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3.634 articles · 5 subsections

Service Facilities

3.6.1

General

3.6.1.1

Scope

(1)The provisions of this Section apply to horizontal service spaces, vertical service spaces, attic or roof spaces, ducts, crawl spaces, shaft spaces, service rooms, and mechanical penthouses, and facilities contained therein.

3.6.1.2

Reserved

3.6.1.3

Reserved

3.6.1.4

Storage Use Prohibition

(1)Service spaces shall not be designed to facilitate subsequent use as storage space.

3.6.1.5

Appliances Installed Outside a Building

(1)A fuel-fired appliance installed on the roof of a building or in another location outside the building shall be installed not less than

  • (a) 1.2 m from a property line, measured horizontally, and
  • (b) 3 m from an adjacent wall of the same building if that wall contains any opening within 3 storeys above and 5 m horizontally from the appliance, unless every opening within these limits is protected by (i) a closure having a fire-protection rating not less than 45 min determined in accordance with Article 3.1.8.4., or (ii) a wired glass assembly permitted for use in a vertical fire separation and described in Article 2.3.15. of MMAH Supplementary Standard SB-2, "Fire Performance Ratings."
3.6.1.6

Fixed Access Ladders

(1)If a fixed ladder is installed to provide access to a roof of a building, the design and installation of the attachment and anchorage system for the ladder shall be as described in MMAH Supplementary Standard SB-8, "Design, Construction and Installation of Anchorage System for Fixed Access Ladders."

3.6.2

Service Rooms

3.6.2.1

Fire Separations Around Service Rooms

(1)Except as permitted by Sentences (2), (8), (9) and (10), fuel-fired appliances shall be installed in service rooms separated from the remainder of the building by fire separations having a fire-resistance rating not less than 1 h.

(2)Except as required by Sentence (3), a fuel-fired appliance that serves only one room or suite is not required to be installed in a service room separated from the remainder of the building.

(3)A solid-fuel-burning appliance shall not be located in a repair garage, a storage garage, or any other location where it could be exposed to flammable vapours or gases unless

  • (a) it is enclosed in a service room that is separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 1 h,
  • (b) it is supplied with combustion air directly from outside the building, and
  • (c) the heat that it generates is supplied indirectly to the space served by means of ducts or piping.

(4)A service room containing an incinerator shall be separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 2 h.

(5)Equipment that uses a liquid having a flash point below 93.3°C shall be installed in a service room separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 1 h.

(6)Electrical equipment that is required to be located in a service room by a regulation made under the Electricity Act, 1998, shall be installed in a service room separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 1 h.

(7)Except as permitted by Sentence (8), in a storey that is not sprinklered throughout, a service room that contains service equipment other than that addressed by Sentences (1) to (6), shall be separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 1 h.

(8)Where a service room contains a limited quantity of service equipment, and the service equipment neither constitutes a fire hazard nor is essential to the operation of fire safety systems in the building, the requirements for a fire separation shall not apply.

(9)A fire separation is not required between a fireplace and the space it serves.

(10)A fire separation is not required between a rooftop appliance and the building it serves.

(11)The fire separation provisions for a fuel-fired appliance in a portable classroom shall conform to Article 3.9.3.7.

3.6.2.2

Service Rooms Under Exits

(1)A service room containing service equipment subject to possible explosion, such as boilers operating in excess of 100 kPa (gauge) and some types of refrigerating machinery and transformers, shall not be located directly under a required exit.

3.6.2.3

Service Equipment

(1)A service room containing space heating, space cooling and service water heating appliances is permitted to contain other service equipment such as electrical service equipment.

3.6.2.4

Incinerator Rooms

(1)A service room containing an incinerator shall not contain other fuel-fired appliances.

3.6.2.5

Storage of Combustible Refuse and Recycling

(1)Except as required by Sentence 3.6.3.3.(9), a room for the temporary storage of combustible refuse and materials for recycling shall be

  • (a) separated from the remainder of the building by a fire separation with a fire-resistance rating not less than 1 h, except that a fire separation with a fire-resistance rating not less than 45 min is permitted where the fire-resistance rating of the floor assembly is not required to exceed 45 min, and
  • (b) sprinklered.
3.6.2.6

Door Swing for Service Rooms

(1)A swing-type door from a service room containing a boiler or incinerator shall swing outward from the room, except that the door shall swing inward if the door opens onto a corridor or any room used for an assembly occupancy.

3.6.2.7

Electrical Equipment Vaults

(1)Where an electrical equipment vault is required by the Electrical Safety Code adopted under Ontario Regulation 164/99 (Electrical Safety Code) made under the Electricity Act, 1998, the electrical equipment vault shall be totally enclosed by a fire separation of solid masonry or concrete construction having a fire-resistance rating of not less than 3 h if the vault is not provided with an automatic fire extinguishing system and not less than 2 h if the vault is so protected.

(2)Where a building is required to be sprinklered throughout, the electrical equipment vault described in Sentence (1) need not be sprinklered provided

  • (a) the vault is designed for no purpose other than to contain the electrical equipment, and
  • (b) a smoke detector is provided in the vault that will actuate the building fire alarm system in the event of a fire in the vault.

(3)A vault, that is part of a building and houses electrical equipment indoors, shall have

  • (a) roofs or ceilings consisting of reinforced concrete of adequate strength for the conditions and not less than 150 mm thick, and
  • (b) floors consisting of reinforced concrete of adequate strength for the conditions and not less than 150 mm thick, except that floors that are at excavation level are permitted to be of reinforced concrete not less than 100 mm thick.

(4)Walls, roofs or ceilings, and floors shall be adequately anchored together in a manner designed to resist dislodgement by explosion.

(5)Only pipes or ducts necessary for fire protection or the proper operation of the electrical installation shall penetrate the fire separations surrounding the electrical equipment vault.

(6)A ventilation duct or opening, that penetrates the fire separation to the outdoors, need not be protected by a closure at the penetration.

(7)Each door to an electrical equipment vault shall be provided with a substantial lock or padlock.

(8)Explosion-relief devices and vents or other protective measures shall be provided for every electrical equipment vault containing dielectric liquid-filled electrical equipment in conformance with Sentence 3.3.1.21.(3).

(9)Every electrical equipment vault shall be provided with a ventilation system designed in conformance with Part 6 to prevent the ambient temperature in the vault from exceeding 40°C.

(10)Where the vault ventilation system in Sentence (9) is directly from an outdoor area by natural ventilation without the use of ducts, and where the electrical equipment is the principal source of heat, the combined net area of inlet and outlet openings shall be not less than 0.002 m2/kVa of electrical equipment capacity with a minimum of 0.093 m2, except that

  • (a) where equipment in the power class as described in CAN/CSA-C88-M, "Power Transformers and Reactors" is installed, ventilation requirements are permitted to be based on the actual full-load losses, or
  • (b) where the equipment is installed for emergency purposes only and is not normally energized, it need not be considered in determining the ventilation requirements.

(11)In the vault ventilation system in Sentence (10), the inlet for fresh air shall lead from an outdoor area and shall terminate at a point not more than 1 000 mm above the floor level of the vault.

(12)Where the vault ventilation system in Sentence (9) is a mechanical system, it shall be separate from the system for the remainder of the building and shall be designed so that

  • (a) the vault temperature is thermostatically controlled,
  • (b) the fan is located so that it may be serviced without danger to personnel,
  • (c) a high temperature alarm is provided in the vault,
  • (d) the system is automatically shut off in the event of a fire in the vault, and
  • (e) a filter is provided in the air inlet if there is a possibility of dirt being drawn in.

(13)All ventilation openings shall be protected in conformance with Sentences 6.3.2.9.(4) and (5) and the protection shall be installed in such a manner that it cannot be removed from the outside by the use of common tools and it is tamperproof.

(14)Except as permitted in Sentence (15), the floor of an electrical equipment vault referred to in Sentences (1) and (2) shall be liquid tight and surrounded by liquid tight walls and sills of sufficient height to confine within the vault all of the liquid from the largest item of electrical equipment, but to a height of not less than 100 mm.

(15)The floor of the electrical equipment vault described in Sentences (1) and (2) may be provided with a floor drain connected to a covered sump capable of holding all of the liquid from the largest item of electrical equipment, and the connection shall have a noncombustible trap to prevent the spread of fire from the vault to the sump.

(16)Where the electrical equipment vault is located in a hazardous location classified as Class II, Division 1 in under the Electricity Act, 1998, it shall have

  • (a) no vent opening except to the exterior of the building, and
  • (b) suitable pressure-relief openings communicating only with the air outside the building.

(17)Where doors are provided between the vault described in Sentence (16) and the rest of the building, they shall have suitable seals such as weatherstripping to minimize the entrance of dust into the vault.

(18)Every electrical equipment vault shall be provided with

  • (a) adequate lighting, controlled by one or more switches located near the entrance,
  • (b) luminaires located so that they may be relamped without danger to personnel, and
  • (c) a grounded receptacle located in a convenient location inside the vault, near the entrance.
3.6.2.8

Emergency Power Installations

(1)Where a generator intended to supply emergency power for lighting, fire safety and life safety systems is located in a building, except where such building is used solely for the purpose of housing the generator and its ancillary equipment, it shall be located in a room that

  • (a) is separated from the remainder of the building by a fire separation with a fire-resistance rating not less than 2 h, and
  • (b) contains only the generating set and equipment that is related to the emergency power supply system.
3.6.2.9

Storage of Oxygen Containers

(1)In a Group B, Division 2 or 3 occupancy or in a retirement home, a room for the storage of oxygen containers shall be

  • (a) separated from the remainder of the building by a fire separation having a fire-resistance rating not less than 1 h,
  • (b) designed for the storage of oxygen containers only,
  • (c) vapour tight,
  • (d) lined with noncombustible finish,
  • (e) separately exhausted to the exterior, and
  • (f) equipped with racks to store the containers.
3.6.3

Vertical Service Spaces and Service Facilities

3.6.3.1

Fire Separations for Vertical Service Spaces

(1)Except as provided in Articles 3.6.3.3. and 3.6.3.5. and Section 3.5., a vertical service space shall be separated from all other portions of each adjacent storey by a fire separation having a fire-resistance rating conforming to Table 3.6.3.1. for the fire-resistance rating required by Subsection 3.2.2. for

  • (a) the floor assembly above the storey, or
  • (b) the floor assembly below the storey, if there is no floor assembly above.

(2)A vertical service space that does not extend through the roof of a building shall be enclosed at the top with construction having a fire-resistance rating not less than that required for the vertical service space walls.

(3)A vertical service space that does not extend to the bottom of a building shall be enclosed at the lowest level with construction having a fire-resistance rating not less than that required for the vertical service space walls.

(4)A vent from a vertical service space not extending to the roof shall be enclosed within the building with construction having a fire-resistance rating not less than that required for the vertical service space walls.

(5)Only openings that are necessary for the use of the vertical service space shall be permitted through a vertical service space enclosure.

Table 3.6.3.1Fire Separations for Vertical Service Space
Fire-Resistance Rating of Fire Separation Required for Floor AssemblyMinimum Fire-Resistance Rating of Vertical Service Space
less than 45 min---
45 min45 min
1 h45 min
1.5 h1 h
2 h or more1 h
3.6.3.2

Foamed Plastic Protection

(1)Foamed plastic insulation in a vertical service space shall be protected in conformance with Article 3.1.5.15.

3.6.3.3

Linen and Refuse Chutes

(1)A linen chute or refuse chute shall

  • (a) be impervious to moisture,
  • (b) have a smooth internal surface,
  • (c) be corrosion-resistant,
  • (d) be constructed of noncombustible material, and
  • (e) be located in a shaft in which there are no services other than noncombustible drain, waste and vent piping or noncombustible water piping.

(2)A shaft containing a linen chute or refuse chute shall have a fire-resistance rating conforming to Sentence 3.6.3.1.(1), but not less than

  • (a) 1 h if the chute outlet for the discharge room is protected by an automatic, self-latching closure held open by a fusible link, or
  • (b) 2 h if no closure is provided at the chute outlet into the discharge room.

(3)An interior linen chute or refuse chute shall extend not less than 1 m above the roof and shall be vented above the roof with a vent which

  • (a) has an unobstructed area not less than the cross-sectional area of the chute, and
  • (b) is equipped with a cover that will open automatically, or that can be opened manually, in the event of a fire in the chute.

(4)Intake openings for a linen chute or a refuse chute shall

  • (a) have an area not more than 60% of the cross-sectional area of the chute, and
  • (b) be fitted with closures designed to close automatically and latch after use.

(5)Intake openings for a linen chute or a refuse chute shall be located in rooms or compartments that

  • (a) have no dimension less than 750 mm,
  • (b) are separated from the remainder of the building by a fire separation with a fire-resistance rating not less than 45 min,
  • (c) are designed for no other purpose, and
  • (d) do not open directly into an exit.

(6)Sprinklers shall be installed at the top of each linen chute or refuse chute, at alternate floor levels and in the room or bin into which the chute discharges.

(7)The room into which a linen chute discharges shall be separated from the remainder of the building by a fire separation with a fire-resistance rating not less than 1 h.

(8)A refuse chute shall be equipped at the top with spray equipment for washing-down purposes.

(9)A refuse chute shall discharge only into a room or bin separated from the remainder of the building by a fire separation with a fire-resistance rating not less than 2 h.

(10)The room or bin into which a refuse chute discharges shall be of sufficient size to contain the refuse between normal intervals of emptying, be impervious to moisture and be equipped with a water connection and floor drain for washing-down purposes.

(11)A room into which a refuse chute discharges shall contain no service equipment that is not related to refuse handling and disposal.

3.6.3.4

Exhaust Duct Negative Pressure

(1)If a vertical service space contains an exhaust duct that serves more than one fire compartment, the duct shall have a fan located at or near the exhaust outlet to ensure that the duct is under negative pressure.

3.6.3.5

Grease Duct Enclosures

(1)Except as provided in Sentence (2), fire separations enclosing grease ducts for commercial cooking operations shall conform to NFPA 96, "Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations."

(2)The fire-resistance rating of field-applied and factory-built grease duct enclosure assemblies shall be determined in conformance with CAN/ULC-S144, "Standard Method of Fire Resistance Test - Grease Duct Assemblies."

3.6.4

Horizontal Service Spaces and Service Facilities

3.6.4.1

Scope

(1)This Subsection applies to horizontal service spaces and service facilities, including ceiling spaces, duct spaces, crawl spaces and attic or roof spaces.

3.6.4.2

Fire Separations for Horizontal Service Spaces

(1)Except as provided in Article 3.6.3.5., a horizontal service space that penetrates a required vertical fire separation shall be separated from the remainder of the building it serves in conformance with Sentence (2).

(2)If a horizontal service space or other concealed space is located above a required vertical fire separation other than a vertical shaft, this space need not be divided at the fire separation as required by Article 3.1.8.3. provided the construction between this space and the space below is a fire separation with a fire-resistance rating equivalent to that required for the vertical fire separation, except that the fire-resistance rating is permitted to be not less than 30 min if the vertical fire separation is not required to have a fire-resistance rating more than 45 min.

3.6.4.3

Plenum Requirements

(1)A concealed space used as a plenum within a floor assembly or within a roof assembly need not conform to Sentence 3.1.5.18.(1) and Article 3.6.5.1. provided

  • (a) all materials within the concealed space have a flame-spread rating not more than 25 and a smoke developed classification not more than 50, except for (i) tubing for pneumatic controls, (ii) optical fibre cables and electrical wires and cables with combustible insulation, jackets or sheathes that are used for the transmission of voice, sound or data and conform to Sentences 3.1.4.3.(2) and 3.1.5.21.(2), (iii) totally enclosed non-metallic raceways with an FT6 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings required to be of noncombustible construction or in buildings or parts of buildings permitted to be of encapsulated mass timber construction, and (iv) totally enclosed non-metallic raceways with an FT4 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings permitted to be of combustible construction, and,
  • (b) the supports for the ceiling membrane are of noncombustible material having a melting point not below 760°C.

(2)If a concealed space referred to in Sentence (1) is used as a return-air plenum and incorporates a ceiling membrane that forms part of the required fire-resistance rating of the assembly, every opening through the membrane shall be protected by a fire stop flap that

  • (a) stops the flow of air into the concealed space in the event of a fire,
  • (b) is supported in a manner that will maintain the integrity of the ceiling membrane for the duration of time required to provide the required fire-resistance rating,
  • (c) conforms to CAN/ULC-S112.2, "Standard Method Fire Test of Ceiling Firestop Flap Assemblies," and
  • (d) activates at a temperature approximately 30°C above the normal maximum temperature that occurs in the return-air plenum, whether the air duct system is operating or shut down.
3.6.4.4

Attic or Roof Space Access

(1)An attic or roof space more than 600 mm high shall be provided with access from the floor immediately below by a hatchway not less than 550 mm by 900 mm or by a stairway.

3.6.4.5

Horizontal Service Space Access

(1)A horizontal service space, consisting of ceiling and duct spaces, that is more than 1 200 mm high and 600 mm wide shall have inspection doors not less than 300 mm in both horizontal and vertical dimensions placed so that the entire interior of the duct or space can be viewed.

3.6.4.6

Crawl Space Access

(1)A crawl space shall have at least one access opening not less than 550 mm by 900 mm.

3.6.5

Air Duct and Plenum Systems

3.6.5.1

Duct Materials

(1)Except as permitted by Sentences (2) to (5) and Article 3.6.4.3., all ducts, duct connectors, associated fittings and plenums used in air duct systems shall be constructed of steel, aluminum alloy, copper, clay or other noncombustible material.

(2)Except as permitted by Sentence (3), ducts, associated fittings and plenums are permitted to contain combustible material provided they

  • (a) conform to the appropriate requirements for Class 1 duct materials in CAN/ULC-S110, "Standard Methods of Test for Air Ducts,"
  • (b) conform to Article 3.1.5.18. in a building required to be of noncombustible construction or in a building or part of a building permitted to be of encapsulated mass timber construction,
  • (c) conform to Subsection 3.1.9.,
  • (d) are used only in horizontal runs in a building required to be of noncombustible construction or in a building or part of a building permitted to be of encapsulated mass timber construction,
  • (e) are not used in vertical runs serving more than 2 storeys in a building permitted to be of combustible construction, and
  • (f) are not used in air duct systems in which the air temperature could be more than 120°C.

(3)Combustible ducts which are part of a duct system conveying only ventilation air and are contained entirely within a dwelling unit need not comply with the requirements of Sentences (1) and (2).

(4)Duct sealants shall have a flame-spread rating not more than 25 and a smoke developed classification not more than 50.

(5)Duct connectors that contain combustible materials and that are used between ducts and air outlet units shall

  • (a) conform to the appropriate requirements for Class 1 air duct materials in CAN/ULC-S110, "Standard Methods of Test for Air Ducts,"
  • (b) be not more than 4 m long,
  • (c) be used only in horizontal runs, and
  • (d) not penetrate a required fire separation.
3.6.5.2

Vibration Isolation Connectors

(1)Except as permitted by Sentence (2), vibration isolation connectors in air duct systems shall be noncombustible.

(2)Combustible fabric vibration isolation connectors are permitted provided they

  • (a) are not more than 250 mm long,
  • (b) comply with the flame-resistance requirements of CAN/ULC-S109, "Standard Method for Flame Tests of Flame-Resistant Fabrics and Films," and
  • (c) are not used in a location where they are exposed to heated air or radiation from heat sources that could cause the exposed surface temperature to be more than 120°C.
3.6.5.3

Tape

(1)Tape used to seal joints in air ducts, plenums and other parts of air duct systems shall meet the flame-resistance requirements for fabric in CAN/ULC-S109, "Standard Method for Flame Tests of Flame-Resistant Fabrics and Films."

3.6.5.4

Coverings, Linings, Adhesives and Insulation

(1)Coverings, linings and associated adhesives and insulation for air ducts, plenums and other parts of air duct systems that would have an exposed surface temperature more than 120°C when exposed to heated air or radiation from heat sources shall be of noncombustible material.

(2)Except as permitted by Sentence (3), combustible coverings and linings, including associated adhesives and insulation, shall have

  • (a) a flame-spread rating not more than 25 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, and
  • (b) a smoke developed classification not more than 50.

(3)The outer covering of ducts, plenums and other parts of air duct systems used within an assembly of combustible construction is permitted to have

  • (a) an exposed surface flame-spread rating not more than 75, and
  • (b) a smoke developed classification not more than 50.

(4)Combustible coverings and linings referred to in Sentences (2) and (3) shall not flame, glow, smoulder or smoke when tested in accordance with the method of test in ASTM C411, "Standard Specification for Hot-Surface Performance of High-Temperature Thermal Insulation," at the maximum temperature to which the coverings and linings are to be exposed in service.

(5)Except as permitted by Sentence (6), foamed plastic insulation shall not be used as part of an air duct system or for insulating an air duct.

(6)Foamed plastic insulation is permitted to be installed in a ceiling space that is used as a return air plenum provided the foamed plastic insulation is protected from exposure to the plenum in accordance with Article 3.1.5.15.

(7)Combustible coverings and linings of ducts, including associated adhesives and insulation, shall be interrupted where the duct penetrates a fire separation and at the immediate area of operation of heat sources in a duct system, including electric resistance heaters or fuel-burning heaters or furnaces.

3.6.5.5

Insulation and Coverings

(1)Insulation and coverings on pipes in which the temperature of the fluid exceeds 120°C shall

  • (a) be made of noncombustible material, or
  • (b) not flame, glow, smoulder or smoke when tested in accordance with ASTM C411, "Standard Specification for Hot-Surface Performance of High-Temperature Thermal Insulation," at the maximum temperature to which the insulation or covering is to be exposed in service.

(2)Except as permitted by Sentence (5), where combustible insulation is used on piping in a horizontal service space or a vertical service space, the insulation and coverings on that piping shall have a flame-spread rating, on any exposed surface and on any surface that would be exposed by cutting through the material in any direction,

  • (a) not more than 25 in a building required to be of noncombustible construction or in a building or part of a building permitted to be of encapsulated mass timber construction, or
  • (b) not more than 75 in a building permitted to be of combustible construction.

(3)Except as permitted by Sentence (5), insulation and coverings on piping located in rooms and spaces other than the service spaces described in Sentence (2) shall have a flame-spread rating not more than that required for the interior finish of the ceiling of the room or space.

(4)Except as permitted by Sentence (5), combustible insulation and covering used on piping in a building within the scope of Subsection 3.2.6. shall have a smoke developed classification not more than 100.

(5)No flame-spread rating or smoke developed classification limits are required for combustible insulation and coverings used on piping located within a

  • (a) concealed space in a wall,
  • (b) floor slab, or
  • (c) noncombustible enclosure.
3.6.5.6

Clearance of Ducts and Plenums

(1)The clearance of furnace plenums from combustible material shall conform to the requirements of the appropriate standards referenced in Sentence 6.2.1.5.(1).

(2)If the plenum clearance required in accordance with Sentence (1) is not more than 75 mm, the clearance between a supply duct and combustible material shall be not less than

  • (a) the required plenum clearance within a horizontal distance of 450 mm from the plenum, and
  • (b) 12 mm at a horizontal distance of 450 mm or more from the plenum, except that this clearance is permitted to be reduced to zero beyond a bend or offset in the duct sufficiently large to shield the remainder of the supply duct from direct radiation from the furnace heat exchanger.

(3)If the plenum clearance required in accordance with Sentence (1) is more than 75 mm but not more than 150 mm, the clearance between a supply duct and combustible material shall be not less than

  • (a) the required plenum clearance within a horizontal distance of 1 800 mm from the plenum, and
  • (b) 12 mm at a horizontal distance of 1 800 mm or more from the plenum, except that this distance is permitted to be reduced to zero beyond a bend or offset in the duct sufficiently large to shield the remainder of the supply duct from direct radiation from the furnace heat exchanger.

(4)If the plenum clearance required in accordance with Sentence (1) is more than 150 mm, the clearance between a supply duct and combustible material shall be not less than

  • (a) the required plenum clearance within a horizontal distance of 1 000 mm from the plenum,
  • (b) 150 mm within a horizontal distance between 1 000 mm and 1 800 mm from the plenum, and
  • (c) 25 mm at a horizontal distance of 1 800 mm or more from the plenum, except that this distance is permitted to be reduced to 8 mm beyond a bend or offset in the duct sufficiently large to shield the remainder of the supply duct from direct radiation from the furnace heat exchanger.

(5)If a register is installed in a floor directly over a pipeless furnace, a double-walled register box with not less than 100 mm between walls, or a register box with the warm-air passage completely surrounded by the cold-air passage, shall be permitted instead of the clearances listed in Sentences (2) to (4).

3.6.5.7

Supply, Return, Intake and Exhaust-Air Openings

(1)Combustible grilles, diffusers and other devices for supply, return, and exhaust-air openings in rooms shall conform to the flame-spread rating and smoke developed classification requirements for the interior finish of the surface on which they are installed.

3.6.5.8

Return-Air System

(1)Except as required by Sentences (2) and (3), return ducts shall be constructed of material having a flame-spread rating not more than 150.

(2)If any part of a return duct will be exposed to radiation from the furnace heat exchanger or other radiating part within the furnace, that part of a return duct directly above or within 600 mm of the outside furnace casing shall be noncombustible.

(3)Return ducts serving solid-fuel-burning furnaces shall be constructed of noncombustible material.

(4)Combustible return ducts shall be lined with noncombustible material

  • (a) below floor registers,
  • (b) at the bottom of vertical ducts, and
  • (c) under furnaces having a bottom return.