Infiltration rates greater than 0.60 ACH shall not be used. The
minimum required volume of the space varies with the number of
ACH and shall be determined per Table 2 or Equations 1 and 2.
Determine the minimum required volume for each appliance in the
space and add the volumes together to get the total minimum
required volume for the space.
Table 2-Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1-2002/NFPA 54-2002,8.3.2.2:
1. For other than fan-assisted appliances, such as a draft
hood-equipped water heater:
2. For fan-assisted appliances such as this furnace:
If:
I
other
= combined input of all other than fan-assisted appli-
ances in Btu/hr
I
fan
= combined input of all fan-assisted appliances in Btu/hr
ACH = air changes per hour (ACH shall not exceed 0.60.)
The following requirements apply to the Standard Method and to
the Known Air Infiltration Rate Method.
1. Adjoining rooms can be considered part of a space if:
a. There are no closable doors between rooms.
b. Combining spaces on same floor level. Each opening
shall have free area of at least 1 in.
2
/1,000 Btuh (2,000
mm
2
/kW) of the total input rating of all gas appliances in
the space, but not less than 100 in.
2
(0.06 m
2
). One
opening shall commence within 12″ (300 mm) of the
ceiling and the second opening shall commence within
12″ (300 mm) of the floor. The minimum dimension of
air openings shall be at least 3 in. (80 mm). (See Fig. 19.)
c. Combining space on different floor levels. The volumes
of spaces on different floor levels shall be considered as
communicating spaces if connected by one or more
permanent openings in doors or floors having free area
of at least 2 in.
2
/1,000 Btuh (4,400 mm
2
/kW) of total
input rating of all gas appliances.
2. An attic or crawlspace may be considered a space that freely
communicates with the outdoors provided there are ad-
equate permanent ventilation openings directly to outdoors
having free area of at least 1-in.
2
/4,000 Btuh of total input
rating for all gas appliances in the space.
3. In spaces that use the Indoor Combustion Air Method,
infiltration should be adequate to provide air for combus-
tion, permanent ventilation and dilution of flue gases.
However, in buildings with unusually tight construction,
additional air MUST be provided using the methods de-
scribed in the Outdoor Combustion Air Method section.
Unusually tight construction is defined as
Construction with:
a. Walls and ceilings exposed to the outdoors have a
continuous, sealed vapor barrier. Openings are gasketed
or sealed and
b. Doors and openable windows are weatherstripped and
c. Other openings are caulked or sealed. These include
joints around window and door frames, between sole
plates and floors, between wall-ceiling joints, between
wall panels, at penetrations for plumbing, electrical and
gas lines, etc.
NOTE: In determining the free area of an opening, the blocking
effect of the louvers, grilles, and screens must be considered. If the
free area of a louver or grille design is unknown, it may be
assumed that wood louvers have a 20 percent free area, and metal
louvers or grilles have a 60 percent free area. Screens, when used,
must not be smaller than 1/4-in. mesh. Louvers and grilles must be
constructed so they cannot be closed.
When combustion air ducts are used, they must be of the same
cross sectional area as the free area of the openings to which they
connect. The minimum dimension of ducts must not be less than 3
in. (80mm).
Combination of Indoor and Outdoor Air
1. Indoor openings shall compy with the Indoor Combustion
Air Method below and,
2. Outdoor openings shall be located as required in the
Outdoor Combustion Air Method mentioned previously
and,
3. Outdoor openings shall be sized as follows:
a. Calculate the Ratio of all Indoor Space volume divided
by required volume for Indoor Combustion Air
Method below.
b. Outdoor opening size reduction Factor is 1 minus the
Ratio in a. above.
c. Minimum size of Outdoor openings shall be the size
required in Outdoor Combustion Air Method above
multiplied by reduction Factor in b. above. The mini-
mum dimension of air openings shall be not less than 3
in. (80 mm).
INSTALLATION
NOTE: The 140 size unit may NOT be installed in non-direct
vent (1-pipe) application.
I. LEVELING LEGS (IF DESIRED)
When furnace is used in upflow position with side inlet(s), leveling
legs may be desired. (See Fig. 20.) Install field-supplied,
corrosion-resistant 5/16-in. machine bolts and nuts.
NOTE: The maximum length of bolt should not exceed 1-1/2 in.
1. Position furnace on its back. Locate and drill a 5/16–in.
diameter hole in each bottom corner of furnace. (See Fig.
20.) Holes in bottom closure panel may be used as guide
locations.
2. For each hole, install nut on bolt and then install bolt and
nut in hole. (Install flat washer if desired.)
3. Install another nut on other side of furnace base. (Install flat
washer if desired.)
4. Adjust outside nut to provide desired height, and tighten
inside nut to secure arrangement.
NOTE: Bottom closure must be used when leveling legs are used.
See Bottom Closure Panel section.
A04002
Volume
Other
=
21ft
3
ACH
I
other
1000 Btu/hr
A04003
Volume
Fan
=
15ft
3
ACH
I
fan
1000 Btu/hr
—18—
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