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9.32.3.4.(5)
ApplicationIntent
OH1OS3
ObjectiveOS3 Safety in Use
Attribution
(a) [F43,F50,F53-OS3.4]
(b) [F43,F50,F81-OS3.4]
Application
Application 1: 
Installation and connection of outdoor air supply ducts between the furnace and the outdoors, in self-contained heating-season mechanical ventilation systems coupled to forced air heating systems serving single dwelling units with 5 or fewer bedrooms that are supplied with electrical power and a heating system, in buildings to which:
  • Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], or
  • Part 6 applies [see Sentence 1.3.3.2.(1) of Division A for application of Part 6 and Sentence 6.2.2.1.(3)].
Exceptions: 
except as stated in Sentence 9.32.3.1.(1), which applies to heating-season mechanical ventilation systems designed to comply with CAN/CSA-F326-M.
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Intent
Intent 1: 
[Clause (a)] To limit the probability of the inadequate replacement of indoor air with outdoor air, which could lead to the excessive depressurization of dwelling units by exhaust fans, which could lead to the spillage of combustion products from fuel-burning appliances that are susceptible to spillage.
This is to limit the probability of the entry of carbon monoxide gas into living space, which could lead to the acute poisoning or asphyxiation of persons.
Intent 2: 
[Clauses (a) and (b)] To limit the probability of the inadequate mixing of indoor air with return air, which could lead to untempered outdoor air passing over the furnace heat exchanger, which could lead to:
  • thermal shock to the heat exchanger, or
  • the condensation of combustion gases or water vapour.
This is to limit the probability of cracking or premature failure of the heat exchanger, which could lead to the leakage of carbon monoxide gas into living space, which could lead to the acute poisoning or asphyxiation of persons.
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