Sentence 9.32.3.4.(5)

Intent 1:

[Clause 9.32.3.4.(5)(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 9.32.3.4.(5)(a) and 9.32.3.4.(5)(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.