(1) This Section applies to,
(a) rectangular masonry or concrete chimneys not more than 12 m in height serving fireplaces or serving appliances having a combined total rated heat output of 120 kW or less, and
(b) flue pipes serving solid fuel-burning appliances.
(2) Except as provided in Sentence 9.21.1.3. (1), chimneys (other than those described in Sentence (1) and Sentence 9.21.1.2. (1)), gas vents and flue pipes serving gas-, oil- or solid fuel-burning appliances and associated equipment shall conform to Section 6.3.