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9.32.3.8.(4)
ApplicationIntent
OS3OH1
ObjectiveOH1 Indoor Conditions
Attribution
[F81-OH1.1,OH1.2]
Application
Application 1: 
Introduction and minimum temperature of outdoor makeup air for any mechanical air-exhausting device, in dwelling units that:
This applies to self-contained mechanical ventilation 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 9.32.3.8.(2), which exempts the principal ventilation fan operating at a rate not greater than the maximum permitted in Table 9.32.3.3. from the requirements in Article 9.32.3.8. that address the supply of outdoor makeup air to mechanical air exhausting devices,
  • Sentence 9.32.3.8.(8), which exempts dwelling units with solid-fuel-burning appliances from the requirement for outdoor makeup air when all other fuel-fired appliances are direct-vented or mechanically vented and soil gas is not a concern,
  • Sentence 9.32.3.8.(9), which exempts dwelling units from the requirements for outdoor makeup air in Article 9.32.3.8. where a test performed in accordance with the procedures in CAN/CGSB-51.71 indicates that the maximum depressurization levels will not exceed acceptable limits, and
  • 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: 
To limit the probability that occupants will disable outdoor air supply fans, which could lead to excessive negative pressure.
This is to limit the probability of:
  • the ingress of soil gases (such as methane and radon),
  • the spillage of combustion products from fuel-burning appliances that are susceptible to spillage, or
  • moisture ingress from the ground, which could lead to the generation of pollutants from biological growth or from materials that become unstable on wetting.
This is to limit the probability of negative effects on the air quality of indoor spaces, which could lead to harm to persons.
Intent 2: 
[Clause (b)] To limit the probability that outdoor makeup air will be perceived as a draft, which could lead to occupants disabling makeup air fans, which could lead to depressurization, which could lead to negative effects on indoor air quality, which could lead to harm to persons.
Intent 3: 
To exempt mechanical air exhausting devices that are principal ventilation fans operating at a rate not greater than the maximum permitted in Table 9.32.3.3. from the provisions in Article 9.32.3.8. for outdoor makeup air fans, on the basis that Articles 9.32.3.4. and 9.32.3.5. address outdoor makeup air for the principal ventilation fan.
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