Raised Hearth Extension
A hearth extension may be used, but is not required for
these fireboxes.
A combustible hearth extension can be constructed flush
with, but not above the firebox floor. On flush installa
-
tions, carpet or vinyl is not allowed within 14 inches of
the firebox opening. See Figure 3.5.
Figure 3.5 Raised Hearth Extension
Firebox framing can be built before or after the appliance is
set in place. Construct firebox framing following Figure 3.3
for your specific installation requirements. Refer to Figure
3.1 on page 6 for firebox dimensions.
The firebox may be installed directly on a combustible
floor or raised on a platform. When the firebox is installed
directly on carpeting, tile, or other combustible material,
other than wood flooring, the firebox shall be installed on a
metal or wood panel extending the full width and depth of
the enclosure.
WARNING! Risk of Fire!
DO NOT fill spaces around fire
-
box with insulation or other materials. This could cause a
fire.
WARNING! Risk of Fire!
The firebox must be installed
giving full consideration to the clearance and height re-
quirements identified in this manual.
E. Constructing the Appliance Chase
A chase is a vertical box-like structure built to enclose the
firebox.
NOTICE:
These instructions are not substitutes for the
requirements of local building codes. Therefore, you MUST
check local building codes to determine the requirements
to these steps.
Chases should be constructed in the manner of all outside
walls of the home to prevent cold air drafting problems. The
chase should not break the outside building envelope in
any manner.
Walls, ceiling, base plate and cantilever floor of the chase
should be insulated. Vapor and air infiltration barriers should
be installed in the chase as per regional codes for the rest
of the home. Additionally, in regions where cold air infiltra
-
tion may be an issue, the inside surfaces may be sheet
rocked and taped (or an equivalent method may be used)
to achieve maximum air tightness.
To further prevent drafts, gas line holes and other open
-
ings should be caulked with caulk with a minimum of 300ºF
continuous exposure rating or stuffed with unfaced insulation.
If the firebox is being installed on a cement surface, a layer of
plywood may be placed underneath to prevent conducting cold
up into the room.
NOTICE:
Install firebox on hard metal or wood surfaces
extending full width and depth.
DO NOT
install directly on
carpeting, vinyl, tile or any combustible material other than
wood.
WARNING! Risk of Fire!
Maintain specified air space
clearances to firebox:
• Insulation and other materials must be secured to prevent
accidental contact.
• The chase must be properly blocked to prevent blown
insulation or other combustibles from entering and making
contact with firebox.
• Failure to maintain airspace may cause overheating and
a fire.
0" Minimum
Combustible Platform
Raised Hearth Extension
(Combustibles allowed;
No carpet or vinyl within
14 inches)
Firebox Floor
10
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21
