Restaurant and Commercial Kitchen Exhaust Hoods

"We Can Offer You a Complete and Affordable Solution to Kitchen Grease, Smoke and Odors Generated From Residential or Restaurant Cooking..."

Without an effective kitchen exhaust hood cleaning system, cooking grease and smoke causes grit and grime build-up on almost every structure these emissions come into contact with... that can cost you a lot of money in cleaning, maintenance and damage.

General Information...

Introduction

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 exhaust hoods. 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.

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.

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.

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 restaurant kitchen exhaust hood 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
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.

Replacement Air
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.

Owner/Facility Manager
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.

Architect
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
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.

Code Officials
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.

Engineer/System Designer
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.
 

Cleaning of Exhaust Systems

In accordance with Section 11.4 of the Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA Standard 96):

When to Clean? Who to Clean?
"Upon inspection, if found to be contaminated with deposits from grease-laden vapors, the entire exhaust system shall be cleaned by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction in accordance with Section 11.3.

What to Clean? How Clean is "Clean"?
"Hoods, grease removal devices, fans, ducts, and other appurtenances shall be cleaned to bare metal prior to surfaces becoming heavily contaminated with grease or oily sludge."
 

Inspection of Exhaust Systems

In accordance with Section 11.3 of the Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA Standard 96):

When to Inspect? Who to Inspect?
"The entire exhaust system shall be inspected by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction in accordance with Table 11.3."

Table 11.3
Exhaust System Inspection Schedule

Kitchen Hood Performance

KANSAS CITY, Mo. -- The position of appliances in a restaurant certainly doesn't figure into the dining plans of most customers.

But new research into the impact of diversity of equipment and its position on the performance of commercial kitchen hoods will result in cost savings and better operating kitchens, both of which may benefit customers.

Commercial kitchens typically use exhaust hoods to remove effluents, such as smoke, grease and moisture, generated by cooking operations.

To provide optimum energy efficiency, it is desirable to operate with the minimum exhaust flow needed to provide sufficient capture and containment of effluents. Higher exhaust usually leads to higher HVAC loads to condition replacement air.

Research comparing the impact of the position of a single appliance vs. multiple appliances under hoods on the minimum exhaust airflow required will be conducted by ASHRAE.

"The research will help manufacturers and installers of HVAC and kitchen ventilation equipment implement systems that are more cost competitive and provide cost savings for their customers," Richard Swierczyna, a principal investigator of the project, said. "Restaurant designers and consulting engineers will benefit by gaining a better knowledge of kitchen ventilation systems, which will help in providing better operating kitchens for their customers."

ASHRAE approved funding totaling $986,953 for eight research projects in the areas of indoor air quality, comfort and health, energy conservation, operating and maintenance tools, environmentally safe materials and design tools at its 2003 Annual Meeting held June 28-July 2.

Among them is 1202-TRP, Effect on Commercial Kitchen Hood Performance of Appliance Diversity and Position. The principal investigators are Swierczyna, Architectural Energy Corp., Boulder, Colo., and Donald Fisher, P.Eng., Fisher-Nickel Inc., San Ramon, Calif. The project is expected to take a year to complete at a cost of $105,033. It is sponsored by ASHRAE Technical Committee 5.10, Kitchen Ventilation.

The research will build on existing capture and containment studies from single appliance operations to multiple appliances underneath hoods. It also will examine how appliance positions underneath hoods may impact required capture and containment airflows.

"If ventilation manufacturers, kitchen designers and consulting engineers knew that they could specify operation of hoods with multiple appliances at lower flow rates, operations might benefit from lower energy costs while also realizing improved performance -- less heat gain and greater personnel comfort," Swierczyna said. "End-users would see these savings in the form of both lower first and operating costs over the lifetimes of equipment. The comfort issue also has economic consequences in terms of personnel performance and turnover costs."

Results of the study may be incorporated into codes, standards and design guides to assist code officials, commercial kitchen and building designers, consulting engineers and ventilation manufacturers with efficient restaurant design and operation.

Judi Dunlop, 09/03/2003, www.ashrae.org
 

About Cleaning

Kitchen exhaust cleaning is required by law for virtually every commercial cooking establishment in the United States. Restaurants, hospitals, hotels, employee cafeterias and other food-service locations have a "hood" and ductwork over the stove to exhaust smoke, steam, and fumes out of the building. These exhaust gases leave a residue on the inside of the ductwork. This is usually a grease residue of some sort, depending on the type of cooking. Char broilers commonly leave heavy black grease. Chinese cooking normally deposits a sticky or rubbery residue. When a charcoal or wood-burning stove is in use soot and ash residue builds up in the ductwork. Dishwashers leave heavy lint deposits.

When the buildup of grease becomes heavy, a fire hazard exists. Approximately one of three restaurant fires is caused by grease. A common scenario of how a kitchen exhaust fire starts is this:

A flame flares up on the stove.

The fire contacts the filters above the stove on the kitchen hood. The filters ignite.

Since the exhaust fan is on, drawing air into the hood, through the filters, and up the duct, the flame on the filters is pulled into the duct.

If significant grease residue exists on the duct interior, this can act as a fuel and the fire spreads up the duct, perhaps all the way into the fan. We have seen fire climb up a ten-story duct to the fan on the roof and burn up the fan.

Modern duct construction is designed to hopefully withstand such duct fires. The duct seams are welded to prevent grease or fire from leaking out and the shafts around the duct are made of fire- resistive materials. However, older buildings are still at risk, and even in modern ones the fire may leak out or could come out onto the roof via the fan.



When an exhaust system is cleaned regularly, however, the chances of a duct fire are extremely remote.

METHODS OF CLEANING

There are two primary methods of cleaning kitchen exhaust

ductwork:

Scraping.
Pressure washing or steam cleaning.
The primary method used is scraping. This is the more economical method and is extremely effective when done thoroughly. We know of no duct fires that have occurred because of using this method (unless it was done poorly). Scraping of duct systems complies with the Uniform Fire Code that is the governing fire code of the state of Washington. The cleaning method for kitchen exhausts most often used by Commercial Vent Vac is the scraping method.

The alternative to scraping is pressure washing or steam cleaning. This is a more costly and time-consuming technique, since it requires considerable prep work to control wastewater and more expensive equipment is involved. However, this method will clean ductwork down to "bare metal," which is the recommendation of the National Fire Protection Association (NFPA) as spelled out in NFPA Standard 96.

At Commercial Vent Vac, we frequently do pressure washing of kitchen exhausts as well as scraping. This is done for a variety of reasons. Sometimes the ductwork may be inaccessible for scraping or the client simply wants to take the extra precautionary step of having it cleaned to "bare metal."

HOW OFTEN SHOULD A KITCHEN EXHAUST BE CLEANED?

The most common cleaning frequency is every 3 months. This can vary, however. The kitchen exhaust systems that need cleaning most often are those over wood-burning or charcoal-burning stoves. These should be cleaned every month at least, and in some cases as often as every 2 weeks.

Below are various types of cooking establishments and their most commonly recommended cleaning frequencies.

Wood-burning or charcoal-burning stoves, charbroilers, 24-hour restaurants, and some hamburger places: 30 DAYS.
Many hamburger restaurants and fast-food locations: 60 DAYS.
Average restaurant, employee cafeteria, and hotel or hospital kitchen: 90 DAYS.
Pizza places, convalescent hospital, small snack bar, oven hood: 180 DAYS.
Hoods over non-grease-creating appliances, such as steam kettles, dishwashers, soup vats, etc. ONE YEAR.
Kitchen exhaust cleaning is a standard part of the routine maintenance of any cooking establishment. All kitchen managers and restaurant owners should be aware of its role in fire prevention and ensure it is done on a regular basis.
 

Related Links

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