To limit the probability that combustion products will spill from one or more appliances into living space, which could lead to negative effects on the air quality of indoor spaces, which could lead to harm to persons.
To exempt constructions from the application of Sentence 9.21.2.1.(1), where an adequate draft is maintained for each appliance and the installation of flue pipes conforms to Sentences 9.21.2.2.(2) and (3).