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FIREPLACE AND HEARTH DIMENSIONS
WARNING
This appliance is for installation only in a solid-fuel
burning masonry or UL127 factory-built fireplace,
vent free appliance, or in listed ventless firebox
enclosure. It has been design certified for these
installations.
Exception: DO NOT install this appliance in a factory-
built fireplace that includes instructions stating
it has not been tested or should not be used with
unvented gas logs.
Use manufacturer's installation and clearance require-
ments as defined in their manual.
The NB and NBSC/SCR series unvented room heaters
are approved for installation into the following unvented
fireboxes: MCUF 36/42, LCUF36, GCUF, GRUF or BUF
The NB and NBSC/SCR Series unvented room heaters
may also be installed into a Ventless Firebox Enclosure for
Gas Fired Decorative Type Unvented Room Heaters per
ANSI Z21.91 (typically referred to as a "universal firebox"),
as long as firebox hearth dimensions meet the minimum
hearth dimensions shown below.
D
A
Model
NB18 w/18" Log
NB24 w/24" Log
NB24 w/30" Log
NB18SC,SCR w/18" Log
NB24SC/SCR w/24" Log
NB24SC/SCR w/30" Log
Figure 1 -
Minimum Hearth Dimensions
Monessen • NB18/24 Gas Log Set Installation/Owner's Manual • 81D0107 • Rev B • 09/16
6
C
B
A
B
C
D
26"
13"
18"
17"
29"
13"
22
⁄
"
17"
1
4
33"
13"
25
⁄
"
17"
1
4
28
⁄
"
13"
20
⁄
"
17"
1
1
2
4
31"
13"
25
⁄
"
17"
1
4
35"
13"
25
⁄
"
17"
1
4
PLACEMENT IN FIREPLACE WITH A
RESTRICTIVE BARRIER
The following are guidelines for placing a gas log set in a
fireplace that has a restrictive barrier along the bottom front
opening of the fireplace. Some examples of barriers are
glass/screen door frames and sunken/recessed fireplaces.
Height of Restriction
(x)
No Restriction
0" to 1
⁄
"
1
2
Greater than 1
⁄
" to 3"
1
2
Greater than 3"
*Any barrier greater than 3" placed in front of the gas log set is not
recommended by the manufacturer.
NOTE: Non-combustible material such as refractory brick
may be used to line the floor of the fireplace in order to
raise the height of the gas log set in relation to a restrictive
barrier. If the unit is raised, the minimum height dimension
listed in the homeowner's manual must not be exceeded.
NOTE: If the log set is equipped with a remote receiver, a
restrictive barrier may reduce the battery life by increasing
the ambient temperature inside the fireplace. Placement
of the receiver outside of the fireplace will extend the
battery life.
WARNING
Barriers such as the bottom of a glass door frame
placed in front of a gas log set can change the air
flow characteristics of the fireplace which in turn can
cause the unit to overheat and malfunction.
Height of restrictive barrier caused by glass
door frames, recessed fireplaces, etc. from
the base or bottom surface of the unit.
(Refer to table)
Glass door frames with adjustable louvers
should have the louvers fully open while
the unit is in operation
Figure 2 -
Reference Drawing of a Natural Flame Log Set in an Enclosure
FP2252
set in enclosure
NB18/NB24 Gas Log Set
Minimum Depth of
Fireplace/Firebox
13"
16"
16"
*
The log set should be placed against
or as near as possible to the rear
wall of the fireplace/firebox.
Depth of fire-
place/firebox
(Refer to table)
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