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19Heatilator • GDST3831I • 2127-900 Rev. K • 7/12
*C
A
A
B
D
HEADER
B. Constructing the Appliance Chase
A chase is a vertical box-like structure built to enclose the
gas appliance and/or its vent system. In cooler climates
the vent should enclosed inside the chase.
NOTICE: Treatment of ceiling fi restops and wall shield
fi restops and construction of the chase may vary with the
type of building. 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 out-
side walls of the home to prevent cold air drafting prob-
lems. The chase should not break the outside building
envelope in any manner.
Walls, ceiling, base plate and cantilever fl oor of the chase
should be insulated. Vapor and air infi ltration barriers
should be installed in the chase as per regional codes for
the rest of the home. Additionally, in regions where cold
air infi ltration may be an issue, the inside surfaces may be
sheetrocked and taped for maximum air tightness.
Figure 5.2 Clearances to Combustibles GDST3831I
C. Clearances
NOTICE: Install appliance 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 specifi ed air space
clearances to appliance and vent pipe:
• 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 fi replace or chimney.
• Failure to maintain airspace may cause overheating and
a fi re.
To further prevent drafts, the wall shield and ceiling fi re-
stops should be caulked with caulk with a minimum of
300ºF continuous exposure rating to seal gaps. Gas line
holes and other openings should be caulked with caulk
with a minimum of 300ºF continuous exposure rating or
stuffed with unfaced insulation. If the appliance is being
installed on a cement slab, a layer of plywood may be placed
underneath to prevent conducting cold up into the room.
G
F
I
E
H
* Adjust framing dimensions for interior sheathing (such as sheetrock)
MINIMUM FRAMING DIMENSIONS
GDST3831I
AB *C D E F G H I
Rough
Opening
(Width)
Rough
Opening
(Height)
Rough
Opening
(Depth)
Rough
Opening
(Width)
Clearance
to Ceiling
Combustible
Floor
Combustible
Flooring
Ends of
Appliance
Sides of
Appliance
Inches
8-5/8 34-3/4 15 38-1/8 31 0 0 1/2 36
Millimeters
219 883 381 969 787 0 0 13 914
Note: The header must
be installed on end as
shown in this diagram.