A commercial hood is a ventilation system usually used in professional kitchens to expel fumes, vapors, or smoke created while cooking. Inside air is replaced with outside air, replenishing oxygen and diluting pollutants to keep the kitchen clean, healthy, and comfortable. Appropriate ventilation equipment can be as important in a kitchen as the cooking equipment itself.
Three main components make up a commercial hood ventilation system. The hood canopy collects vapors and fumes, while also protecting the kitchen and cabinetry from damage. The blowing system moves the collected fumes, and the ducting system allows them to be expelled and replaced by clean air.
The hood canopy is a piece made from stainless steel that collects cooking vapors. In professional kitchens, this piece is usually mounted to the wall. A hood cannot pull air in on its own; it simply holds fumes, vapors, or smoke to be moved by the blowing system. For that reason, a hood canopy must have ample "capture volume." It should extend at least 3 inches (7.6 cm) beyond cooking equipment on all sides, and should come to the front edge of the front burners.
The blowing system is what actually moves the air collected in the hood canopy. The force of a blowing system indicates how quickly the blower can move air. Often measured in cubic feet per minute (CFM), a commercial hood generally requires at least two blowing fans with a minimum force of 600 CFM (283 liters per second). Fans can be rotary, with traditional revolving blades, or centrifugal, with a barrel shape that has a higher capacity and operates more quickly. Many fans also have heat sensors that will active them, along with an automatic shut-off feature.
The fans generate the force to expel cooking vapors, which then move through a ducting system until they’re released outside. Ducts are made of smooth galvanized metal and should follow the shortest possible path to work efficiently. A straight path is also preferable, but if turns or bends are necessary, they should slope gradually to assist air flow. A commercial hood is ducted to the outdoors, and there should be no restrictions at the end of the duct.
Some commercial hoods work without ducting, instead relying upon replaceable filters. This is known as a non-vented or duct-free configuration. It simply filters existing air and recycles it back into the kitchen, rather than replacing it with fresh air. Most hoods also feature a carbon filter kit. The filter should be replaced regularly for maximum efficiency.