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MECHANICAL EXHAUST VENTILATION SYSTEMS FOR RETAIL FOOD FACILITIES
Design, Calculations, and Operational Guidelines
California Conference of Directors of Environmental Health January 22, 2019
Page 2 of 30
TABLE OF CONTENTS
I. Background ........................................................................................................ 3
II. Purpose and Scope ............................................................................................. 3
III. Legal Authority and Applicable Codes and Standards… ......................................... 3
VI. Type I Hoods… .................................................................................................... 7
A. Unlisted Type I Hoods (Custom) .................................................................. 7
a. Extra Heavy Duty Cooking Appliances (Table 1) ....................................... 7
b. Heavy Duty Cooking Appliances (Table 2). .............................................. 7
c. Medium Duty Cooking Appliances (Table 3). ........................................... 8
d. Light Duty Cooking Appliances (Table 4)… .............................................. 8
B. Listed Hoods (UL 710)… .............................................................................. 8
C. Recirculating Systems (UL 710B). ............................................................... 8
D. Cooking Appliances with Reduced Grease Emissions (EPA 202 Test) ............. 8
E.
VII.
A. Unlisted Type II Hoods (Custom) ................................................................. 9
B. Listed Type II Hoods (UL 710)… ................................................................... 10
C.
VIII. Recommended Formulas for Specific Equipment .................................................. 10
XI. Exhaust Hood Installation Requirements… ............................................................ 17
XII. Eyebrow-Type Exhaust Hoods… ............................................................................ 17
XIII.
XIV. Water Wash-Type Exhaust Hoods… ....................................................................... 18
XV. Make-Up Air… ...................................................................................................... 19
APPENDIX I (Resources, Codes, Standards). .......................................................... 21
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MECHANICAL EXHAUST VENTILATION SYSTEMS FOR RETAIL FOOD FACILITIES
Design, Calculations, and Operational Guidelines
California Conference of Directors of Environmental Health
I. Background
Proper venting and capture of the gases, heat, grease, vapors, and smoke generated by cooking
equipment is important; not only for fire prevention and sanitation purposes, but also for
maintaining the health and well being of food service workers. In order to help prevent dangerous or
unhealthful conditions within a food facility, it is critical that exhaust ventilation systems be
designed, constructed, and operated in compliance with all applicable requirements.
II. Purpose and Scope
A. These guidelines are intended to assist in determining mechanical exhaust ventilation
requirements for equipment that generates grease, vapors, fumes, smoke, steam, heat,
and/or odors.
B. Exhaust ventilation systems shall a l s o conform to all local building and fire codes and have
all necessary approvals from the local building and fire authorities.
C. The requirements contained within this document represent minimum standards, which may
be superseded by local ordinances. Where there is a contradiction in the requirements, the
stricter should apply.
D. Due to the differing roles of the local enforcement agencies and local building departments,
not all health jurisdictions will be applying all portions of these guidelines.
III. Legal Authority and Applicable Codes and Standards
A. California Health and Safety Code, Division 104, Part 7, Chapter 6, Article 2, Section 114149 –
114149.3 (California Retail Food Code, Cal Code).
B. California Code of Regulations, Title 17, Article 10.4, Commencing with Section 13670.
C. California Code of Regulations, Title 24, Part 4, Chapter 5, Part II (California Mechanical Code,
CMC).
IV. Definitions
A. Backshelf (Noncanopy hood) - a hood that does not extend completely over the cooking
equipment. A noncanopy hood is designed to be as close as possible to the cooking surface.
This type of hood may also be referred to as a low proximity hood.
B. Canopy Hood – a hood designed so the inside edge overhangs or extends a
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horizontal distance not less than six inches beyond the outer edges of the cooking surface.
C. Compensating Hood – A hood that has an outside air-supply with air delivered below or within
the hood. Where makeup air is diffused directly into the exhaust within the hood cavity, it
becomes a short-circuit hood. This design shall provide no more than 10% of the exhaust
airflow, typically through four basic discharge methods: short-circuit, face-discharge, back-
discharge, and down-discharge. These methods may also be combined, such as a face and
down- discharge arrangement. Short-circuiting hoods shall be tested and listed by a qualified
testing agency and installed/operated according to the listing conditions.
D. Convection Oven – a gas or electric heated oven that uses a fan or blower to recirculate
the heat throughout the interior of the oven.
E. Double Island Canopy – two single island hoods installed back to back.
F. Downdraft Appliance – an appliance with an integral exhaust ventilation system that exhausts
cooking fumes across the cooking surface downward. This type of cooking appliance is
typically used for front of house cooking applications such as hibachi style tables.
G. Ducting – the conduit that is used to convey exhausted air from the exhaust hood to the
outside of the food facility.
H. Eyebrow Hood- An eyebrow hood is mounted directly to the face of an appliance, such as an
oven and dishwasher, above the opening(s) or door(s) from which effluent is emitted,
extending past the sides and overhanging the front of the opening to capture the effluent.
I. Grease Extractor – a series of baffles installed in the exhaust hood in such a way as to remove
grease from the exhausted air using centrifugal force.
J. Grease Filter – a device that is installed in the exhaust hood in such a way as to remove grease
from the exhausted air by entrapment, impingement, adhesion, or other similar means.
K. Hood – an air-intake device connected to a mechanical exhaust ventilation system for
collecting and removing cooking effluent which contains grease, vapors, fumes, smoke,
steam, heat, or odors which are generated by cooking equipment and warewashing
machines.
L. Listed Equipment – equipment and materials which, following evaluation and acceptance by
a qualified testing agency, are placed on a list of certification. The listing shows that the
equipment and materials comply with accepted national standards, which have been
approved or evaluated for conformity with approved, or national standards.
M. Pass-over Hood- A pass-over hood is a free-standing form of a backshelf hood constructed low
enough to pass food over the top.
N. Plenum – an air compartment or chamber to which one or more ducts are connected and
which forms part of the supply-air, return-air, or exhaust air system.
O. Portable – equipment having the properties of being portable, weighing less than 80 pounds,
not exceeding three feet in any plane, and having utility connections designed to be
disconnected or of sufficient length to permit equipment movement for cleaning.
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P. Recirculating Hood System (Ductless hoods or Ventless hoods) – a self-contained air exhaust
system that removes grease, vapors, fumes, smoke, steam, and odors from the exhausted
air; and then reintroduces the filtered air back into the food facility. The grease, vapors,
fumes, smoke, and steam are normally removed using a variety of systems such as water
sprays, electrostatic precipitators, or multiple filter banks. The odors are typically removed
using activated charcoal filters. Recirculating hood systems are not designed to eliminate
heat from the exhausted air. Recirculating hood systems are also known as ductless or
ventless hoods. These systems are certified under UL product categories KNKG (Commercial
cooking appliances with integral recirculating ventilation systems) or YZCT
(Hoods/recirculating systems for use with specified commercial cooking appliances).
Q. Single Island Canopy – a canopy hood that is mounted from the ceiling with all four sides
exposed. This installation can allow for display cooking.
R. Type I Exhaust Hood – a hood that is designed to collect and remove all types of cooking
effluent from the exhausted air.
S. Type II Exhaust Hood – a hood that is designed to collect and remove only steam, vapors, heat,
or odors.
T. Water-Wash-Type Exhaust Hood – a Type I hood which uses water to remove accumulated
grease from the grease extractors.
V. General Requirements
A. Cal Code requires the following:
1. Section 114149(a) “All areas of a food facility shall have sufficient ventilation to
facilitate proper food storage and to provide a reasonable condition of comfort for each
employee, consistent with the job performed by the employee.”
2. Section 114149.1(a) “Mechanical exhaust ventilation equipment shall be provided over
all cooking equipment as required to effectively remove cooking odors, smoke, steam,
grease, heat, and vapors. All mechanical exhaust ventilation equipment shall be
installed and maintained in accordance with the California Mechanical Code, except
that for units subject to Part 2 (commencing with Section 18000) of Division 13, an
alternative code adopted pursuant to Section 18028 shall govern the construction
standards.”
B. CMC Section 508.1 states:
1. “Type I hoods shall be installed at or above commercial-type deep- fat fryers, broilers,
grills, hot-top ranges, ovens, barbecues, rotisseries, and similar equipment that emits
comparable amounts of smoke or grease in a food-processing establishment. For the
purpose of this section, a food-processing establishment shall include a building or
portion thereof used for the processing of food but shall not include a dwelling unit.”
2. “Type II hoods shall be installed above equipment and dishwashers that generate
steam, heat, and products of combustion, and where grease or smoke is not present.”
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C. Type I Hood Requirement: There are five methods to comply with requirements for
equipment that emits smoke or grease.
1. Unlisted Type I hoods built in accordance with CMC Section 508
2. Listed Type I hoods (UL 710)
3. Recirculating systems (UL 710B)
4. Cooking appliances with reduced grease emissions (EPA 202 test)
5. Downdraft appliances
D. Type II Hood Requirement: There are three methods to comply with requirements for
equipment that generate steam, heat, and products of combustion, where grease or smoke
is not present.
1. Unlisted Type II hoods built in accordance with CMC Section 508
2. Listed Type II hoods
E. CMC Section 303.1 requires listed ventilation equipment to be installed and used in
accordance with the manufacturer’s installation and operating instructions. A copy of the
instruction shall be readily available for review by the enforcement officer.
F. Special Cooking Equipment and Operations
1. Table-top cooking operations:
Cooking equipment, which is located at customer dining tables, shall be provided with
approved mechanical exhaust ventilation. Korean barbecues and Japanese Teppan-
style cooking are examples of these table-top cooking operations.
2. Table-side serving display operations:
Traditional serving display operations, such as flambéing, may not be required to
provide mechanical exhaust ventilation, unless excessive amounts of smoke, grease,
steam, vapors, and/or heat are emitted. These serving display operations are not
intended to cook the food, but merely "finish off" the product prior to serving. Local
building and fire officials should be contacted for their requirements.
G. Exemptions From Providing Mechanical Exhaust Ventilation
1. Cal Code section 114149.1 (c) states: “This section shall not apply to cooking equipment
when the equipment has been submitted to the local enforcement agency for evaluation,
and the local enforcement agency has found that the equipment does not produce toxic
gases, smoke, grease vapors, or heat when operated under conditions recommended by
the manufacturer. The local enforcement agency may recognize a testing organization to
perform any necessary evaluations.”
2. CMC Section 508.1 lists when hoods are required to be installed. Exceptions to this
requirement are listed as follows:
a. Cooking appliance that is in accordance with UL 710 B for reduced emissions where
the grease discharge does not exceed 2.9 E-09 ounces per cubic inch (oz/inᵌ) where
operated with a total airflow of 500 cubic feet per minute (cfm).
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b. Recirculating systems listed in accordance with UL 710B and installed in accordance
with CMC Section 516.0.
c. Dishwashing machines connected to a Type II duct system and exhausted directly to
the outdoors.
d. Dishwashing machines with a self-contained condensing system listed in
accordance with UL 921 and installed in a space where the HVAC system has been
engineered to accommodate the latent and sensible heat load emitted from such
appliances.
VI. Type I Hoods
A. Unlisted Type I Hoods (Custom)
1. Type I hoods for use over charcoal and other solid-fuel charbroilers shall be provided with
separate exhaust systems (e.g., separate exhaust duct and exhaust fan).
2. When different types of cooking equipment are installed under a common hood, the
entire hood shall be designed using the formula that produces the highest flow rate. For
example, a single hood installed over a gas charbroiler, fryer, and range, shall be
designed using the formula for the charbroiler (Table 2).
The duty level for the hood shall be the duty level of the appliance that has the highest
(heaviest) duty level of appliances installed underneath the hood. The tables below are
used to calculate the minimum exhaust CFM for custom hoods only. CMC Section
508.10.1
Exhaust CFM = AIRFLOW x Length of hood
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a.Extra-Heavy-Duty-Cooking Appliances
The minimum net airflow for hoods used for:
•solid fuel cooking appliances (charcoal, briquette, and mesquite)shall be in accordance with Table 1.
Table 1
b.Heavy-Duty Cooking Appliances
The minimum net airflow for hoods used for:
•gas under-fired broilers
•gas chain (conveyor) broilers
•electric and gas wok ranges
•electric and gas over-fired (upright)broilersshall be in accordance with Table 2.
Table 2
c.Medium-Duty Cooking Appliances
The minimum net airflow for hoods used for:
•electric and gas hot-top ranges
•gas open-burner ranges (with or without oven)
•electric and gas flat griddles
•electric and gas double sidedgriddles
•electric and gas fryers (including open deep fat fryers, donut fryers, kettle
fryers and pressure fryers)
•electric and gas conveyor pizza ovensshall be in accordance with Table 3.
TYPE OF HOOD
TYPE OF HOOD foot per minute per linear foot of
400
400
Not permittedSingle islandcanopy 600
Wall-mountedcanopy 400
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Table 3
d.Light-Duty Cooking Appliances
The minimum net airflow for hoods used for:
•gas and electric ovens (including standard, bake, roasting, revolving, retherm,
convection, combination convection/steamer, rotisserie, countertop
conveyorized baking/finishing, deck, and pastry)
•discrete element ranges (with or without oven)
•electric and gas steam-jacketedkettles less than 20 gallons (76 L)
•electric and gas pasta cookers
•electric and gas compartment steamers (both pressure and atmospheric)
•electric and gas cheesemelters
•electric and gas tilting skillets(braising pans)
•electric and gas rotisseries
•electric and gas salamanders
shall be in accordance with Table 4.
Table 4
B.Listed Type I Hoods (UL 710)
a.Hoods that have been evaluated and listed shall be sized and installed in
accordance with the terms of their listing and according to the
manufacturer’s instructions.
b.Refer to manufacturer specifications regarding maximum cooking temperature for
specific equipment.
TYPE OF HOOD foot per minute per
TYPE OF HOOD per minute per linear
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C.Recirculating Systems UL 710B – CMC Section 516
1.Recirculating systems that have been evaluated and listed u n d e r U L 7 1 0 B shall be
sized and installed in accordance with the terms of their listing, according to the
manufacturer’s instructions, and CMC Section 516.
2.Since a nonducted exhaust system does not normally remove the heat from the exhausted
air, additional air conditioning may be required.
D.Cooking appliances with reduced grease emissions (also known as EPA 202 test)
1.Cooking appliances that are in accordance with UL 710B for reduced emissions where the
grease discharge does not exceed 2.9 E-09 ounces per cubic inch (oz/in3) (5.0 E-06 kg/m3)
where operated with a total airflow of 500 cubic feet per minute (cfm) (0.236 m3/s) are not
required to be under a hood (CMC Section 508.1).
2.These appliances shall be installed in accordance with the terms of their listing and according
to the manufacturer’s instructions.
E.Downdraft appliances – CMC Section 518
1.A downdraft appliance ventilation system has been listed as being capable of capturing and
containing the effluent discharge from the appliance it is serving. These appliances shall be
installed in accordance with the terms of their listing and according to the manufacturer’s
instructions.
2.Typical downdraft appliance ventilation systems includes both a cooking appliance and
ventilation system, such as tables that have built-in downdraft exhaust systems with two fans.
One fan pushes the smoke and the second fan draws air across the table. The cooking vapors are
captured and carried to a grease duct that is attached to the bottom of the table and are
exhausted outdoors.
VII.Type II Hoods
A.Unlisted Type II Hoods (Custom)
1.Type II hoods shall be installed above equipment and dishwashers that only generate
steam, heat, and products of combustion, where grease or smoke is not present.
2.The table below is used to calculate the minimum exhaust CFM for custom hoods only that
are serving cooking appliances. CMC Section 508.10.1
Exhaust CFM = AIRFLOW x Length of hood
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Light-Duty Cooking Appliances The minimum net airflow for hoods used for:
• gas and electric ovens (including standard, bake, revolving, retherm, convection,
combination convection/steamer, countertop conveyorized baking/finishing,
deck, and pastry)
• discrete element ranges (with or without oven)
• electric and gas steam-jacketed kettlesless than 20 gallons (76 L)
• electric and gas pasta cookers
• electric and gas compartment steamers(both pressure and atmospheric)
• electric and gas tilting skillets (braising pans)
shall be in accordance with Table 4.
Table 4
TYPE OF HOOD foot per minute
per linear foot of
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3.“The net airflow for Type II hoods used for dishwashing equipment shall be not less than
200 cubic feet per minute (0.094 m3/s) per linear foot (m) of hood length.” (CMC Section
508.10.1.6)
B.Listed Type II Hoods (UL 710)
1.Hoods that have been evaluated and listed shall be sized and installed in accordance
with the terms of their listing and according to the manufacturer’s instructions.
C.Dishwashing machines with a self-contained condensing system (UL 921)
1.“Dishwashing machines with a self-contained condensing system listed in accordance
with UL 921 and installed in a space where the HVAC system has been engineered to
accommodate the latent and sensible heat load emitted from such appliances as
approved by the Authority Having Jurisdiction.” This is an exception to the hood
requirement in CMC Section 508.1.
2.Dishwashing machines under this standard shall be provided with an interlocking device
to prevent opening of the appliance prior to completion of its cycle.
VIII.Recommended Formulas for Specific Equipment
The following list is to be used as a guide to determine which hood type and table to use.
Equipment Hood Type Table to Use
•
•
•
•
•
•
•
(tortillas, pastries, rolls, sandwiches from precooked meats and
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Clam Shell Grill (large), for cooking grease producing foods
(multiple hamburgers)
I 3
Crepe Maker (no meats)
•
•
•
•
•
•
•
•#
Without grease vapor generation
•Electric convection oven (max 250°F) ie. For baking
bread products
•Gas or electric greater than 250°F
ie. standard, bake, revolving, retherm, convection, combination
convection/steamer, countertop conveyorized baking/finishing,
deck, and pastry
*
II
–
4
Ovens: With grease vapor generation
•Gas or electric (greater than 250°F)
ie. standard, bake, roasting, revolving, retherm, convection,
combination convection/steamer, rotisserie, countertop
conveyorized baking/finishing, deck, and pastry
I 4
•Gas or electric conveyor pizza ovens I 3
•
•
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•For heating non-grease producing foods (tortillas,
pastries, rolls, sandwiches from precooked meats and
cheeses)
•For heating grease producing foods
*# –
4
•
•
•
•
•
•Without external grease vapor release II 4
•Electric * –
•
Rotisserie
•Open or high temp I 4
•Enclosed with max. ambient cavity temperature of 250°F * –
Skillet (electric and gas tilting or braising) I 4
Smokers
•Gas-operated utilizing solid fuel for flavoring I 2
•Solid Fuel I+ 1
Steam Cooker II 4
Steam Table (hot holding only) * –
Toaster (bread only)
•Portable * –
•
Waffle Cone Maker / Waffle Iron
•Portable * –
•Nonportable II 4
+Cooking equipment that uses solid fuel shall be provided with a separate exhaust system.
# Multiple units of the heating/cooking equipment proposed may be approved by the
enforcement agency where it has been demonstrated that latent heat and excessive
moisture has been sufficiently addressed.
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*Equipment marked with an asterisk typically does not need mechanical exhaust
ventilation. However, the following criteria should be taken into consideration when
determining the need for mechanical exhaust ventilation:
•Installation of other unventilated heat generating equipment in the same area,
e.g., refrigeration condensers, steam tables, or counter-top equipment;
•Presence of heating/cooling (HVAC) system;•Size of the room or area where the proposed equipment will be installed, includingceiling height;
•How the proposed equipment will be operated, e.g., the types of food prepared, how
often, etc.;
•Relative size of the proposed equipment, e.g.,physical size and weight, BTU’s/KW’s;
•Nature of the emissions, e.g., grease, heat, steam, etc.;
•Temperature at which the proposed equipment operates. Cooking equipment that
has a factory-set thermostat that cannot exceed 250°F normally does not need
mechanical exhaust ventilation;
•Method of producing heat, e.g., gas, electricity, solid fuel, etc.
•Adequate amount of general ventilation: In poorly ventilated confined areas where
the proposed equipment (like ovens and low-temp. dishwashers) is located,
adequate general ventilation could be provided by a ceiling or wall exhaust fan that
provides an air change rate of 3-5 minutes per change.
IX.Grease Filters
A.This section applies to grease filters installed in a listed or unlisted Type I hood. Refer to
the listing and manufacturer’s installation instructions for the grease filters within
downdraft appliances and recirculating systems.
B.Type I hoods shall be equipped with approved grease filters listed in accordance with UL
1046 to remove grease from the exhausted air.
C.Grease filters are designed to remove grease particles from the exhaust air stream.
Exhaust systems that have broken, missing, or undersized filters are prone to
collect accumulations of highly combustible grease deposits throughout the entire duct
system. Because of the chimney effect created in vertical ductwork, a very intense
rapidly spreading flash fire can engulf the entire system.
D.The most common grease filters currently in use are the baffle-type. Baffle-type filters
simplify the cleaning process since most of the grease deposits run off the baffles to a
collection device. The old style mesh-type filters are not acceptable in new installations.
NFPA 96, ANSI NSF Standard 2, and UL 1046 no longer recognize the old style mesh type
filters. They may present a fire hazard and decrease airflow as they become clogged
with grease.
E.Mesh filters shall not be used unless evaluated as an integral part of a listed exhaust hood
or listed in conjunction with a primary filter in accordance with UL 1046.
F.Grease filters and extractors shall be of such size, type, and arrangement as will permit
the required quantity of air to pass through such units at rates not exceeding those for
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which the filter or extractor was designed and approved. The optimum operating
velocities, measured in feet per minute (FPM), vary from filter to filter. Therefore, the
manufacturer's specifications should be consulted to obtain the appropriate rates for
each specific filter.
G.Number of Filters Required
1.It is important to select the proper number of grease filters for the hood. Too few
filters increase the resistance to airflow and raise the filter cleaning frequency.
2.The minimum required number of filters for a particular hood can be calculated
by dividing the total volume of air to be exhausted, in CFM, by the optimum
operating velocity of the filter, in FPM. This number is then divided
by the actual square footage of the filter (excluding the frame). The resulting
figure represents the minimum number of filters required to efficiently remove
the grease from the exhausted air.
Example:
Assume the following:
•An exhaust hood with a minimum required airflow of 3,250 CFM.
•Baffle type filters with a nominal size of 16" x 20", have an actual filtering
surface of 14" x 18". (Nominal size minus the frame equals the actual filtering
area.)
•An optimum operating velocity of 360 FPM for the filter.
Volume of Air Exhausted = Filter Area Needed (sq. ft.)
Operating Velocity of Filter(FPM)
3,250 CFM = 9 sq. ft.
360 FPM
Next, convert the actual filter area to square feet:
14 in. x 18 in. = 252 sq. in.
252 sq. in. = 1.75 sq. ft.
144 sq. in./sq. ft.
Then divide the 9-sq. ft. of needed filter area by sq. ft. per filter:
9 sq. ft. = 5 filters
1.75 sq. ft.
Therefore, in this example, 5 filters would be required to provide adequate
removal of the grease.
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H.Any space in the hood not occupied by a filter should be blanked off with sheet metal.
Blanks may be placed above nongrease producing equipment such as a steam table, in
order to achieve a better draw where it is needed the most. As much as possible, the
blanks should be divided equally between the filters. This will ensure optimum
performance and will equalize the air velocity over the entire length of the hood opening.
I.It is important to install filters at the ends of the hood. However, grease filters should not
be installed directly over a broiler flue, or any other flue from cooking equipment. Hot
gases can make the filters very difficult to clean and may damage them.
J.The distance between the grease filters and the cooking surface shall be a minimum of
18 inches. Grease filters used with charcoal or charcoal-type broilers, including gas or
electrically heated charbroilers, the distance shall be a minimum of 4 feet. Where
grease filters are listed for separation distances less than the requirement, the listing
requirements shall be permitted. Grease filters supplied as part of listed hood
assemblies shall be installed in accordance with the terms of the listing and
manufacturer’s installation instructions.
K.Filters shall be installed at an angle not less than 45 degrees from the horizontal and
shall be equipped with a drip tray beneath the lower edge of the filter. This enables the
grease to be collected in the drip tray and avoids grease dripping into food, or on food
preparation surfaces.
L.All grease collecting equipment shall be accessible for cleaning. Filter units shall be
installed in frames or holders with handles so as to be readily removable without the use
of tools, except where the system is designed for in -place cleaning.
M.Proper hood design will keep the temperature at the filters less than 200° Fahrenheit.
When the temperature at the filters is less than 200°F, the grease deposits will be
brownish in color and can be easily removed. When the temperature exceeds 200°F,
the grease deposits tend to bake on the filters. The color of the deposits will darken and
become extremely difficult to remove.
N.Filter equipped exhaust systems shall not be operated with damaged or missing filters.
X.Exhaust Hood Ducting
A.Ducting shall be installed in compliance with applicable sections of CMC, and local
building and fire codes.
B.This section applies to ducting serving a listed or unlisted Type I or Type II hood. Refer to the
listing and manufacturer’s installation instructions for the duct serving downdraft
appliances.
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C.A separate duct system shall be provided for each Type I hood, except that a single duct
system may serve more than one hood located in the same story of the building,
provided that all hoods served by the system shall be located in the same room or
adjoining rooms.
D.Exhaust ducts from hoods shall be totally separated from all other ventilation systems.
E.If the hood length exceeds 12 feet, it is necessary to provide two discharge ducts from
the top of the hood to the main exhaust duct. For listed hoods, refer to the
manufacturer’s installation and operating conditions to determine if a distance of
greater than 12 feet between ducts is permitted.
F.Exhaust outlets for the exhaust hood ducting shall extend through the roof unless
otherwise approved by the local building official. Such extension shall be at least 24
inches above the roof surface; at least ten feet from an adjacent building, adjacent
property line, or air intake into any building; and shall be located at least ten feet above
the adjoining grade level. However, exhaust outlets for ducting may terminate at least
five feet from an adjacent building, adjacent property line, or air intake into a building if
the air from the exhaust outlet is discharged away from such locations.
G.Exposed duct systems serving a Type I hood shall have a clearance of at least 18 inches
from unprotected combustible construction. This clearance may be reduced to not less
than three inches, provided the combustible construction is protected with material
required for one-hour fire-resistive construction. Hoods less than 12 inches from the
ceiling or wall, including the space between the duct and the duct shaft, shall be flashed
solidly. Flashing shall be of either the same materials used in the construction of the
hood, or of other materials conforming to one-hour fire-resistive construction. Check
with your local building and fire authorities to determine other acceptable means of
meeting this requirement.
H.Duct Sizing: Duct systems serving a Type I hood shall be designed and installed in a
manner to provide an air velocity within the duct system of not less than 500 FPM and not
to exceed 2,500 FPM.
1.The duct leading from the exhaust hood to the exhaust outlet shall be sized
correctly. The velocity of the exhaust air shall be high enough to minimize
condensation on the various parts of the duct system.
2.The following formula shall be used to determine the correct duct size:
Volume of air exhausted (CFM) = Duct area needed (sq. ft.)
Duct Velocity (FPM)
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I.A circular duct requires a smaller space. If rectangular ducts are used, they should be
as square as possible.
J.The bends and elbows of the ductwork should be kept at a minimum. When elbows are
used, a radius of 2 to 2 1/2 times the duct diameter is recommended. This will minimize
the resistance against which the blower must move the air.
K.Duct systems serving a Type I hood shall be constructed and installed so that grease will
not collect in any portion of the ducting. The ducting shall slope not less than 1/4 inch
per linear foot toward the hood or toward an approved grease reservoir. Where horizontal
ducts exceed 75 feet in length, the slope shall be not less than one inch per linear foot.
L.Any portion of the ducting that is inaccessible from the duct entry or discharge shall be
provided with cleanout openings. Cleanout openings shall be equipped with tight fitting
doors that are constructed of the same material and thickness as the ducting. The doors
shall be equipped with latches that will hold the door tightly closed. Doors
shall be designed so that they can be opened without the use of tools.
M.Ducts and plenums shall be constructed of carbon steel not less than .055 inch (No. 16
gage), or stainless steel not less than .044 inch (No. 18 gage) in thickness.
N.All seams and joints shall have a liquid-tight, continuous external weld.
O.All ducting that is exposed to the outside atmosphere and subject to corrosion shall be
protected against such corrosion. Galvanization of metal parts, protection with
noncorrosive paints, or installation of waterproof insulation are acceptable methods of
protection.
XI.Exhaust Hood Installation Requirements
A.This section applies to ducting serving a listed or unlisted Type I or Type II hood. Refer to
the listing and manufacturer’s installation instructions for the installation requirements
for listed hoods.
B.Canopy hoods shall overhang, or extend a horizontal distance of at least 6 inches
beyond the outer edge of the cooking surfaces on all open sides. This distance is to be
measured from the inside lip of the hood.
C.The vertical distance between the lower lip of the hood and the cooking surface shall
not exceed 4 feet.
D.Every portion of a Type I hood shall have a clearance from combustible construction of
not less than 18 inches. This clearance may be reduced to not less than three inches
provided the combustible material is protected with materials as specified for one-hour
fire-resistive construction on the hood side.
E.Canopy hoods shall be flashed to the ceiling and adjacent walls. The flashing shall be
Mechanical Exhaust Ventilation SystemsDesign, Calculations, and Operational Guidelines 2019
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constructed of the same material and thickness as the hood. See Figures 4 and 5 for
illustrations of the flashing methods.
F.Exhaust hoods shall be constructed of galvanized steel, stainless steel, or copper in
compliance with the CMC.
G.All joints and seams shall be liquid-tight and smooth for ease of cleaning. Approved
construction methods and materials shall be used for sealing joints and seams.
H.Pop rivets, metal screws, or other similar exposed fasteners shall not be used on the
internal surfaces of a hood.
I.Every hood shall be securely fastened in place by noncombustible supports.
Exposed support hangers shall be of an easily cleanable design and construction.
Threaded rods and chains are not acceptable.
J.All conduit and fire protection piping shall be installed outside the hood, except for
conduit or fire protection piping that leads from outside the hood directly to approved
luminaires or fire protection nozzles located inside the hood. All conduit or piping
installed inside the hood shall be installed at least 3/4 inch away from the hood
surface to facilitate cleaning.
XII.Eyebrow-Type Exhaust Hoods
A.Eyebrow hoods are acceptable for use with either Type I or Type II hoods, for medium or
light duty cooking appliances only.
B.Eyebrow hoods shall be installed in accordance with CMC Section 508.8.
XIII.Noncanopy-Type Exhaust Hoods
A.Noncanopy hoods shall be installed and sized in accordance with the manufacturer’s
installation instructions.
B.Noncanopy hoods shall be installed with the edge of the hood set back not more than 1
foot from the edge of the cooking surface and the vertical distance between the lip of the
hood and the cooking surface shall not exceed 3 feet.
C.Noncanopy hoods are not permitted to be installed for “Extra Heavy Duty” cooking
equipment. The volume of air exhausting through the noncanopy-type hood to the duct
system shall be as follows:
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21 32
D.Listed
noncanopy exhaust hoods and filters shall be sized and installed in accordance with the
terms of their listing and the manufacturer’s installation instructions.
XIV.Water-Wash-Type Exhaust Hoods
A.This section applies to listed Type I hoods. Refer to the listing and manufacturer’s
installation instructions for the installation requirements.
B.Water-wash-type hoods operate under the following principles: As the exhausted air
moves at a high velocity past a baffle system, the heavier-than-air particles of grease
are thrown out of the airstream by centrifugal force. The extracted grease is collected in
grease gutters within the hood until removed by the daily cleaning cycle. The cleaning
cycle is initiated when the exhaust hood is turned off. Hot detergent water is
automatically sprayed onto the baffle system, thereby removing the grease deposits
from the baffles. This wastewater is then drained off to the sewer or other approved
waste removal system.
C.In order to protect the potable water supply, an approved backflow prevention
device, such as a reduced pressure principle device (RP device), is required to be
installed on the water inlet pipe, prior to the detergent pump solenoid.
D.The wastewater from a water-wash-type hood shall be drained through an air gap
separation into an approved receptacle, such as a floor sink.
XV.Make-up Air
A.Each room provided with an exhaust system shall have supplied to the room an amount
of make-up air equal to the amount of air to be exhausted. If make-up air were not
provided, the building would be under a negative pressure which could cause the
following problems:
1.The exhaust fan would not be capable of exhausting the design volume of air
because the air would not be available.
Duty level for cooking equipment Minimum air flow exhausted per linear foot of cooking equipment
Heavy Duty 400 CFM/Foot
Medium Duty 300 CFM/Foot
Light Duty 250 CFM/Foot
Mechanical Exhaust Ventilation SystemsDesign, Calculations, and Operational Guidelines 2019
22 32
2.Negative pressure would cause improper venting of water heaters, space
heaters, or other individually vented gas appliances in the building.
3.A negative pressure will cause a surge of unconditioned outside air into the
building whenever the doors are opened, which may also allow the entrance of
flies into the facility.
B.In order to provide an efficient air exchange system, the following factors should be
taken into consideration when evaluating a make-up air system:
1.The number and location of return air registers should be such as to provide
uniform distribution of make-up air throughout the facility, taking into
consideration cross drafts, room configurations, and required air flows.
2.The use of properly designed registers and diffusers will help to slow down the air
velocity and evenly distribute the make-up air.
3.The make-up air registers should be located so as to prevent a short-circuiting
of the air being supplied for the exhaust system.
C.Windows and doors shall not be used for the purpose of providing make-up air.
D.The exhaust and make-up air systems shall be connected by an electrical interlocking
hardwired connector so that one system cannot be operated when the other system is
off.
E.Compensating hoods shall extract no more than 10% of their required exhaust airflow
from the kitchen area around the hood. Compensating hoods, that have been evaluated
and listed, shall be sized and installed in accordance with the terms of their listing, and
according to the manufacturer’s instructions.
XVI.Fire Extinguishing Systems
A.Approved automatic fire extinguishing systems shall be provided for the protection of
commercial-type cooking equipment. The requirement for protection does not
include equipment that does not create or generate grease-laden vapors, such as steam
kettles and steam tables.
B.Deep fat fryers, ranges, griddles, broilers, and other cooking equipment which may act
as a source of ignition for grease in the hood, grease removal device, or duct, shall be
protected by approved fire extinguishing equipment installed in accordance with the fire
code adopted by the jurisdiction. Necessary approvals shall be obtained from the local
fire authorities prior to putting equipment into operation.
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Resources
APPENDIX I
PG&E Food Service Technology Center www.fishnick.com
UL Commercial Cooking Marking & Application Guide
https://www.ul.com/wp-content/uploads/2014/04/CommercialCooking_AG1.pdf
IAPMO Code Process http://codes.iapmo.org/
Installation Codes and Standards
California Mechanical Code http://epubs.iapmo.org/2016/CMC/#p=10
Uniform Building Code
Uniform Fire Code
Uniform Plumbing Code
International Building
Code
International Fire Code
International Mechanical Code
Uniform Plumbing Code
International Plumbing Code
International Fuel Gas Code
National Electrical Code (NFPA 70)
Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA
96)www.NFPA.org/96
Product Standards Used by Listing Agencies for Cooking System Components
ANSI Z83.11, CGA 1.8 - Gas Food Service Equipment
ANSI/NSF 2 – Food Service Equipment
ANSI/NSF 4 – Commercial Cooking, Rethermalization and Hot Food Holding and Transport Equipment
ASTM E814 – Fire Tests of Through Penetration Fire Stops
ASHRAE 154- www.ashrae.org
EPA Test Method 202
•UL Product Category Code KNLZ = Commercial Cooking Appliances with Integral
Systems for Limiting Emission of Grease Laden Air
IAPMO PS 98 – Backflow Protection for Grease Fire Suppression Systems ICBO
AC101 – Grease Ducts, Flexible Enclosure Systems
ICBO AC105 – Recirculating Commercial Kitchen Hoods
ICBO AC121 – Grease Duct Systems, Self-Enclosed
UL 197 – Commercial Electric Cooking
Appliances UL 296 – Oil Burners
UL 300 – Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking
Page 24 of 32
Areas UL 705 – Power Ventilators
UL 710 – Exhaust Hoods for Commercial Cooking
Equipment UL 710B – Recirculating Systems
•UL Product Category Codes:
KNKG = Commercial Cooking Appliances with Integral Recirculating Ventilation Systems
YZCT = Hoods/Recirculating Systems for Use with Specified Commercial Cooking
Appliances
UL 762 – Power Ventilators for Restaurant Exhaust Appliances
Page 25 of 32
UL 795 – Commercial-Industrial Gas Heating
Equipment UL 921- Commercial Dishwashers
UL 1046 – Grease Filters for Exhaust Ducts
UL 1254 – Pre-Engineered Dry Chemical Extinguishing System Units
UL 1479 – Fire Tests of Through Penetration Fire Stops
UL 1570 – Fluorescent Light Fixtures
UL 1571 – Incandescent Light Fixtures
UL 1572 – High Intensity Discharge Fixtures
UL 1978 – Grease Ducts
UL 2162 – Wood-Fired Baking Ovens – Refractory Type
UL 2221 – Fire Endurance Performance of Grease Duct Enclosure Assemblies Grease Ducts
Page 26 of 32
.... .....
Figure 1.
Canopy Hood
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Figure 2
The distance between the lower lip of the hood and the cooking surface shall not exceed 4 feet.
.
r • .. .•
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Page 30 of
Figure 5
Hood flashing
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Figure 7
Type II Eyebrow at Dishwasher openings