Heatilator BIR50 Owner's Manual page 43

2 x 4 stud header
Standoffs
Notches
Non-combustible
Decorative Facing
such as:
Steel, iron, brick,
tile, concrete, slate,
glass, plasters.
of ANSI/NFPA211.
Combustible Wall & Decorative Facing
12 in./305 mm
Mantel
Grid represents
1 in. squares
6 in./152 mm
minimum
1 1/2 in./38 mm
maximum
Measured from top of fireplace opening
Seal joint with
non-combustible sealant
7 ft (2134 mm)
minimum
floor to ceiling
22 in./559 mm
minimum
12 in./305 mm
minimum