6.2.4.3.

(1) Rectangular panels in plenums and ducts more than 300 mm wide shall be shaped to provide sufficient stiffness.

(2) 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.

(3) Ducts shall be securely supported by metal hangers, straps, lugs or brackets, except that where zero clearance is permitted, wooden brackets may be used.

(4) All round duct joints shall be tight-fitting and lapped not less than 25 mm.

(5) Rectangular duct connections shall be made with S and drive cleats or equivalent mechanical connections.

(6) Trunk supply ducts shall not be nailed directly to wood members.

(7) Branch ducts shall be supported at suitable spacings to maintain alignment and prevent sagging.

(8) 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.

(9) Ducts in or beneath concrete slabs-on-ground shall be watertight, corrosion-, decay- and mildew-resistant.

(10) Where a supply or return duct is not protected by an insulated exterior wall or where the duct is exposed to an unheated space it shall be insulated to provide a thermal resistance of not less than RSI 2.1.

(11) Ductwork passing through unconditioned spaces shall have all joints taped or be otherwise sealed to ensure that the ducts are airtight throughout their length.

(12) Underground ducts shall,

(a) be constructed and installed with a slope to provide interior drainage to all low points,

(b) not be connected directly to a sewer, and

(c) be installed and constructed of materials in conformance with ASHRAE Handbooks, SMACNA Manuals and the HRAI Digest.

(13) A clean-out or pump-out connection shall be provided in an underground duct system at every low point of the duct system.