Type I hoods come in numerous styles and various categories. All model codes use the Type I and Type II terms. A Type II hood is not meant for grease removal and is only used to remove steam, vapor or heat. Type II hoods typically do not include a fire suppression system unless the ductwork merges with a Type I duct system. When in doubt, contact your local AHJ for their approval as to use and fire suppression requirements. Never specify a Type II hood when grease will be present. You may however, use a Type I hood in lieu of a Type II hood.

Type I hoods include listed grease filters and fire suppression equipment. Baffles or extractors may replace filters when tested and listed for such use by a certification agency.

We talked about the advantages of a listed hood vs. a non-listed version in our November Newsletter. We will concentrate on listed hoods here. To obtain a listing, manufacturers must submit hood models for evaluation by UL to meet Standard 710, the “Standard for Safety for Exhaust Hoods for Commercial Cooking Equipment”.

BASIC CATEGORIES

There are two basic categories spelled out in UL 710, hoods with dampers and those without dampers. When a model with a fire actuated damper is selected, the damper is usually located at the exhaust duct opening and closes when fire is detected. This action prevents flames from entering the duct system and traveling up to the roof. If the hood has an internal duct opening for makeup air, it will normally include a damper as well. Fire actuated dampers when used, are an integral part of a listed device. If you have any questions about what is acceptable, refer to the local building department or fire inspectors for applicable codes in the project area when making a decision.

Listed exhaust hoods with fire-actuated water systems are typically water-wash hoods in which the wash system also operates as a fire extinguishing system. In addition to meeting UL 710, hoods are tested under UL 300, the “Standard for Safety For Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas”.

STYLES

Now for the various types or styles of Type I hoods. There are six versions and these are industry accepted ASHRAE descriptions:

Wall Mounted - Often referred to as a canopy hood
Single Island - Referred to as a canopy hood over a single line of equipment
Double Island - Same as above with back to back cooking lines
Backshelf - Only used for counter level equipment and has a lower profile
Eyebrow - Smaller configuration mounted to ovens and dishwashers
Pass-Over - Used with counter level equipment and used to serve plates over
to the serving side (May have exhaust ducts to side or employ a downdraft configuration.)
Recirulating - Cleans grease laden air within itself, releasing air back within the building space. (See explanation below).
Ultraviolet - Refers to the UV light system and can fit into several of the hood categories above. (See explanation below).

ACGIH or the American Conference of Governmental Industrial Hygienists in their 2001 edition titled Industrial Ventilation use different terms to describe hood types. These terms are not generally used by kitchen equipment professionals but may be used by some environmental health departments. We list them here in the event you encounter one of these terms:

HAW - Hood against wall
ITH - Island type hood
LSW - Low side wall

Reciruclating hoods exist in their own separate category. The recirculating system is listed under UL Subject 710B. This type of hood may also be referred to as a ductless hood since there is no duct to the roof. Ducts may extend to another room or area for discharge of the cleaned air. Also refer to NFPA 96, Chapter 10. Recirulating hoods are for use only with electric equipment. Recirculating hoods are not for use with gas fired or solid fuel equipment. Capacities are limited. Designers should work with factory representatives to determine effective capacities for given situations.

Ultraviolet hoods refer to the ultraviolet light system generally located directly behind the listed filters. Ultraviolet light chemically reacts with grease particles suspended in the air stream and changes the chemical composition from grease molecules to carbon dioxide and a limited amount of water vapor. The ultraviolet light is able to extract small particles under 2 microns, something most filters have difficulty with. More of these systems are being installed recently with the frequency of duct cleaning being reduced. While numerous systems are installed in the United States and Canada, the area around Vancouver, BC has seen many of these successfully installed within the last few years. Note that ultraviolet light may also be part of pollution control devices downstream of the exhaust fan.

BENEFITS

Remember that a listed hood can save an owner thousands of dollars over the life of a system by operating with less exhaust and make up air than an unlisted device. Choosing a hood is more than picking the least expensive hood that fits over a given cooking lineup. It deserves consideration in terms of choosing a model that fits the need of the cooking lineup, proper overhangs and air flow requirements. It is the amount of airflow required that will impact the cost to an owner over the lifetime of the installation.

ASHRAE HANDBOOK

The most informative resource for all designers is the 2003 ASHRAE HANDBOOK, Chapter 31, titled Kitchen Ventilation. You can order this handbook directly from UP YOUR STACK™ by sending us an email at info@upyourstack.com. Our on-line store will be open in early 2005. Watch for the announcement.

The December 2004 Journal of Environmental Health features an article titled Kitchen Hood Performance in Food Service Operations. The study examined hood flow rates in 60 restaurants and a total of 89 hoods. Only 24 percent met ASHRAE guidelines for adequate air flow. This study also deals with cleanliness and sanitarians’ inspection reports. A link was not available at the time of this newsletter release.

Ref: 2003 ASHRAE Handbook