The Ontario Building Code | Return-Air System
220.127.116.11. Return-Air System
(1) The return-air system shall be designed to handle the entire air supply.
(2) Except as provided in Sentences (3) and (4), return ductsshall be constructed of material having a surface flame-spread rating of not more than 150.
(3) Where any part of a return duct will be exposed to radiation from the 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.
(4) Return ducts serving solid fuel-fired furnaces shall be constructed of noncombustiblematerial.
(5) Combustible return ducts shall be lined with noncombustible material below floor registers, at the bottom of vertical ducts and under furnaces having a bottom return.
(8) A public corridor shall comply with Sentences 18.104.22.168.(4) and (5).
(9) The return-air system shall be designed so that the negative pressure from the circulating fan cannot affect the furnace combustion air supply nor draw combustion products from joints or openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings in the furnaceor flue pipe.
(10) Return-air from a dwelling unit shall not be recirculated to any other dwelling unit.
Note: On July 1, 2017, Sentence 22.214.171.124.(10) of Division B of the Regulation is amended by striking out "Return-air" at the beginning and substituting "Except as provided in Sentence (14), return-air". (See: O. Reg. 139/17, s. 53 (1))
(11) Except for floor levels that are less than 900 mm above or below an adjacent floor level that is provided with a return-air inlet, at least one return-air inlet shall be provided in each floor level in a dwelling unit.
(13) Return-air inlets shall not be installed in an enclosed room or crawl space that provides combustion air to a furnace.
Note: On July 1, 2017, Article 126.96.36.199. of Division B of the Regulation is amended by adding the following Sentence: (See: O. Reg. 139/17, s. 53 (2))
(14) In a house containing two dwelling units, return-air from one dwelling unit may be recirculated to the other dwelling unit, provided a duct-type smoke detector is installed in the supply or return air duct system serving the entire house which would turn off the fuel supply and electrical power to the heating system upon activation of such detector.