Sentence 9.32.3.4.(2)

Intent 1:

To limit the probability of the occasional excessive flow of cold outdoor air through the furnace under wind pressure.

This is to limit the probability of:

• thermal shock to heat exchangers, or
• condensation of combustion gases or water vapour.

This is to limit the probability of cracking, corrosion, or premature failure of the heating appliance, which could lead to the leakage of carbon monoxide gas into living space, which could lead to the acute poisoning or asphyxiation of persons.

Intent 2:

[Clause 9.32.3.4.(2)(b)] Where the normal operating exhaust capacity of the principal ventilation fan exceeds the maximum permitted outdoor airflow, and the system does not incorporate means for tempering outdoor air, to direct Code users to Clause 9.32.3.1.(1)(a) or Article 9.32.3.5.