7(1)Subject to sub-paragraph (2) below, section 14 (height of chimneys for furnaces) does not apply to any furnace served by a chimney the construction of which was begun or the plans for which were passed before 1st April 1969 (which was the day appointed for the coming into force of the enactments replaced by section 14).E+W+S
(2)Notwithstanding sub-paragraph (1), section 14 does apply to—
(a)any furnace the combustion space of which has been increased on or after 1st April 1969; or
(b)any furnace the installation of which was begun on or after that day and which replaces a furnace which had a smaller combustion space.