441 01 2314 06
Specifications are subject to change without notice.
7
1. Provide the space with sufficient air for proper combustion and
ventilation of flue gases using horizontal or vertical ducts or
openings.
2.
Figure 3
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
.
Furnace
Furnace
Minimum One Inlet and One Outlet Air Supply is Required
May be in and Combination Shown
Inlet Air Opening Must be Within 12
″
(304.8 mm) of floor
Outlet Air Opening Must be Within 12
″
(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.)
Figure 3
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
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 ap-
pliances 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 com-
bined 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.
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
″
from the front. The open-
ing shall directly communicate with the outdoors or shall communi-
cate 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
Combus-
tion 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.
2) Outdoor opening size reduction
Factor
is
1
minus the
Ratio
in 1) above.
3) Minimum size of Outdoor openings shall be the size re-
quired in
Outdoor Combustion Air
Method above multi-
plied 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
