Specifications

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Specifications are subject to change without notice
11
5. When sizing a grille, louver, or screen use the free area of
opening. If free area is NOT stamped or marked on grill or
louver, assume a 20% free area for wood and 60% for metal.
Screens shall have a mesh size not smaller than
1
/
4
″ (6.4mm).
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″ (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.
Minimum One Inlet and One Outlet Air Supply is Required
May be in any Combination Shown
Inlet Air Opening must be within 12″ (304.8mm) of floor
Outlet Air Opening must be within 12″ (304.8mm) of ceiling
(1) 1 Square Inch per 4000 BTUH
(2) 1 Square Inch per 2000 BTUH
Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
Figure 6
This installation NOT approved in Canada
Gas Vent
Gable Vent
Ventilated Attic
Top Above Insulation
alternate Inlet Air (1)
Ventilated Crawl Space
Outlet Air (1)
Soffit Vent
Outlet
Air (1)
Inlet
Air (1)
Outlet
Air (2)
Inlet
Air (2)
Gas Vent
Inlet
Air (2)
Soffit Vent
Gas Vent
Gable Vent
Ventilated Attic
Top Above Insulation
Inlet
Air (1)
OutletAir (1)
alternate Inlet Air (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.
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.
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)
40,000 (11.72) 20 sq. in. (129 cm
2
) 13.34 sq. in. (86 cm
2
) 10 sq. in. (65 cm
2
) 4″ (101.6mm)
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)
60,000 (17.58) 30 sq. in. (194 cm
2
) 20 sq. in. (129 cm
2
) 15 sq. in. (97 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)
80,000 (23.45) 40 sq. in. (258 cm
2
) 26.7 sq. in. (172 cm
2
) 20 sq. in. (129 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)
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 cm
2
Vertical
= 65 Sq. In. Horizontal
= 423 cm
2
Horizontal