Osburn OB01801 - Manual (Page 8)

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2.2 Installation instructions
Inspect the masonry fireplace according to the safety information and fireplace requirements and have it
cleaned and/or upgraded as necessary.
2.3 Compliance of the masonry fireplace
Where the masonry fireplace opening is 6 ft
2
(0.56 m
2
) or larger, the hearth extension shall extend at
least 20'' (508 mm) in front of the facing material and at least 12'' (305 mm) beyond each side of the
fireplace opening. Where the masonry fireplace opening is less than 6 ft
2
(0.56 m
2
), the hearth extension
shall extend at least 16'' (406 mm) in front of the facing material and at least 8'' (203 mm) beyond each
side of the fireplace opening.
Note that if you must modify the hearth extension to comply with these measures, depending on the size
of the masonry fireplace opening, the hearth extension must have a minimum of
4'' (102 mm ) thick (see Figure 2.6a and 2.6b.)