Types of Kitchen Hoods
Two different types of kitchen hoods are used in the commercial kitchen. These hoods are classified as a TYPE I or TYPE II ventilation hood.
TYPE I hoods are used over cooking equipment producing heat and grease laden effluent. These hoods require a fully-welded ducting system.
TYPE II hoods are used over non-grease producing cooking equipment exhausting heat and condensation.
Various categories of TYPE I and TYPE II ventilation hoods exist for different applications and personal preferences.
TYPE I Hoods:
The canopy hood uses the updraft concept to capture and contain the contaminated air generated by the cooking process. Heated air is less dense than the surrounding air causing it to become buoyant. If no cross drafts are present, the contaminated air will rise up into the hood where it is captured and contained until it can be exhausted through the grease filters to the outside. Wall, single island, and double island represent the three configurations of canopy hoods. Although each configuration is mounted from the ceiling directly above the cooking equipment, each is used for a different application.
Wall Canopy Hoods:
The wall canopy hood is used when the cooking equipment is placed against a wall. Hoods that are used against a wall have a tendency to capture and contain the effluent using less airflow than in an island type application. Make-up air from the kitchen enters the area below the hood replacing the air being exhausted. The wall located on the backside of the hood will cause the make-up air to enter at the front and sides of the hood creating a front-to-rear airflow pattern.
Single Island Hoods
A single island hood is used over one row of cooking equipment placed where no walls exist. Single island hoods can be seen from all directions, therefore, have four finished sides. With four exposed sides, this type of hood is more susceptible to cross drafts, spillage, and is dependent only on the thermal updraft of heat from the cooking equipment and how quickly the exhaust fan can rid the hood of contaminated air. These hoods should be sized larger and use more airflow than a wall canopy hood with the same cooking battery. The single island hood must overhang the cooking equipment by a minimum of 6 inches on all four sides of the hood. However, it is recommended that the overhang be extended to 12 inches on all sides of the hood. Extending hood overhangs increases capture volume which aids capture and containment. To eliminate the front to back airflow on a single island, a V-bank of filters improves capture and containment by directing the contaminated air to the center of the hood.
A wall canopy can be installed as an island hood with a finished back enhancing its aesthetic appearance. However, it is not recommended because the front to back airflow pattern of a wall canopy will cause capture problems when being utilized as a single island canopy.
Double Island Hoods:
A double island hood is placed over two rows of cooking equipment placed back to back. This configuration is made up of two wall canopy hoods placed back to back, thus creating four finished sides. This category of hood performs similar to the wall canopy hood due to two thermal plumes rising against each other, but is still susceptible to cross drafts. A double island hood must overhang the equipment by a minimum of 6 inches on all four sides of the hood but would benefit from additional overhang.
TYPE II Hoods:
TYPE II hoods are commonly referred to as oven or condensate hoods. In essence, these are stripped down exhaust only canopy hoods. The purpose of the TYPE II hood is to remove heat, moisture, and odor-ridden air from non-grease producing appliances. The hoods do not contain grease filter banks but rather a duct collar to exhaust the contaminated air. A TYPE II hood duct does not need to be fully-welded, instead it can be a standard galvanized duct because there is no grease loading. Flex-duct is not allowed for TYPE II hoods.
The oven hood is an exhaust only canopy hood with an exhaust duct collar for the removal of heat and vapor. These hoods are the simplest of all hoods and are usually placed over ovens or small appliances only producing heat and odor. For complete capture and containment, overhangs should be measured with the oven door open.
The condensate hood is an exhaust only canopy hood with U-shaped gutters to capture and direct condensate to a drain. It also has an exhaust duct collar for heat, moisture, and odor-ridden air to exit. Many manufacturers have options for condensate baffles in the hood to help condense the moisture laden air, one or two baffle configurations are typical, depending on the moisture content of the contaminated airstream. Condensate hoods are usually found mounted over dishwashers. For complete capture and containment of large plumes of heat and steam, 18-36 inches of overhang are recommended.