CMC · California Mechanical Code
Termination rules and rooftop/upblast fan clearance for hood exhausts
Commercial kitchen exhausts must terminate outdoors and meet specific horizontal and vertical clearances: Type I rooftops need 10 ft to intakes/adjacent buildings, 5 ft to combustible structures, 3 ft vertical separation to nearby intakes, and hinged upblast fans must locate ductwork ≥18 in above the roof and discharge ≥40 in above the roof; Type II rooftop outlets must be directed away from roof surfaces within 40 in and moisture outlets must not discharge over public ways.
Last reviewed: July 6, 2026
What the code requires — plain English
Type I hood exhausts must terminate to the outdoors, either with a fan or a duct, through the roof or through a wall, and rooftop terminations must meet specific horizontal and vertical clearances, grease‑drain and grease‑collection requirements, and upblast‑fan clearances. See § 510.9 and § 510.9.1 for Type I details.
Type II hood exhausts must terminate per the general exhaust termination distances in Chapter 5 and, for rooftop terminations, be discharged away from roof surfaces within 40 inches; moisture‑conveying Type II outlets (e.g., dishwasher steam) must not terminate over a public way or a location where condensate/vapor creates a nuisance or hazard. See § 519.5.
The single most important rule: place hood exhaust outlets so their discharge is directed away from people and air intakes and meet the minimum horizontal and vertical separation distances specified in § 510.9.1 (Type I) and § 519.5 (Type II).
Requirements in detail
Scope and controlling sections
- Type I hood exhaust termination — requirements and rooftop clearances are set in § 510.9 and § 510.9.1.
- Type II hood exhaust termination — termination rules, including rooftop discharge geometry, are in § 519.5.
Bolded key terms: Type I hood, Type II hood, upblast fan, grease collection device, air intake (FAI).
Decision‑relevant clearances and dimensions
| What you must measure | Required minimum / condition | Code Reference |
|---|---|---|
| Horizontal from outlet to adjacent buildings, property lines, and air intakes (Type I rooftop) | 10 feet (3048 mm) | § 510.9.1(1) |
| Horizontal from outlet (fan housing) to combustible structure (Type I rooftop) | 5 feet (1524 mm) | § 510.9.1(2) |
| Vertical separation above any air intakes within 10 ft of outlet (Type I rooftop) | 3 feet (914 mm) | § 510.9.1(3) |
| Ductwork distance from roof surface where fan attaches (upblast fan) | 18 inches (457 mm) minimum | § 510.9.1(8)(a) |
| Fan discharge clearance from roof surface (upblast fan) | 40 inches (1016 mm) minimum | § 510.9.1(8)(b) |
| Type II rooftop discharge distance from roof surfaces | Directed away within 40 inches (1016 mm) | § 519.5 |
| Grease drainage/collection device properties (near termination) | Must drain to a noncombustible, closed, rainproof collection container and not inhibit fan performance | § 510.9.1(4)–(6) |
Notes on measurement:
- Horizontal clearances (feet) are measured from the outlet’s closest edge to the referenced object (adjacent building, property line, or intake). See figure guidance in the code for intake angle adjustments for wall terminations.
- The 40‑inch upblast discharge requirement is measured from the roof surface to the discharge point as shown in the upblast‑fan figure referenced by § 510.9.1.
Upblast fan specifics
- Upblast fans used for Type I hoods must be listed for commercial cooking equipment, be hinged, have a flexible weatherproof electrical cable, and include a service hold‑open retainer to permit inspection/cleaning. Installation must meet § 510.9.1(8) and § 511.1.1.
- Where the fan mounts to the duct, the duct must be ≥ 18 inches above any roof surface; the fan discharge must be ≥ 40 inches above roof surface. Do not install upblast fans so their discharge impinges on the roof. § 510.9.1(8)(a–b).
- Upblast fans must provide grease drainage to a visible, readily accessible receptacle (drain not exceeding 1 gallon (4 L) for the fan) per fan requirements in § 511.1.1 and § 511.1.3.1.
Grease drainage and collection at terminations
- Any traps or low points near terminations must be arranged to drain grease into an approved collection container that is noncombustible, closed, rainproof, and structurally sound, and not combustible. § 510.9.1(4).
- Grease collection devices shall not inhibit fan performance. § 510.9.1(5–6).
Exceptions & special cases
- Wall terminations (Type I) follow a different geometry and clearance method (10 ft minimum to adjacent buildings/property lines/openings; additional height offsets for intakes above the plane of the exhaust). See § 510.9.2 for the angled‑height calculation and figure.
- Type II roof terminations: rooftop discharge must be directed away from roof surfaces within 40 inches; moisture‑conveying Type II (e.g., dishwasher exhaust) must not terminate over a public way or over an area where condensate/vapor could create a nuisance or hazard. § 519.5.
- A listed alternative fan or extended duct is permitted if it meets the vertical/horizontal separation, intake separation, and § 511.1.3 criteria. See § 510.9.1(9).
- Vibration isolation connectors listed for exterior roof locations are permitted when required for vibration control (§ 510.9.1.1). Access and safe work surfaces for fan inspection/cleaning are required (§ 510.9.1.2).
Common mistakes
- Measuring from the wrong point: distances must be measured from the exhaust outlet or fan housing edge — not the hood, not the stack base. Confirm the exact outlet plane per the figure in § 510.9.1.
- Confusing roof plane vs. roof surface: the code’s 18 in and 40 in clearances are relative to the roof surface at the point of the fan/attachment, per § 510.9.1(8).
- Forgetting grease‑drain requirements: terminating fans and ducts that collect grease must drain to approved containers — an often‑missed inspection item under § 510.9.1(4).
- Treating Type II steam/moisture outlets like Type I grease outlets: Type II moisture outlets must not discharge over public ways or create nuisance hazards — see § 519.5.
- Not providing safe access for fan inspection/cleaning — required in § 510.9.1.2.
Worked example — rooftop upblast fan for a restaurant hood
Scenario: A restaurant installs a Type I hood with an upblast fan on a flat roof. The rooftop has an adjacent HVAC fresh‑air intake located 8 feet horizontally from the fan centerline. The fan discharge outlet will be 36 inches above the roof surface.
Minimum horizontal clearance to the air intake: 10 ft required by § 510.9.1(1). At 8 ft, the planned location is noncompliant.
- Fix options: move the fan so the horizontal separation to the intake ≥ 10 ft, or reroute the discharge/extend duct so the outlet point is farther from the intake (ensuring the extended duct still meets other fan rules in § 510.9.1(9)).
Fan discharge height: code requires 40 inches minimum above roof surface for hinged upblast fans per § 510.9.1(8)(b). The planned 36 inches is noncompliant.
- Fix: raise the fan or provide an extended duct so the discharge point is ≥ 40 inches above roof surface.
Duct attachment clearance: where the fan attaches to the ductwork, the ductwork must be ≥ 18 inches away from the roof surface per § 510.9.1(8)(a). Verify and adjust supports as necessary.
Grease drain: ensure any low point/trap drains to a noncombustible, closed, rainproof receptacle and does not impede fan operation per § 510.9.1(4–6).
After correcting location (move to 12 ft from intake) and raising discharge to 48 in, the installation would meet the clearances in § 510.9.1 and the hinged upblast‑fan requirements in § 511.1.1.
Related provisions (quick reference)
- § 510.9 — Termination of Type I Hood Exhaust System (general)
- § 510.9.1 — Rooftop Terminations and upblast‑fan clearances (Type I)
- § 510.9.2 — Wall terminations (Type I) and angled intake clearance method/figures
- § 511.1.1 — Upblast fan installation details and drains (fans for commercial cooking)
- § 511.1.3 — Utility set exhaust fans and rooftop fan requirements (references back to § 510.9.1)
- § 502.2.2 — Termination distances for Class 3 air (background on termination distances used by Type II)
- § 519.5 — Termination of Type II Hood Exhaust System (Type II rooftop discharge and moisture‑outlet limits)
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 510.3 High relevance — show source text
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EXHAUST SYSTEMS
on the top portion of the grease duct in accordance with Section 510.3 and shall be labeled at the interior portion of the duct.
510.9 Termination of Type I Hood Exhaust System. The exhaust system shall terminate as follows:
(1) Outside the building with a fan or duct.
(2) Through the roof or to the roof from outside, as in Section 510.9.1, or through a wall, as in Section 510.9.2. [NFPA 96:7.8.1] 510.9.1 Rooftop Terminations. Rooftop terminations shall be arranged with or provided with the following:
(1) A minimum of 10 feet (3048 mm) of horizontal clearance from the outlet to adjacent buildings, property lines, and air intakes.
(2) A minimum of 5 feet (1524 mm) of horizontal clearance from the outlet (fan housing) to any combustible structure.
(3) A vertical separation of 3 feet (914 mm) above any air intakes within 10 feet (3048 mm) of the exhaust outlet.
(4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
(5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
(6) Grease collection systems that meet the requirements of Section 510.9.1(4) and Section 510.9.1(5).
(7) A listed grease duct complying with Section 507.4.7 or ductwork complying with Section 507.4.8.
(8) A hinged upblast fan supplied with flexible weatherproof electrical cable and service hold-open retainer to permit inspection and cleaning that is listed for commercial cooking equipment with the following conditions:
(a) Where the fan attaches to the ductwork, the ductwork is a minimum of 18 inches (457 mm) away from any roof surface, as shown in Figure 510.9.1.
(b) The fan discharges a minimum of 40 inches (1016 mm) away from any roof surface, as shown in Figure 510.9.1.
(9) Other approved fan, provided it meets all of the following criteria:
(a) The fan meets the requirements of Section 510.9.1(3) and Section 511.1.3.
(b) Its discharge or its extended duct discharge meets the requirements of Section 510.9.1(2). (See Section 511.1.3)
(c) Exhaust fan discharge is directed up and away from the roof surface. {NFPA 96:7.8.2.1}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
FIGURE 510.9.1
UPBLAST FAN CLEARANCES
[NFPA 96: FIGURE 7.8.2.1]
510.9.1.1 Listed Vibration Isolation Connec-
CMC § 510.7.6 High relevance — show source text
510.7.6 Listed. For listed grease ducts, see Section 510.4.
510.7.7 Fire Doors. Where openings in the enclosure walls are provided, they shall be protected by listed fire doors of proper rating. Fire doors shall be installed in accordance with NFPA 80. Openings on other listed materials or products shall be clearly identified and labeled according to the terms of the listing and the manufacturer’s instructions and shall be acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.4.1 – 7.7.4.3] The fire door shall be readily accessible, aligned, and of sufficient size to allow access to the rated access
panels on the ductwork. [NFPA 96:7.7.4.4]
510.7.8 Ducts with Enclosure(s). Each duct system shall constitute an individual system serving only exhaust hoods in one fire zone on one floor. Multiple ducts shall not be permitted in a single enclosure unless acceptable to the Authority Having Jurisdiction. [NFPA 96:7.7.5.1 – 7.7.5.2]
510.8 Underground Installations. Grease ducts installed underground shall be approved for underground installation. The material of the grease duct shall be corrosion-resistant and shall comply with Section 510.5.1.
510.8.1 Grease Receptacle. The grease duct shall be sloped to drain the grease back to an approved grease collection device. A grease collection device shall be located at the base of the vertical riser.
510.8.2 Cleanouts. For horizontal installations, cleanouts for cleaning and maintenance shall be provided
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on the top portion of the grease duct in accordance with Section 510.3 and shall be labeled at the interior portion of the duct.
510.9 Termination of Type I Hood Exhaust System. The exhaust system shall terminate as follows:
(1) Outside the building with a fan or duct.
(2) Through the roof or to the roof from outside, as in Section 510.9.1, or through a wall, as in Section 510.9.2. [NFPA 96:7.8.1] 510.9.1 Rooftop Terminations. Rooftop terminations shall be arranged with or provided with the following:
(1) A minimum of 10 feet (3048 mm) of horizontal clearance from the outlet to adjacent buildings, property lines, and air intakes.
(2) A minimum of 5 feet (1524 mm) of horizontal clearance from the outlet (fan housing) to any combustible structure.
(3) A vertical separation of 3 feet (914 mm) above any air intakes within 10 feet (3048 mm) of the exhaust outlet.
(4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
(5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
CMC § 510.9.1 High relevance — show source text
(6) Grease collection systems that meet the requirements of Section 510.9.1(4) and Section 510.9.1(5).
(7) A listed grease duct complying with Section 507.4.7 or ductwork complying with Section 507.4.8.
(8) A hinged upblast fan supplied with flexible weatherproof electrical cable and service hold-open retainer to permit inspection and cleaning that is listed for commercial cooking equipment with the following conditions:
(a) Where the fan attaches to the ductwork, the ductwork is a minimum of 18 inches (457 mm) away from any roof surface, as shown in Figure 510.9.1.
(b) The fan discharges a minimum of 40 inches (1016 mm) away from any roof surface, as shown in Figure 510.9.1.
(9) Other approved fan, provided it meets all of the following criteria:
(a) The fan meets the requirements of Section 510.9.1(3) and Section 511.1.3.
(b) Its discharge or its extended duct discharge meets the requirements of Section 510.9.1(2). (See Section 511.1.3)
(c) Exhaust fan discharge is directed up and away from the roof surface. {NFPA 96:7.8.2.1}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
FIGURE 510.9.1
UPBLAST FAN CLEARANCES
[NFPA 96: FIGURE 7.8.2.1]
510.9.1.1 Listed Vibration Isolation Connec-
tors. Listed vibration isolation connectors shall be permitted to be used on exterior roof locations where required for proper equipment vibration isolation. 510.9.1.2 Inspection and Cleaning. Fans shall be provided with safe access and a work surface for inspection and cleaning. [NFPA 96:7.8.2.2]
510.9.2 Wall Terminations. Wall terminations shall be arranged with or provided with the following properties: (1) The termination shall be through a noncombustible wall with a minimum of 10 feet (3048 mm) of clearance from the outlet to adjacent buildings, property lines, grade level, combustible construction, electrical equipment or lines, and with the closest point of any air intake or operable door or window at or below the plane of the exhaust termination. The closest point of any air intake or operable door or window above the plane of the exhaust termination shall be a minimum of 10 feet (3048 mm) in distance, plus 3 inches (76 mm) for each 1 degree (0.017 rad) from horizontal, the angle of degree being measured from the center of the exhaust termination to the center of the air intake or operable door or window, as indicated in Figure 510.9.2. Exception: A wall termination in a secured area shall be permitted to be at a lower height above grade if acceptable to the Authority Having Jurisdiction. (2) The exhaust flow shall be directed perpendicularly outward from the wall face or upward. (3) All the ductwork shall be pitched to drain the grease back into the hood(s) or with a drain provided to bring the grease back into a container within the building or into a remote grease trap.
CMC § 502.2.4 High relevance — show source text
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CHAPTER 5
EXHAUST SYSTEMS
502.2.4 Commercial Kitchen Ducts. Commercial
kitchens exhaust ducts shall terminate in accordance with
Section 510.9 for Type I exhaust systems or Section 519.5 for Type II exhaust systems.
Part I – Environmental Air Ducts and Product-Conveying Systems.
503.0 Motors, Fans, and Filters.
503.1 General. Motors and fans shall be sized to provide the required air movement. Motors in areas that contain flammable vapors or dusts shall be of a type approved for such environments. A manually operated remote control installed at an approved location shall be provided to shut off fans or blowers in flammable vapor or dust systems. Equipment used in operations that generate explosive or flammable vapors, fumes, or dusts shall be interlocked with the ventilation system so that the equipment cannot be operated unless the ventilation fans are in operation. Motors for fans used to convey flammable vapors or dusts shall be located outside the duct or shall be protected with approved shields and dustproofing. Where belts are used, they shall not enter the duct unless the belt and pulley within the duct are enclosed. Motors and fans shall be accessible for servicing and maintenance.
503.2 Fans. Parts of fans in contact with explosive or flammable vapors, fumes, or dusts shall be of nonferrous or nonsparking materials, or their casing shall be lined or constructed of such material. Where the size and hardness of
materials passing through a fan are capable of producing a spark, both the fan, and the casing shall be of nonsparking materials. Where fans are required to be spark-resistant, their bearings shall not be within the airstream, and parts of the fan shall be grounded. Fans in systems handling materials that are likely to clog the blades, and fans in buffing or woodworking exhaust systems, shall be of the radial-blade or tube-axial type.
Equipment used to exhaust explosive or flammable vapors, fumes, or dusts shall bear an identification plate stating the ventilation rate for which the system was designed.
Fans located in systems conveying corrosives shall be of materials that are resistant to the corrosive or shall be coated
with corrosion-resistant materials.
504.0 Environmental Air Ducts.
504.1 General. Where not specified in this chapter, exhaust ducts shall be constructed and installed in accordance with
Chapter 6 and shall be airtight as approved by the Authority Having Jurisdiction. Environmental air ducts that have an alternate function as a part of an approved smoke control sys
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501.0 General.
501.1 Applicability. This chapter includes requirements for environmental air ducts, product-conveying systems, and commercial hoods and kitchen ventilation. Part I addresses environmental air ducts and product conveying systems. Part II addresses commercial hoods and kitchen ventilation.
502.0 Termination.
502.1 Exhaust Opening Protection. Exhaust openings terminating to the outdoors shall be covered with a corrosionresistant screen having not less than [1] ⁄ 4 of an inch (6.4 mm) openings, and shall have not more than [1] ⁄ 2 of an inch (12.7 mm) openings.
CMC § 510.9. High relevance — show source text
Exception: Type I Hood exhaust termination shall be in accordance with Section 510.9.
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tem in accordance with Section 505.7.3 do not require design as Class 1 product-conveying ducts.
Exceptions:
(1) Ductless range hoods where installed in accordance with the manufacturer’s installation instructions.
(2) Condensing clothes dryers where installed in accordance with the manufacturer’s installation instructions.
504.1.1 Backdraft Protection. Exhaust ducts shall terminate outside the building and shall be equipped with backdraft dampers or with motorized dampers that automatically shut where the systems or spaces served are not in use. [OSHPD 1, 1R, 2, 4 & 5] Exception: Back- draft dampers are not required when the exhaust fan must operate continuously.
Exception: Where the exhaust duct does not discharge into a common exhaust plenum and one of the following:
(1) The exhaust fan runs continuously.
(2) The exhaust duct serves space(s) that are not mechanically heated or cooled.
(3) The space served is maintained at positive pressure. 504.2 Independent Exhaust Systems. Single or combined mechanical exhaust systems for environmental air shall be independent of other exhaust systems. Combined exhaust systems shall operate at negative pressure and shall terminate in accordance with Section 502.2.1. Clothes dryer exhaust systems shall be independent of all other exhaust systems except where permitted in Section 504.4.4. 504.3 Domestic Cooking Exhaust Equipment. Domestic cooking exhaust equipment shall comply with the following requirements, as applicable:
(1) The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall comply with UL 507.
(2) Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.
(3) Domestic cooking appliances with integral downdraft exhaust equipment shall comply with UL 858 or CSA/ANSI Z21.1/CSA 1.1.
(4) Microwave ovens with integral exhaust for installation over the cooking surface shall comply with UL 923.
(5) All domestic kitchen exhaust ducts used in conjunction with domestic range or cooktop hoods shall be constructed of metal and shall have smooth interior surfaces, fastened and sealed with duct mastic or metal tapes that meet the requirements of UL 181A.
Exception: Ducts for domestic kitchen downdraft grillrange ventilation installed under a concrete slab floor shall be permitted to be of approved Schedule 40 PVC provided the following conditions are met:
(1) The under-floor trench in which the duct is installed shall be completely backfilled with sand or gravel.
(2) Not more than 1 inch (25.4 mm) of 6 inch diameter (150 mm) PVC coupling shall be permitted to protrude above the concrete floor surface.
(3) PVC pipe joints shall be solvent cemented to provide an air and greasetight duct.
(4) The duct shall terminate above grade outside the building and shall be equipped with a backdraft damper.
(6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.
CMC § 510.9.2 High relevance — show source text
FIGURE 510.9.2
EXHAUST TERMINATION DISTANCE FROM FRESH AIR INTAKE (FAI) OR OPERABLE DOOR OR WINDOW
[NFPA 96: FIGURE 7.8.3]
511.0 Air Movement.
511.1 Exhaust Fans for Commercial Cooking Opera- tions. Exhaust fans shall be installed in accordance with Section 511.1.1 through Section 511.1.6. Exhaust fans shall comply with UL 705 and be installed in accordance with the manufacturer’s installation instructions.
511.1.1 Upblast Fans. Upblast fans with motors surrounded by the airstream shall be hinged and supplied with flexible weatherproof electrical cable, and service hold-open retainers. Installation shall conform to the requirements of Section 510.9. Upblast fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.2.1 – 8.1.2.3]
511.1.2 In-Line Exhaust Fans. In-line fans shall be of the type with the motor located outside the airstream and with belts and pulleys protected from the airstream by a greasetight housing. In-line fans shall be connected
to the exhaust duct by flanges securely bolted as shown in Figure 511.1.2(1) through Figure 511.1.2(4), or by a system specifically listed for such use. Flexible connectors shall not be used. [NFPA 96:8.1.3.1 – 8.1.3.3]
511.1.2.1 Accessibility. If the design or positioning of the fan allows grease to be trapped, a drain directed to a readily accessible and visible grease receptacle not exceeding 1 gallon (4 L), shall be provided. In-line exhaust fans shall be located in easily accessible areas of adequate size to allow for service or removal. Where the duct system connected to the fan is in an enclosure, the space or room in which the exhaust fan is located shall have the same fire
resistance rating as the enclosure. [NFPA 96:8.1.3.4 – 8.1.3.6]
511.1.3 Utility Set Exhaust Fans. Utility set exhaust fans shall be installed in accordance with Section
511.1.3.1 through Section 511.1.3.3.
511.1.3.1 At the Rooftop. Fans installed at the rooftop termination point shall be in accordance with the following:
(1) Section 510.9.1 and Section 510.9.1.2.
(2) Vibration isolation connectors shall be permitted.
(3) A drain shall be directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L).
511.1.3.2 Within the Building. Fans installed within the building shall be in accordance with the following:
(1) Located in an accessible area of adequate size to allow for service or removal. [NFPA 96:8.1.4.2]
(2) Flexible connectors shall not be used. [NFPA 96:8.1.4.6]
(3) Exhaust fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.4.7]
CMC § 8.1.3.4 High relevance — show source text
resistance rating as the enclosure. [NFPA 96:8.1.3.4 – 8.1.3.6]
511.1.3 Utility Set Exhaust Fans. Utility set exhaust fans shall be installed in accordance with Section
511.1.3.1 through Section 511.1.3.3.
511.1.3.1 At the Rooftop. Fans installed at the rooftop termination point shall be in accordance with the following:
(1) Section 510.9.1 and Section 510.9.1.2.
(2) Vibration isolation connectors shall be permitted.
(3) A drain shall be directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L).
511.1.3.2 Within the Building. Fans installed within the building shall be in accordance with the following:
(1) Located in an accessible area of adequate size to allow for service or removal. [NFPA 96:8.1.4.2]
(2) Flexible connectors shall not be used. [NFPA 96:8.1.4.6]
(3) Exhaust fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.4.7]
511.1.3.3 Duct Systems. Where the duct system connected to the fan is in an enclosure, the space or room in which the exhaust fan is located shall have
the same fire resistance rating as the enclosure. The fan shall be connected to the exhaust duct by flanges securely bolted as shown in Figure 511.1.2(1) through Figure 511.1.2(4) or by a system specifically listed for such use. [NFPA 96:8.1.4.3, 8.1.4.5]
511.1.4 Construction. Exhaust fan housings shall be constructed of carbon steel not less than 0.060 inch (1.524 mm) (No. 16 MSG) in thickness, of stainless steel not less than 0.048 of an inch (1.219 mm) (No. 18 MSG) in thickness, or, if listed, in accordance with the terms of the listing. [NFPA 96:8.1.5]
511.1.5 Openings. Openings for cleaning, servicing, and inspection shall conform to the requirements of Section 510.3.2. Clearances shall conform to the requirements of
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Section 507.4 through Section 507.4.3.3, or Section 510.7.3 and Section 510.7.4 if installed within an enclo sure. [NFPA 96:8.1.6.1, 8.1.6.2] 511.1.6 Standard. All wiring and electrical equipment shall comply with California Electrical Code . [NFPA 96:8.1.7] 511.2 Airflow. The air velocity through a duct shall be not less than 500 feet per minute (ft/min) (2.54 m/s) and not exceed 2500 ft/min (12.7 m/s).
CMC § 504.0 High relevance — show source text
Equipment used to exhaust explosive or flammable vapors, fumes, or dusts shall bear an identification plate stating the ventilation rate for which the system was designed.
Fans located in systems conveying corrosives shall be of materials that are resistant to the corrosive or shall be coated
with corrosion-resistant materials.
504.0 Environmental Air Ducts.
504.1 General. Where not specified in this chapter, exhaust ducts shall be constructed and installed in accordance with
Chapter 6 and shall be airtight as approved by the Authority Having Jurisdiction. Environmental air ducts that have an alternate function as a part of an approved smoke control sys
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501.0 General.
501.1 Applicability. This chapter includes requirements for environmental air ducts, product-conveying systems, and commercial hoods and kitchen ventilation. Part I addresses environmental air ducts and product conveying systems. Part II addresses commercial hoods and kitchen ventilation.
502.0 Termination.
502.1 Exhaust Opening Protection. Exhaust openings terminating to the outdoors shall be covered with a corrosionresistant screen having not less than [1] ⁄ 4 of an inch (6.4 mm) openings, and shall have not more than [1] ⁄ 2 of an inch (12.7 mm) openings.
Exception: Clothes dryers.
502.2 Termination of Exhaust Ducts. Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section
203.0 and classified in Section 403.9.
502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
CMC § 510.3.3 High relevance — show source text
(4) A listed grease duct shall comply with Section 510.3.3 through Section 510.3.7; other ducts shall comply with Section 510.5.
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(5) An approved fan shall meet the requirements of Section 510.9.2(3), and Section 511.1.1 or Section 511.1.3. [NFPA 96:7.8.3] 510.10 Solid-Fuel Duct Systems. Where solid-fuel cooking equipment is to be vented, the duct system shall be in accordance with Section 517.0.
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
Notes:
Fresh air intake (FAI) applies to an air intake, including an operable door or window.
Example: (a) FAIs 1 and 5 are on the same plane of exhaust or lower: 10 feet (3048 mm) min. between closest edges. (b) FAIs 2, 3, and 4 are above plane of exhaust fan: 10 feet + 0.25 feet (3048 mm + 76 mm) per degree between closest edges.
FIGURE 510.9.2
EXHAUST TERMINATION DISTANCE FROM FRESH AIR INTAKE (FAI) OR OPERABLE DOOR OR WINDOW
[NFPA 96: FIGURE 7.8.3]
511.0 Air Movement.
511.1 Exhaust Fans for Commercial Cooking Opera- tions. Exhaust fans shall be installed in accordance with Section 511.1.1 through Section 511.1.6. Exhaust fans shall comply with UL 705 and be installed in accordance with the manufacturer’s installation instructions.
511.1.1 Upblast Fans. Upblast fans with motors surrounded by the airstream shall be hinged and supplied with flexible weatherproof electrical cable, and service hold-open retainers. Installation shall conform to the requirements of Section 510.9. Upblast fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 1 gallon (4 L). [NFPA 96:8.1.2.1 – 8.1.2.3]
511.1.2 In-Line Exhaust Fans. In-line fans shall be of the type with the motor located outside the airstream and with belts and pulleys protected from the airstream by a greasetight housing. In-line fans shall be connected
to the exhaust duct by flanges securely bolted as shown in Figure 511.1.2(1) through Figure 511.1.2(4), or by a system specifically listed for such use. Flexible connectors shall not be used. [NFPA 96:8.1.3.1 – 8.1.3.3]
CMC § 510.9.1.2 High relevance — show source text
tors. Listed vibration isolation connectors shall be permitted to be used on exterior roof locations where required for proper equipment vibration isolation. 510.9.1.2 Inspection and Cleaning. Fans shall be provided with safe access and a work surface for inspection and cleaning. [NFPA 96:7.8.2.2]
510.9.2 Wall Terminations. Wall terminations shall be arranged with or provided with the following properties: (1) The termination shall be through a noncombustible wall with a minimum of 10 feet (3048 mm) of clearance from the outlet to adjacent buildings, property lines, grade level, combustible construction, electrical equipment or lines, and with the closest point of any air intake or operable door or window at or below the plane of the exhaust termination. The closest point of any air intake or operable door or window above the plane of the exhaust termination shall be a minimum of 10 feet (3048 mm) in distance, plus 3 inches (76 mm) for each 1 degree (0.017 rad) from horizontal, the angle of degree being measured from the center of the exhaust termination to the center of the air intake or operable door or window, as indicated in Figure 510.9.2. Exception: A wall termination in a secured area shall be permitted to be at a lower height above grade if acceptable to the Authority Having Jurisdiction. (2) The exhaust flow shall be directed perpendicularly outward from the wall face or upward. (3) All the ductwork shall be pitched to drain the grease back into the hood(s) or with a drain provided to bring the grease back into a container within the building or into a remote grease trap. (4) A listed grease duct shall comply with Section 510.3.3 through Section 510.3.7; other ducts shall comply with Section 510.5.
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EXHAUST SYSTEMS
(5) An approved fan shall meet the requirements of Section 510.9.2(3), and Section 511.1.1 or Section 511.1.3. [NFPA 96:7.8.3] 510.10 Solid-Fuel Duct Systems. Where solid-fuel cooking equipment is to be vented, the duct system shall be in accordance with Section 517.0.
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
Notes:
Fresh air intake (FAI) applies to an air intake, including an operable door or window.
Example: (a) FAIs 1 and 5 are on the same plane of exhaust or lower: 10 feet (3048 mm) min. between closest edges. (b) FAIs 2, 3, and 4 are above plane of exhaust fan: 10 feet + 0.25 feet (3048 mm + 76 mm) per degree between closest edges.
FIGURE 510.9.2
EXHAUST TERMINATION DISTANCE FROM FRESH AIR INTAKE (FAI) OR OPERABLE DOOR OR WINDOW
[NFPA 96: FIGURE 7.8.3]
511.0 Air Movement.
CMC § 802.10.4 Medium relevance — show source text
Connectors. . . . . . . . . . . . . . . 802.10.4, Table 303.10.1,
Table 802.7.3.3
Cooking appliances. . . . . . . . 919.4.1, 919.4.2, 919.5.2,
Draft hoods and controls . . . . . . . . . . . . . . . . . 802.12.6
Ducts, commercial kitchen
exhaust . . . . . . . . . . . . . .303.10.1.1, 507.4, 507.4.2.3,
507.4.6.3, 510.7.3,
510.9.1, 510.9.2
Ducts, furnaces. . . . . . . . . . . . . . . . . . . . . . . . . . . 905.2
Ducts, product conveying,
exhaust. . . . . . . . . . . . . . . . . . . . . 303.10.1.2, 506.10,
Equipment on roofs . . . . . . . . . . . . . . . . 303.8, 303.8.4,
303.8.4.1, 304.2, 304.3.1.1
Fans, commercial
kitchen exhaust . . . . . . . . . . . . . . . . . . . . . . . . 510.7.3
Floor furnace . . . . . . . . . . . . . . . . . . . . . . 906.8, 906.12
Food service appliances. . . . . . . . . . 917.2, 918.0-918.4
Furnaces, central heating . . . . . . . . . . 904.3, 904.4.1.2,
Table 904.3.2
Gas-fired toilets. . . . . . . . . . . . . . . . . . . . . . . . . . . 928.1
Gas fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912.3
Grease removal devices,
commercial kitchen exhaust . . . . . . . . . . 507.4, 507.4.1,
509.2.2.3
Hoods . . . . . . . . . . . . . . . . . . 506.10.2, 507.4-507.4.2.3,
603.13.6
Illuminating appliances . . . 923.1-923.2.1, Table 923.2.1
Infrared heaters. . . . . . . . . . . . . . . . . . . . . . . . . . . 925.3
Kilns . . . . . . . . . . . . . . . . . . . . . . . . . . 603.13.6, 930.5.1
Listed equipment and appliances . . . . . . . . . . . . . 303.1
Piping, fuel gas . . . . . . . . . . . . . . . . . . . . . . . . . D 110.1
CMC § 802.10.1.4 Medium relevance — show source text
TABLE 802.10.1.4 MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES [NFPA 54: TABLE 12.11.2.5] Col2 Col3
VENT CONNECTOR SIZE
VENT CONNECTOR SIZE
VENT CONNECTOR SIZE
DIAMETER
(inches)AREA
(square inches)MINIMUM THICKNESS
(inches)
Up to 14Up to 154 0.053
Over 14 to 16154 to 201 0.067
Over 16 to 18201 to 254 0.093
Over 18Larger than 254 0.123 For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m [2]
802.10.2 Size of Vent Connector. A vent connector for an appliance with a single draft hood or for a Category I fan-assisted combustion system appliance shall be sized and installed in accordance with Section 803.0 or engineering methods. [NFPA 54:12.11.3.1]
For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m [2]
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CHIMNEYS AND VENTS
TABLE 802.8.1
THROUGH-THE-WALL DIRECT VENT TERMINATION CLEARANCES
[NFPA 54: TABLE 12.9.1]
FIGURE
CLEARANCECLEARANCE LOCATION MINIMUM CLEARANCES FOR
DIRECT VENT TERMINALSMINIMUM CLEARANCES
FOR NON-DIRECT VENT
TERMINALSA Clearance above finished grade
level, veranda, porch, deck, or
balcony12 inches 12 inches B Clearance to window or door
that is openable6 inches for Appliances≤ 10 000 Btu/hr
9 inches for Appliances > 10 000 Btu/hrs≤ 50 000 Btu/hr
12 inches for Appliances > 50 000 Btu/hrs≤ 150 000 Btu/hr
Appliances > 150 000 Btu/hr, in accordance with the appliance
manufacturer’s instructions and not less than the clearances
specified for non-direct vent terminals in row B4 feet below or to side
of opening or 1 foot
above openingC Clearance to non-openable win-
dowNone unless otherwise specified by the appliance manufacturer None unless otherwise specified by the appliance manufacturer D Vertical clearance to ventilated
soffit located above the terminal
within a horizontal distance of 2
feet from the center line of the
terminalNone unless otherwise specified by the appliance manufacturer None unless otherwise specified by the appliance manufacturer E Clearance to unventilated soffit None unless otherwise specified by the appliance manufacturer None unless otherwise specified by the appliance manufacturer F Clearance to outside corner California Mechanical Code High relevance — show source text
METAL VENT CONNECTOR DIAMETER –D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)|SINGLE-WALL METAL VENT CONNECTOR DIAMETER –****D (inch)| |||8|8|8|9|9|9|10|10|10| |||APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR|APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)|FAN|FAN|NAT|FAN|FAN|NAT|FAN|FAN|NAT| |VENT
HEIGHT
_H _
(feet)|CONNECTOR
RISE
_R _
(feet)**|Min|Max|Max|Min|Max|Max|Min|Max|Max| |6|1
2
3|292
301
309|366
432
491|200
231
269|362
373
381|474
557
634|252
299
348|499
509
519|594
696
793|316
376
437| |8|1
2
3|313
323
332|407
465
509|207
238
274|387
397
407|530
607
663|263
309
356|529
540
551|672
766
838|331
391
450| |10|1
2CMC § 519.4 Medium relevance — show source text
519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.
519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away
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EXHAUST SYSTEMS
from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.
519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 6 – DUCT SYSTEMS
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Adopting Agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC Adopting Agency BSC BSC-
CGSFM 1 2 1-AC AC ** SS** ** SS/CC** 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6 Adopt Entire Chapter X X X Adopt Entire Chapter as
amended (amended sections
listed below)X X X X X X X X X Adopt only those sections
that are listed belowX Chapter/Section _601.2. CMC § 519.1 Medium relevance — show source text
519.1 Where Required. Type II hoods shall be installed above equipment and dishwashers that generate steam, heat, or products of combustion, and where grease or smoke is not present.
Exceptions:
(1) Dishwashing machines connected to a Type II duct system and exhausted directly to the outdoors.
(2) 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. Such equipment shall be provided with an interlocking device to prevent opening of the appliance prior to completion of its cycle. 519.2 Construction of Type II Hoods. Type II hoods constructed of steel shall be not less than 0.024 of an inch (0.61 mm) (No. 24 gauge). Hoods constructed of copper shall be of copper sheets weighing not less than 0.17 ounces per square inch (oz/in [2] ) (7.47 kg/m [2] ). Joints and seams shall be substantially tight. Solder shall not be used except for sealing a joint or seam. 519.3 Type II Hood Exhaust System Net Airflow. The net airflow for Type II hoods shall be in accordance with Section 508.5.1.5 for light-duty cooking appliances. The net airflow for Type II hoods serving dishwashing appliances shall comply with Section 519.3.1.
519.3.1 Dishwashing Appliances. The net airflow for Type II hoods used for dishwashing equipment shall be not less than 200 cubic feet per minute (0.094 m [3] /s) per linear foot (m) of hood length.
519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.
519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away
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EXHAUST SYSTEMS
from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.
519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 6 – DUCT SYSTEMS
CMC § 101.4.7 Medium relevance — show source text
Existing 101.4.7 Fire walls 706.1 Height (see Height, Building) 502.1, 503, 504, 505, 508, 510 Occupancy classification Chapter 3 Party walls 706.1.1 Relocatable 3113
Replicable Appendix N Building, Existing 202 Building Department 103 Building Official Duties and powers 103, 104 Qualifications Appendix A Records 104.7
Termination A101.4 Building-Integrated Photovoltaic (BIPV) (see Photovoltaic) Built-Up Roof 1507.10 Business Occupancy (Group B) 303.1.1, 303.1.2, 304 Alarms and detection 907.2.2 Ambulatory care facilities 304, 422 Area 503, 505, 506, 507, 508 Height 503, 504, 505, 508, 510 Higher education laboratories 428, 2702.2
Incidental uses 509 Interior finishes Table 803.13, 804 Live load Table 1607.1 Means of egress Aisles 1018.3
Stairway, exit access 1019 Travel distance 1006.3, 1017.2,
1006.2.1
Mixed occupancies 508.2, 508.3, 508.4 Accessory 303.1.2, 508.2 Ambulatory care facilities 422 Assembly 303.1.2
Assembly spaces 1030 Exit signs 1013.1 Guards 1015.2, 1030.17 Main exit 1030.3
Open air 1005.3.1, 1005.3.2, 1006.3, 1009.6.4, 1019.3, 1027, 1030.6.2 Panic hardware 1010.2.8, 1010.4.1 Smoke-protected 1005.3.1, 1005.3.2, 1006.3, 1009.6.4, 1019.3, 1027, 1030.6.2 Travel distance 1006.2.1, 1006.3, 1017.2, 1030.7 Mixed occupancies 508.3, 508.4 Accessory 508.2 Education 303.1.3
CMC § 903.2.7 Medium relevance — show source text
SUSTAINABLE PRACTICES . . . . . . . . . . . . . . .Appendix E SWITCHES, ELECTRICAL SUPPLY LINE . . . . . . .903.2.7
– T –
TANKLESS WATER HEATERS . . . . . . . . . . . . . . . . .1203.3
TERMINATION
Chimneys . . . . . . . . . . . . . . . . . . . . .802.5.4, 802.5.4.2
Environmental air ducts . . . . . . . . . . . . . . . . . . .502.2.1
Exhaust duct systems,
commercial kitchen . . . . . . . . . . . . . . . . .510.9, 519.5
Exhaust
ducts, clothes dryer . . . . . . . . . . . . . . . . . . . . . .504.4 Gas vents . . . . . . . . . . . . . . . . . . . . . . . .802.6, 802.6.1,
802.7.2, 802.8, 802.8.1
Product conveying ducts . . . . . . . . . . . . . . . . . .502.2.3 Type I hood exhaust system . . . . . . . . . . . . . . . . .510.9 Type II hood exhaust system . . . . . . . . . . . . . . . . .519.5
TESTING
Of boilers . . . . . . . . . . . . . . . . . . . . . . . . .1012.1, 1013.0
Of ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .602.2
Of exhaust systems . . . . . . . . . . . . . . . . . . . . . . . .514.0 Of fuel-gas piping . . . . . . . . . . . . . . . . . . .105.3, 1313.0
Of hood assemblies . . . . . . . . . . . . . . . . . . . . . . .508.2
Of insulating materials . . . . . . . . . . . . . .508.3.4, 602.2
Of louvers . . . . . . . . . . . . . . . . . . . . . . .315.1.1, 315.1.2
Of recirculating systems . . . . . . . . . . .516.2.2, 516.2.5,
516.6.4
Of refrigerating equipment . . . . . . . . . . . .105.3, 1114.3,
1116.0
Of safety interlocks . . . . . . . . . . . . . . . . . . . . . . .516.6.4
Required by the Authority
Having Jurisdiction . . . . . . . . . . . . . . . . . . . . .302.2.1
TESTING AGENCY
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.0
Frequently asked questions
Can an upblast fan discharge sideways instead of straight up?
No. For rooftop terminations the exhaust fan discharge must be directed up and away from the roof surface; hinged upblast fans are listed and installed to discharge upward per § 510.9.1(9)(c) and § 511.1.1.
How do I measure the 10‑foot intake clearance for a wall termination?
Measure from the center or closest edge of the exhaust termination to the closest point of the air intake or operable opening. If the intake is above the plane of the exhaust, add 3 inches for each 1 degree of rise as specified for wall terminations in § 510.9.2.
Are grease drains required at rooftop fans?
Yes. Grease traps or low points near the termination must be able to drain into a noncombustible, closed, rainproof container, and rooftop upblast fans must provide a visible, accessible grease receptacle (drain not exceeding 1 gallon for certain fans) as stated in § 510.9.1(4) and § 511.1.1.
Do Type II hood exhausts have the same 10‑ft clearance to intakes as Type I?
Type II terminations reference the general termination distances of Chapter 5 (Section 502.2.2) and add that rooftop terminations be directed away from roof surfaces within 40 inches; check § 502.2.2 and § 519.5 for the applicable distances and limits.
What if I have a listed fan that discharges via an extended duct?
A listed or otherwise approved fan/extended discharge is permitted provided it meets the intake clearances, combustible clearance, and the criteria of § 510.9.1(9) and § 511.1.3. Confirm the extended discharge still meets horizontal/vertical separation to intakes and combustible structures.
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