8
441 01 5003 01
Specifications are subject to change without notice
Requirements
1. Provide the space with sufficient air for proper combustion and
ventilation of flue gases using horizontal or vertical ducts or
openings.
2.
Figure 6
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
″
(305 mm) of the
floor and the second opening
MUST
commence within 12
″
(305 mm) 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 (1,100 mm
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 (550 mm
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 (700 mm
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.
The opening shall commence within 12
″
(305 mm) of the top of the
enclosure. Appliances shall have clearances of at least 1
″
(25.4
mm) from the sides and back and 6
″
(152 mm) 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
.
Furnace
Furnace
Minimum One Inlet and One Outlet Air Supply is Required
May be in and Combination Shown
Inlet Air Opening Must be Within12
″
(305mm) of floor
Outlet Air Opening Must be Within12
″
(305mm) of ceiling
(1) 1 Square Inch (6cm
2
) per 4000 BTUH
(2) 1 Square Inch (6cm
2
) per 2000 BTUH
Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
Figure 6
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
This installation NOT approved in Canada
Table 1
Free Area
BTUH
Input
Rating
Minimum Free Area Required for Each Opening or Duct to Outdoors
Two Horizontal Ducts
(sq. in./2,000 BTUH)
Single Opening
(sq. in./3,000 BTUH)
Two Vertical Ducts or
Openings
(sq. in./4,000 BTUH)
Rd Duct
(sq. in. /4,000 BTUH)
50,000
25 sq. in.
16.7 sq. in.
12.5 sq. in.
4
″
75,000
37.5 sq. in.
25 sq. in.
18.75 sq. in.
5
″
100,000
50 sq. in.
33.3 sq. in.
25 sq. in.
6
″
125,000
62.5 sq. in.
41.7 sq. in.
31.25 sq. in.
7
″
140,000
70 sq. in.
46.7 sq. in.
35 sq. in.
7
″
EXAMPLE:
Determining Free Area
Furnace
100,000
Furnace
100,000
+
+
Water Heater
30,000
Water Heater
30,000
=
=
Total Input
(130,000
÷
4,000)
Total Input
(130,000
÷
2,000)
=
=
32.5 Sq. In. Vertical
65 Sq. In. Horizontal
