The hood is found directly above the cooking surfaces in any kitchen and is the beginning of every kitchen exhaust system. The hood is where the grease vapors, heat, and exhaust are captured, filtered, and ventilated.
Pictured below is a large Island Canopy kitchen hood.
There are many different makes and models of hoods, but they all have the same purpose, covering the cooking surfaces properly to capture all the exhaust air.
Anatomy of the Hood
As exhaust from the cookline contaminated with grease begins to move through the KITCHEN EXHAUST SYSTEM, a large amount of grease can be captured in the hood by grease removal devices. These devices are commonly:
- Grease Filters
- Grease Drip Tray
- Grease Cup
- Plenum (not shown here – defined as area behind the filters)
The picture below (Figure 18) is a simple makeup of a hood, however. This picture is an example of a wall-mounted canopy hood. We will be using this hood throughout this training manual to describe the cleaning process.
Grease Filters of multiple designs are in every hood. As the air travels through the filters, the aerosolized grease will attach itself to the filters. This process removes most of the grease from the air before it travels through the rest of the KITCHEN EXHAUST SYSTEM (ductwork and exhaust fan).
The liquid grease that is captured in the filters will drain down into the Grease Drip Tray. This tray is angled so that the grease will continue to drain into a dedicated Grease Cup.
The Grease Cup is designed to be easily removed and emptied by the kitchen staff in between Bare Metal Standard services and as often as required.
Hood Styles
There are many different styles of exhaust hoods. These styles will vary based on a few factors:
- Location of the hood in the kitchen:
- Against a wall (Figure 19)
- In the middle of the room.
- Manufacturer of hood (see Reference Material for specifics on hood manufacturers)
- Captive Aire
- Halton
- Greenheck
- Gaylord
- Cooking equipment
- Some hoods are designed for the exact cooking equipment they cover.
- Location limitation (hood installed in existing building)
The hood type will end up affecting the manner of preparation needed for the Bare Metal Standard service process. It is important to become familiar with the obstacles that come along with each hood type.
- Wall Canopy Hoods
- Single and Double Island Hoods
- Backshelf Hoods (Pass-over style)
- Eyebrow-Type Hoods
- Self-Cleaning Hoods
- Ultraviolet Hoods
The above image (Figure 20) is a snapshot from the NFPA 96 book FIGURE A..3.3.33 Styles of Hoods.
Wall Canopy Hoods
Wall Canopy Hoods fit their description quite plainly as the back side of the hood rests against the wall, as seen in the image below.
Island Hoods
Island Canopy Hoods also fits is description well as it is a hood that is isolated in the middle of a room or kitchen with no sides of the hood against a wall. These hoods come as Single Island Canopy and Double Island Canopy hoods. Figure 22 is an example of a Double Island hood installed against each other. If you look carefully, you can see the seam in the side of the hood highlighted with a yellow line.
Backshelf Hoods
Backshelf hoods are low proximity hoods that hang lower over the cooking equipment. This means that they need less air flow to still capture the exhaust and grease produced by the cooking equipment. Designed to be a smaller hood than traditional Wall Canopy Styles to fit in smaller kitchens and lower ceilings. (Figure 23 – A burger restaurant with Backshelf Hood).
Eyebrow-Type Hoods
These systems are rather specific to bakery exhaust. They are used as hood on the exterior of the roll-in oven that is used in grocery stores and other high production bakery locations (typically institutional work). (Figure 24).
Self-Cleaning Hoods
These systems are very expensive and rarely properly maintained by the end user (restaurant owner or facility maintenance). The overall construction of the hood is similar to standard canopy hoods; however, the inner workings have a few specific differences:
- The interior of the hood is designed to collect grease in specific locations (Figure 25).
- Water spray nozzles inside the hood directed at the grease accumulation sites (Figure 26).
- Chem pump to inject a surfactant (degreaser) into the system
- Interior Drain inside the hood
- Rather than having a hood drip tray and grease cup, these systems clean themselves out.
Water wash system look like they could be a wonderful solution to the fire hazard that the grease buildup presents in these systems, which is only the case when they are properly maintained.
If not properly maintained, these systems trap grease on the interior of the hood and will continue to collect in an area that is out of sight, therefore, they are frequently left underserviced.
This has often resulted in plugged interior hood drains that cause water overflows when the water wash system is activated.
Ultraviolet Hoods
These systems are rarely used but do exist in the market. There was period of time when a specific company, Halton, was marketing the use of UV light to vaporize grease particles and eliminating fire hazard that grease deposits present in kitchen exhaust systems (Figure 27).
The result was that the special UV bulbs did vaporize or “dry out” the grease particle, but only in very low volume. For low grease production the style of these hoods worked, but for grills, fryers, and broiler systems, grease was gathering on the light bulbs themselves causing the system to be ineffective at vaporizing grease particles.
The Hood – NFPA 96 Codes
NFPA 96, Chapter 5 Hoods and Chapter 6 Grease Removal Devices in Hoods is where we can find codes that cover the specifics on hood construction. See NFPA 96 for codes that are specific to the kitchen exhaust system.
The construction of the KITCHEN EXHAUST SYSTEM hood and the styles discussed above are approved by NFPA 96, however, no specific codes are necessary to mention here to properly provide service.