster, concrete or ceramic tiles.
Identify other components, such as back-splashes, vapor-proof lights, grease filters and cups. Stainless steel back-splashes protect the kitchen wall from grease splatters and water splashes. Vapor-proof lights function in wet and greasy areas. Grease accumulates in the grease filters and drains into the grease cups.
According to an information sheet on the BPA Air Quality Solutions website, an air purification system supplier, comprehensive kitchen exhaust systems also include outdoor or indoor cleaning units to keep the indoor air clean. This also reduces maintenance costs because grease and other exhaust residue build-up could damage the ducts, clog up the fans and stick to the walls.