Sentence 9.32.3.4.(5)

Intent 1:

To limit the probability that outdoor air will not be introduced into the heating system's ducts, which could lead to an inadequate distribution of outdoor air throughout the dwelling unit.

This is to limit the probability of the inadequate control of:

• airborne pollutants,
• oxygen and other components necessary for breathable air, or
• relative humidity, which could lead to condensation, 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:

To limit the probability that outdoor air will only be able to enter the dwelling unit through the building envelope, which could lead to depressurization, which could lead to the spillage of combustion products from fuel-burning appliances that are susceptible to spillage, which could lead to negative effects on the air quality of indoor spaces, which could lead to harm to persons.

Intent 3:

To limit the probability that, on occasion, excessively cold outdoor air will not be adequately mixed with the heating system's return air before it reaches the furnace heat exchanger, which could lead to:

• thermal shock to the heat exchanger, or
• the condensation of combustion gases or water vapour on the heat exchanger.

This is to limit the probability of cracking or premature failure of the heating appliance, which could lead to the leakage of combustion products into living space, which could lead to negative effects on the air quality of indoor spaces, which could lead to harm to persons.