Form I-XE/CRGB/RPB, Mfg No. 131782 Rev 4, Page 7
5. Clearances
Provide clearance to combustibles as shown in the table. Clearance to
combustibles is defined as the minimum distance from the heater to a
surface or object that is necessary to ensure that a surface temperature
of 90°F above the surrounding ambient temperature is not exceeded.
Clearance is also required to sides of furnace for combustion air space
and for convenient installation and burner control system service.
6. Combustion Air Requirements
6A. Indoor, Gravity-Vented Models XE/HXE
These furnaces are designed to take combustion air from the space in
which the furnace is installed. The air that enters into the combustion
process is vented to the outdoors. Sufficient air must enter the equip-
ment location to replace the air exhausted through the vent system.
Modern construction methods involve the greater use of insulation,
improved vapor barriers and weather-stripping, with the result that
buildings generally are much tighter structurally than they have been in
the past. The combustion air supply for gas-fired equipment can be
affected by these construction conditions because infiltration that would
have existed in the past may not be adequate. Extensive use of exhaust
fans aggravates the situation. In the past the filtration of outside air
assumed in heat loss calculations (one air change per hour) was assumed
to be sufficient. However, current construction methods may now re-
quire the introduction of outside air through wall openings or ducts.
Requirements for combustion air and ventilation air depend upon whether
the unit is located in a confined or unconfined space. An "unconfined
space" is defined as a space whose volume is not less than 50 cubic feet
per 1000 BTUH of the installed appliance. Under all conditions, enough
air must be provided to ensure there will not be a negative pressure
condition within the equipment room or space. A positive seal must be
made in all return-air connections and ducts. Even a slight leak can create
a negative pressure condition in a confined space and affect combustion.
WARNING: These gravity-vented, indoor furnaces
are designed to take combustion air from the space
in which the furnace is installed and are not designed
for connection to outside combustion air intake
ducts. Use of outside air ducts voids the warranty
and could cause hazardous operation. See Hazard
Levels, page 2.
Indoor, Gravity-Vented Furnace Located in a
Confined Space
Do not
install a unit in a confined space without providing wall open-
ings leading to and from the space. Provide openings near the floor and
ceiling for ventilation and air for combustion as shown in
FIGURE 2
,
depending on the combustion air source as noted in Items 1, 2 and 3.
Add total BTUH of all appliances in the confined space and divide by
figures below for square inch free area size of each (top and bottom)
opening.
1. Air from inside the building
- openings 1 square inch free area per
1000 BTUH. Never less than 100 square inches free area for each open-
ing. See (1) in
FIGURE 2
.
2. Air from outside through duct
- openings 1 square inch free area per
2000 BTUH. See (2) in
FIGURE 2
.
3. Air direct from outside
- openings 1 square inch free area per 4000
BTUH. See (3) in
FIGURE 2
.
NOTE:
For further details on supplying combustion air to confined
space, see National Fuel Gas Code ANSI Z223.1a (latest edition) 5.3.3.
6B. Combustion Air for Gravity-Vented,
Outdoor Model Series CRGB
Combustion air enters through the screened air intakes located in the
furnace section access doors.
6C. Combustion Air for Power-Vented,
Outdoor Model
Series RPB
The combustion air and flue gas
openings are carefully designed
screened openings located on the
side of the unit just above the con-
trol access panel. Location of the
flue opening directly above the air
intake is designed to discourage re-
circulation of combustion prod-
ucts. See
FIGURE 3.
6D. Chlorine - All Models
The presence of chlorine vapors in the combustion air of gas-fired heat-
ing equipment presents a potential corrosion hazard. Chlorine will,
when exposed to flame, precipitate from the compound, usually freon
or degreaser vapors, and go into solution with any condensation that is
present in the heat exchanger or associated parts. The result is hydro-
chloric acid which readily attacks all metals including 300 grade stainless
steel.
Care should be taken to separate these vapors from the combustion
process. This may be done by wise location of the furnace with regard
to exhausters or prevailing wind direction. Remember, chlorine is heavier
than air. This fact should be kept in mind when determining installation
locations of heating equipment and building exhaust systems.
7. Suspending/Mounting
7A. Suspending/Mounting Indoor, Gravity-
Vented Models XE/HXE
Location
- Before suspending the furnace, check the supporting struc-
ture to verify that it has sufficient load-carrying capacity to support the
weight of the unit.
Approximate Net Weight - Indoor Furnaces
S i z e
75-100
125
150-175
200-225
250-300 350
400
lbs
233
295
332
386
494
515
576
kg
106
134
151
175
224
234
261
WARNING: Avoid installing a unit in an extremely
drafty area. Extreme drafts can shorten the life of
the heat exchanger and/or cause safety problems.
FIGURE 2 -
Confined Space: A
space whose volume
is less than 50
cubic feet per 1000
BTUH of the
installed appliance
input rating
Confined
Space
(1)
(1)
(2)
(2)
(3)
(3)
Flue Products
Outlet
Combustion
Air Inlet
FIGURE 3 - Combustion Air
Intake, Power-Vented
Models
REQUIRED CLEARANCES
Sides
Bottom
Model S eries
Top
Control
Opp osite
To
Combustibles
To Non-
Combustibles
(H)XE
6"
(152mm)
6"
(152mm)
3" (76mm)
0
(H)RPB,
(H)CRGB
36"
(915mm)
6"
(152mm)
0 *
0
(H)CRGB
30' (9M) radius from center of vent cap to obstructions
such as walls, parapets or cupolas
Width of
furnace
p lus 6"
(152mm)
* When installed on a roof curb on a combustible roof, the roof area enclosed
within the curb must be either ventilated, left op en, or covered with non-
combustible material which has an "R" value at least 5.0. See
FIGURE 8
, page 10.
