23 28 13: Commercial - Kitchen Hoods
Last updated: 06-03-2009
The science of commercial kitchen ventilation includes both exhausting air as well as providing replacement air within the cooking area. Whether a restaurant is a small free-standing site or a large institutional kitchen, managing and balancing airflow is a complex issue. It is a challenge to properly ventilate commercial kitchens, as they require moving large volumes of air through ductwork and equipment placement in very restricted spaces.
Overall design, construction, installation coordination, and maintenance are required to get optimum performance and an energy-efficient air balance from the system.
SMACNA, through its technical manuals, provides the information and drawings to illustrate the elements of construction and installation of commercial kitchen ventilation systems. The information is intended to encourage standardization in installations and to call attention to the appropriate segregation of responsibilities of those involved with food service design and installation.
A Typical System
A typical kitchen ventilation system includes an exhaust hood or canopy, ductwork, fan system, and a means of providing adequate make-up air. The entire system must constitute a fire-safe assembly within the building.
Exhaust hoods and canopies capture heat and contaminates in the air by means of filters, extraction baffles (cartridges), and water mist systems. There are many style variations of hoods with canopy styles—a large box with and open bottom—being the most common. Styles selection is based on the type of oven and the expected contaminates to be removed. While there are several styles of hoods, all fall within two major categories:
- Type I hoods carry a listing label and are manufactured and installed according to the manufacturer's and listing agencies' requirements. They are designed to handle grease and include a number of integrated components within the hood.
- Type II hoods are used in the collection of steam, vapor, heat, and odors—but not grease. The two sub-classifications of Type II hoods are condensate and heat/fume.
Backshelf hood over cookline
Exhaust ductwork provides the means to transfer contaminated air, cooking heat, and grease vapors from the hood to the fan.
- Ducts accumulate combustible grease and should be constructed from 16- steel or 18-gage stainless steel as per code requirements.
- The ducts must me securely supported by non-combustible duct bracing and supports designed to carry the gravity and seismic loads as per code requirements, no fasteners should penetrate the duct.
- The duct is often run inside a shaft enclosure and that enclosure is typically constructed of gypsum board, plaster, concrete, or ceramic tiles and must be an approved continuous fire-rated enclosure.
Hood and ceiling enclosures
Exhaust fans move the heat and contaminated air out of the building. All exhaust fan components must be accessible or have removable access panels for cleaning and inspection and must be designed to contain and drain any excess grease. There are three major types of exhaust fans:
- Up-blast fans are typically aluminum centrifugals that are designed for roof mounting directly on top of the exhaust stack.
- Utility fans are normally roof-mounted with the inlet and outlet 90 degrees from each other and are typically used where high-static pressure losses exist.
- Inline fans are typically located in the interior duct and are used where exterior fan mounting is impractical.
Up-blast fan assembly
In order for the exhaust system to work properly, make-up air is required to replace air equal to the amount removed. Make-up air can be provided via an independent system or in combination with the building's HVAC system.
Kitchen Ventilation Concepts
To better understand why a kitchen ventilation system needs to be designed and constructed in a very specific manner, the principles behind air movement must be understood. Buildings are required to adhere to indoor air quality regulations and, depending upon the jurisdiction, sometimes exhaust air quality regulations. The food service industry must meet higher air quality regulations than standard building exhausts due to the type of contaminated air produced by cooking food.
Exhaust air is the starting point in restaurant kitchen ventilation design. Exhaust air is the air that is contaminated by smoke and grease-laden vapor (aerosols) created by the cooking source. This air must be removed from the building in a manner that complies with local codes and ordinances.
Make-up or, supply air must be provided in approximately equal amounts to replace the kitchen air being exhausted. Typically, outside air is supplied through a designed make-up air system. Most health codes require that an amount of fresh outside air be included in any replacement air calculation to assist in indoor air quality requirements.
The Kitchen Ventilation Team
The safety and design requirements of both commercial kitchen exhaust and make-up air systems require that a group of key players have sufficient knowledge of the subject to coordinate the entire process from design to operation. The following overview provides a brief description of each team member with a vested interest in the process and suggests criteria necessary to design and install a comprehensive and balanced system that offers efficient operating costs, climatic controls, and satisfies building and fire regulations.
An owner/facility manager needs to understand the interdependence of each piece of the kitchen system to recognize the value of having a complete and properly integrated system that will provide a productive and comfortable work environment that is also cost-effective.
The architect is responsible for the commercial restaurant's design including fire-resistive walls, floor-to-ceiling assemblies, roof-ceiling assemblies, and the protection of openings as well as the horizontal and vertical smoke barriers. In consideration for fire protection, the architects first must determine the overall function of the structure and the type of occupancy of its spaces. The architect is also responsible to design appropriate spaces within the building that are required to be separated by fire-resistive assemblies with protected openings, as set forth in the local building code. The architect will communicate and cooperate with the authority having jurisdiction at the building site and comply with any special conditions of fire protection design required by that authority.
Contractors must have access to and be able to use manuals and design procedures in order to fully comply with design objectives and specifications established by the kitchen ventilation system designer. SMACNA's Kitchen Ventilation Systems & Food Service Equipment Guidelines documents industry-accepted practices for the fabrication and installation of food service-related equipment.
Local code authorities must be capable of judging adequacy and comparability in the installation of commercial kitchen ventilation systems and its components and assemblies. The most critical aspects of a code official's job are fire and safety issues. However, understanding the "standards of practice" that quality contractors strive to achieve is also important.
The engineer or system designer is responsible for knowing where ducts, pipes, and other conduits pass through required fire-rated separations or smoke barriers. Duct penetrations must be shown on the mechanical plans and designed with an appropriate protection method. Use of standard symbols is highly recommended. International Mechanical Code (IMC) and the National Fire Protection Association Standard # 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA #96), NFPA 17A and 90A, all state that the designer must show on the plans the location and mounting details of all automatic fire doors, dampers, access panels, and other fire protection means incorporated into both the exhaust and supply systems.
To coordinate all requirements, designers must possess all necessary information on barrier locations, occupancy assignments, protection planning, rating, and identification of compartments and structural components. Drawings must show fire and smoke dampers and heat stops. The engineer/designer should specify the hourly rating and type of damper and requirements for access doors. Specific framing requirements of openings should be provided in the architectural and structural drawings submitted for building permits. Thickness and type of fire resistive material may vary by jurisdiction. There should be coordination in advance with local authorities to verify the acceptance of the methods and equipment proposed for use.
Relevant Codes and Standards
Local codes are generally adopted from either the International Mechanical Code (IMC) or the National Fire Protection Association Standard # 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA #96) or a combination of the two with particular local issues of concern included. In many major cities, local codes are written and published by local building officials; however, such codes are frequently based on one of the national codes previously mentioned.
Certain government agencies such as the General Services Administration (GSA), the Department of Health and Human Services (HHS), Housing and Urban Development (HUD), and the U.S. Army Corps of Engineers have specific standards or codes that must be accommodated in construction performed for these agencies.
In some instances, the insurance companies that underwrite the building have recommendations or standards from the American Insurance Association (AIA).
Planners and designers need to identify and consult the local authority having jurisdiction and local governing codes prior to designing a kitchen ventilation system. Consideration must be given to both the building and fire codes.
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)—ASHRAE seeks to advance the arts and sciences of heating, ventilation, air-conditioning, refrigeration, and related human factors to serve the evolving needs of the public and its ASHRAE members.
- International Code Council (ICC)—ICC's mission is to promulgate a comprehensive and compatible regulatory system for the built environment, through consistent performance-based regulations that are effective, efficient, and meet government, industry, and public needs.
- National Fire Protection Association (NFPA)—The mission of the international nonprofit NFPA is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating scientifically-based consensus codes and standards, research, training, and education.
- NSF International—NSF International is a not-for-profit, non-governmental organization and is the world leader in standards development, product certification, education, and risk-management for public health and safety. NSF develops national standards, provides learning opportunities through its Center for Public Health Education, and provides third-party conformity assessment services while representing the interests of all stakeholders.
- Sheet Metal and Air-Conditioning Contractor's National Association (SMACNA)—Located in headquarters outside Washington, DC, SMACNA, an international association of union contractors, has 1,965 members in 98 chapters throughout the United States, Canada, Australia, and Brazil. The voluntary technical standards and manuals developed by SMACNA Contractors have found worldwide acceptance by the construction community, as well as foreign government agencies. ANSI, the American National Standards Institute, has accredited SMACNA as a standards-setting organization. SMACNA does not seek to enforce its standards or provide accreditation for compliance. SMACNA standards and manuals address all facets of the sheet metal industry, from duct construction and installation to air pollution control, from energy recovery to roofing.
- SMACNA has a produced a manual, Kitchen Ventilation Systems and Food Service Equipment Fabrication and Installation Guidelines, that provides specific design and construction guidance for commercial kitchens.
- Sheet Metal Workers' International Association (SMWIA)—SMWIA represents 150,000 skilled crafts persons in the unionized sheet metal industry throughout the United States and Canada.