Code Library › Volume 1 › Section 3.6 — Service Facilities
PART 3 — FIRE PROTECTION, OCCUPANT SAFETY AND ACCESSIBILITYUpdated for the 2024 Ontario Building Code

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.
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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.