1. The design, construction and installation of air duct distribution systems serving heating systems in which the rated heat input does not exceed 120 kW shall conform to this Subsection.
2. Air duct distribution systems in which the rated heat input exceeds 120 kW shall conform to Part 6 and Subsection 3.6.5.

1. Except as provided in Sentences (2) to (6) and in 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 similar noncombustible material.
2. Ducts, associated fittings and plenums are permitted to contain combustible material provided they
   1. conform to the appropriate requirements for Class 1 duct materials in CAN/ULC-S110, "Test for Air Ducts,"
   2. conform to Article 3.1.5.18. and Subsection 3.1.9.,
   3. are not used in vertical runs serving more than 2 storeys, and
   4. are not used in air duct systems in which the air temperature may exceed 120°C.
3. Duct sealants shall have a flame-spread rating of not more than 25 and a smoke developed classification of not more than 50.
4. Duct connectors that contain combustible materials and that are used between ducts and air outlet units shall
   1. conform to the appropriate requirements for Class 1 air duct materials in CAN/ULC-S110, "Test for Air Ducts,"
   2. be limited to 4 m in length,
   3. be used only in horizontal runs, and
   4. not penetrate required fire separations.
5. Combustible ducts that are part of a duct system carrying only ventilation air and that are contained entirely within a dwelling unit need not comply with the requirements of Sentences (1) to (4).
6. Except as provided in Sentences 9.33.6.13.(2) and (3), ducts that are part of a return-air duct system and that are contained entirely within a dwelling unit need not comply with the requirements of Sentences (1) to (4).
7. Materials referred to in Sentences (1) to (6), when used in a location where they may be subjected to excessive moisture, shall
   1. have no appreciable loss of strength when wet, and
   2. be corrosion-resistant.

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

1. Coverings, linings and associated adhesives and insulation of air ducts, plenums and other parts of air duct systems shall be of noncombustible material when exposed to heated air or radiation from heat sources that would result in the exposed surface exceeding a temperature of 120°C.
2. Except as provided in Sentence (3), when combustible coverings and linings, including associated adhesives and insulation, are used, they shall have
   1. a flame-spread rating of not more than 25 on any exposed surface or any surface that would be exposed by cutting through the material in any direction, and
   2. a smoke developed classification of 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 are permitted to have
   1. an exposed surface flame-spread rating of not more than 75, and
   2. a smoke developed classification greater than 50.
4. Combustible coverings and linings described in Sentences (2), (3) and (6) shall not flame, glow, smoulder or smoke when tested in accordance with the method of test in ASTM C 411, "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 provided in Sentences (6) and (7), foamed plastic insulation shall not be used as part of an air duct or for insulating an air duct.
6. Foamed plastic insulation conforming to Article 9.25.2.2. is permitted to be used to insulate a galvanized steel, stainless steel or aluminum air duct, provided
   1. the foamed plastic insulation applied to supply ductwork is not less than 3 m from the furnace bonnet,
   2. the temperature within the ductwork where the insulation is installed is not greater than 50°C,
   3. duct joints are taped with a product conforming to Sentence 9.33.6.3.(1),
   4. return air plenums are separated from the foamed plastic insulation, and
   5. the foamed plastic insulation is protected
      1. by one of the interior finishes described in Subsections 9.29.4. to 9.29.9.,
      2. provided the building does not contain a Group C major occupancy, by sheet metal that is mechanically fastened to the supporting assembly independent of the insulation, is not less than 0.38 mm thick and has a melting point of 650°C or more, or
      3. by any thermal barrier that meets the requirements of Clause 3.1.5.15.(2)(e).
7. Foamed plastic insulation is permitted to be used in a ceiling space that acts as a return air plenum provided the foamed plastic insulation is protected from exposure to the plenum in accordance with Sentence 3.1.5.14.(4).
8. Combustible coverings and linings of ducts, including associated adhesives and insulation, shall be interrupted
   1. at the immediate area of operation of heat sources in a duct system, such as electric resistance heaters or fuel-burning heaters or furnaces, and
   2. where the duct penetrates a fire separation.
9. Linings of ducts shall be installed so that they will not interfere with the operation of volume or balancing dampers or of fire dampers, fire stop flaps and other closures.

1. Galvanized steel or aluminum supply ducts shall conform to Table 9.33.6.5.
2. The design of fittings for ducts shall conform to ANSI/SMACNA 006, "HVAC Duct Construction Standards - Metal and Flexible," except that metal thicknesses shall conform to Table 9.33.6.5.

Table 9.33.6.5.
Minimum Metal Thickness of Ducts
Forming Part of Article 9.33.6.5.

1. Where the installation of heating supply ducts in walls and floors creates a space between the duct and construction material, the space shall be fire stopped with noncombustible material at each end.
2. Ducts shall be securely supported by metal hangers, straps, lugs or brackets, except that, where zero clearance is permitted, wooden brackets are permitted to be used.
3. All round duct joints shall be tight-fitting and lapped not less than 25 mm.
4. Rectangular duct connections shall be made with S and drive cleats or equivalent mechanical connections.
5. Duct systems shall have no openings other than those required for the proper operation and maintenance of the system.

1. Air duct systems serving garages shall not be interconnected with other parts of the dwelling unit.
2. Trunk supply ducts shall not be nailed directly to wood members.
3. Branch ducts shall be supported at suitable spacings to maintain alignment and prevent sagging.
4. Ducts passing through unheated spaces shall have all joints taped or otherwise sealed to ensure that the ducts are airtight throughout their length.
5. Combustible ducts in concrete slabs-on-ground that are connected to a furnace supply plenum shall be located not closer than 600 mm to that plenum and not less than 600 mm from its connection to a riser or register.
6. Ducts in or beneath concrete slabs-on-ground shall be watertight and corrosion-, decay-, and mildew-resistant.
7. Underground ducts shall
   1. be constructed to provide interior drainage from and access to all low points, and
   2. not be connected directly to a sewer.

1. The clearance of furnace plenums from combustible material shall conform to the appropriate standards in Sentence 9.33.5.2.(1).
2. Where the plenum clearance required in Sentence (1) is 75 mm or less, the clearance between a supply duct and combustible material shall
   1. be equal to the required plenum clearance within 450 mm of the plenum, and
   2. be not less than 12 mm at a distance of 450 mm or more from the plenum, except that this clearance may 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. (See Note A-3.6.5.6.(2).)
3. Where the plenum clearance required in Sentence (1) is more than 75 mm but not more than 150 mm, the clearance between a supply duct and combustible material shall be
   1. equal to the required plenum clearance within a horizontal distance of 1.8 m of the plenum, and
   2. not less than 12 mm at a horizontal distance of 1.8 m or more from the plenum, except that this distance may be reduced to zero beyond a bend or offset in the duct sufficiently large to shield the remainder of the duct from direct radiation from the furnace heat exchanger. (See Note A-3.6.5.6.(3).)
4. Where the plenum clearance required in Sentence (1) is more than 150 mm, the clearance between a supply duct and combustible material shall be
   1. equal to the required plenum clearance within a horizontal distance of 1 m of the plenum,
   2. not less than 150 mm within a horizontal distance between 1 m and 1.8 m from the plenum, and
   3. not less than 25 mm at a horizontal distance of 1.8 m or more from the plenum, except that this distance may 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. (See Note A-3.6.5.6.(4).)
5. Where 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 in lieu of the clearances listed in Sentences (2), (3) and (4).

1. All branch supply ducts that are not fitted with diffusers with adjustable balance stops shall be supplied with adjustable dampers and fitted with devices to indicate the positions of the dampers.

1. Supply outlets and return openings in the dwelling unit, when located less than 2 m above the floor, shall be protected by grilles having openings of a size that will not allow the passage of a 15 mm diam sphere.
2. Combustible grilles, diffusers and other devices for the supply and return air openings installed in walls and ceilings shall have a flame-spread rating of
   1. not more than 200 in bathrooms, and
   2. not more than 150 in rooms or spaces other than bathrooms.

1. In a dwelling unit, a warm-air supply outlet shall be provided in each finished room that is located adjacent to unheated space.
2. Except as provided in Sentence (3), when a room described in Sentence (1) is located adjacent to exterior walls, such outlet shall be located so as to bathe at least one exterior wall or window with warm air, except in bathrooms, utility rooms or kitchens, where this may not be practical.
3. Where the heating system is also designed to provide ventilation air, ceiling outlets or outlets located high on interior walls are permitted to be installed, provided the outlets are designed for this purpose and are installed with diffusers.
4. At least one warm-air supply outlet shall be provided for each 40 m2 of floor surface area in unfinished basements serving dwelling units, and it shall be located so as to provide adequate distribution of warm air throughout the basement.
5. At least one warm-air supply outlet shall be provided for each 80 m2 of floor surface area in heated crawl spaces serving dwelling units, and it shall be located so as to provide adequate distribution of warm air throughout the crawl space.
6. Except for pipeless furnaces, the capacity of warm-air supply outlets serving dwelling units shall be not less than the design heat loss from the area served and shall not exceed 3 kW per outlet.
7. In basements and heated crawl spaces, the calculated heat gain from the supply ducts and plenum surfaces is permitted to be considered in calculating the design heat loss.
8. The temperature of supply air at warm-air supply outlets shall not exceed 70°C.
9. Warm-air supply outlets located in finished areas shall be provided with diffusers and adjustable openings and shall not be located on a furnace plenum.

1. Return-air inlets shall not be installed in an enclosed room or crawl space that provides combustion air to a furnace.
2. Except for unfinished areas and floor levels which are less than 900 mm above or below an adjacent floor level which is provided with a return-air inlet, at least one return-air inlet shall be provided in each floor level in a dwelling unit.
3. Provision shall be made for the return of air from all rooms by leaving gaps beneath doors, using louvred doors or installing return duct inlets.

1. The return-air system shall be designed to handle the entire air supply.
2. Where any part of a return duct will be exposed to radiation from the furnace heat exchanger or other radiating part within the furnace, such 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
   1. below floor registers,
   2. at the bottom of vertical ducts, and
   3. under furnaces having a bottom return.
5. Spaces between studs or joists used as return ducts shall be separated from the unused portions of such spaces by tight-fitting metal stops or wood blocking.
6. A vertical return duct shall have openings to return air on not more than one floor.
7. The return-air system shall be designed so that the negative pressure from the circulating fan cannot
   1. affect the furnace combustion air supply, nor
   2. draw combustion products from joints or openings in the furnace or flue pipe.

1. Air filters for air duct systems shall conform to the requirements for Class 2 air filter units as described in CAN/ULC-S111, "Fire Tests for Air Filter Units."
2. When electrostatic-type filters are used, they shall be installed so as to ensure that the electric circuit is automatically de-energized when filter access doors are opened or, in dwelling units, when the furnace circulation fan is not operating.
3. When odour removal equipment of the adsorption type is used it shall be
   1. installed to provide access so that adsorption material can be reactivated or renewed, and
   2. protected from dust accumulation by air filters installed on the inlet side.