Chimneys of cupola furnaces, blast furnaces and similar devices
shall extend at least 20 feet above the highest point of any roof
within a radius of 50 feet thereof and be covered on the top with
wire netting or another approved spark-arrester. No woodwork shall
be within three feet of any part of such device or its chimney.
Underground smoke flues shall be covered with at least 12 inches
of solid masonry, or an approved equivalent insulation. If clean-out
openings are installed, they shall be provided with approved double
iron doors or covers, of which the two parts are 12 inches apart,
with the intervening space filled with insulating material. No combustible
flooring shall be laid over any such flues.
All registers used in hot-air furnace heating systems, placed
in any woodwork or incombustible floor, shall rest upon stone or iron
borders firmly set in plaster of paris or gauged mortar. All register
boxes used in any such heating system shall be made of tin plate or
galvanized iron with a flange to fit the rabbet in the border. The
register box shall be enclosed in a tin or galvanized iron casing
turned under the border and spaced at least two inches from the sides
of box. Such casing shall extend from the border to and through the
ceiling below in the case of a floor register and through the partition
in the case of a wall register. When a register box is placed in the
floor over a portable furnace, the space on all sides between the
casing and the register box shall be not less than four inches. Every
hot-air furnace shall have at least one register without a valve or
louvers.
Flues hereafter erected for the removal of foul air or the transmission
of heated air shall be encased in masonry not less than four inches
thick and shall be lined with terra-cotta or other approved incombustible
material. Not more than one gas-burning device shall be direct-connected
with any flue, not shall any such device be connected to any flue
used as a smoke flue.