441 01 2613 06
11
Specifications are subject to change without notice.
2.
Figure 8
illustrates how to provide combustion and ventilation
air when two permanent openings, one inlet and one outlet, are
used.
a. One opening
MUST
commence within 12
″
(304.8mm) of
the floor and the second opening
MUST
commence
within 12
″
(304.8mm) of the ceiling.
b. Size openings and ducts per
Table 1
.
c.
Horizontal duct openings require 1 square inch of free
area per 2,000 BTUH (11 cm
2
/kW) of combined input for
all gas appliances in the space
(
see
Table 1)
.
d. Vertical duct openings or openings directly
communicating with the outdoors require 1 square inch
of free area per 4,000 BTUH (5.5 cm
2
/kW) for combined
input of all gas appliances in the space
(
see
Table 1).
3. When one permanent outdoor opening is used, the opening
requires:
a.
1 sq. in of free area per 3,000 BTUH (7 cm
2
/kW) for
combined input of all gas appliances in the space (see
Table 1
) and
b.
Not less than the sum of the areas of all vent connectors
in the space.
Figure 8
Furnace
Furnace
Minimum One Inlet and One Outlet Air Supply is Required
May be in and Combination Shown
Inlet Air Opening Must be Within12
″
(304.8 mm) of floor
Outlet Air Opening Must be Within12
″
(304.8 mm) of ceiling
(1) 1 Square Inch per 4000 BTUH
(2) 1 Square Inch per 2000 BTUH
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Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
This installation NOT approved in Canada
Gas Vent
Gas Vent
Gas Vent
Gable Vent
Gable Vent
Outlet
Air (1)
Outlet Air (1)
Outlet Air (1)
Furnace
Outlet
Air (2)
Optional Inlet Air (1)
Ventilated Attic
Ventilated Attic
Ventilated Crawl Space
Inlet
Air (1)
Inlet
Air (1)
Inlet
Air (1)
Inlet
Air (2)
Inlet
Air (2)
Top Above Insulation
Top Above Insulation
Soffit Vent
Soffit Vent
The opening shall commence within 12
″
(304.8mm) of the top of
the enclosure. Appliances shall have clearances of at least 1
″
(25.4mm) from the sides and back and 6
″
(152.4mm) from the
front. The opening shall directly communicate with the outdoors or
shall communicate through a vertical or horizontal duct to the
outdoors or spaces (crawl or attic) that freely communicate with
the outdoors.
4. Combination of Indoor and Outdoor Air shall have:
a. Indoor openings that comply with the
Indoor
Combustion Air
Method below and
b. Outdoor openings located as required in the
Outdoor
Combustion Air
Method above and
c.
Outdoor openings sized as follows.
1) Calculate the
Ratio
of all Indoor Space volume
divided by required volume for
Indoor Combustion Air
Method. Outdoor openings sized as follows.
2) Outdoor opening size reduction
Factor
is
1
minus the
Ratio
in 1) above.
3) Minimum size of Outdoor openings shall be the size
required in
Outdoor Combustion Air
Method above
multiplied by reduction
Factor
.
Table 1
Free Area
BTUH (kW)
Input
Rating
Minimum Free Area Required for Each Opening or Duct to Outdoors
Two Horizontal Ducts
BTUH (kW)
sq. in./2,000(1 cm
2
/.09)
Single Opening
BTUH (kW)
sq. in./3,000 (1 cm
2
/.135)
Two Vertical Ducts or Openings
BTUH (kW)
sq. in./4,000(1 cm
2
/.18)
Round Duct
BTUH (kW)
sq. in./4,000(6.5cm
2
/.18)
50,000 (14.65)
25 sq. in. (161 cm
2
)
16.7 sq. in. (108 cm
2
)
12.5 sq. in. (81 cm
2
)
4
″
(101.6mm)
75,000 (21.98)
37.5 sq. in. (242 cm
2
)
25 sq. in. (161 cm
2
)
18.75 sq. in. (121 cm
2
)
5
″
(127mm)
100,000 (29.31)
50 sq. in. (322 cm
2
)
33.3 sq. in. (215 cm
2
)
25 sq. in. (161 cm
2
)
6
″
(152.4mm)
125,000 (36.63)
62.50 sq. in. (403 cm
2
)
41.7 sq. in. (269 cm
2
)
31.25 sq. in. (202 cm
2
)
7
″
(177.8mm)
150,000 (43.95)
75 sq. in. (484 cm
2
)
50 sq. in. (322 cm
2
)
37.5 sq. in. (242 cm
2
)
7
″
(177.8mm)
EXAMPLE:
Determining Free Area
Furnace
100,000
29.31
Furnace
100,000
29.31
+
+
Water Heater
30,000
8.8
Water Heater
30,000
8.8
=
=
Total Input
(130,000
÷
4,000)
(38.11
÷
.18)
Total Input
(130,000
÷
2,000)
(38.11
÷
.09)
=
32.5 Sq. In. Vertical
=
210 c
m
2
Vertical
=
65 Sq. In. Horizontal
=
423
cm
2
Horizontal
