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.
Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
GasVent
This installation NOT approved in Canada GasVen_
GableVent j_ _i_r "_
_ alternat"_eInlet Air 11) A/ GableVent _ _ I'r-"li "''" "" "" "" "" ' " " " "" _)_",,,
' _ Ga Ven _ -- J II II rl II Outlet
I-" _ _ f'VentilatedAttic_ n.tlp_4 II _ _ Air(21
OutletAir(1) SoffitVent f ....... "_" Ai_';1; I II 3| II II
lOp ADOVe insulation _ _ / I rum, J.t I I I I
% ............... II It1 II II
2d= _ m I I _1TM J I I I I II II
• SoffitVent Inlet Inlet
I--I / 0utletA,r_,_ I1 I ,ir , ,..,tL
M / % II I
r_l , _ I I -- ,-_ II I MinimumOnelnletandOneOutletAirSupplyisRequired
', I I I I H I May bein any CombinationShown
_ _ ,.,^, / I ...... I,_1 I I I Inlet Air Openingmustbewithin 12" (304.8mm)offloor
VentilatedCrawl_ '_'.'=' _1-..I I._Z.%J _ Inl t
A,r(1) _ 1"_°7 _ _ All(2) Outlet Air Openingmustbe within 12" (304.8mm)ofceiling
(1) 1SquareInch per4000 BTUH
(2) 1SquareInch per2000 BTUH
alternateInletAir (1)
c. Horizontal duct openings require 1 square inch of free
area per 2,000 BTUH (11 cm2/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 cm2/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 cm2/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
Free Area
BTUH(kW)
Input
Rating
40,000 (11.72)
50,000 (14.65)
60,000 (17.58)
75,000 (21.98)
80,000 (23.45)
100,000 (29.31)
125,000 (36.63)
TwoHorizontalDucts
BTUH(kW)
sq.in./2,000(1cm2/.09)
20sq. in.(129cmz)
25sq. in.(161cmz)
30 sq.in. (194cmz)
37.5sq.in. (242cmz)
40sq. in.(258cmz)
50sq. in.(322cmz)
62.50sq.in. (403cmz)
EXAMPLE: Determining Free Area
Furnace Water Heater
100,000 + 30,000
29.31 8.8
Furnace Water Heater
100,000 + 30,000
29.31 8.8
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
b.
c.
Indoor
Combustion Air Method below and
Outdoor openings located as required in the Outdoor
Combustion Air Method above and
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 I 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.
MinimumFreeArea Requiredfor EachOpeningor Ductto Outdoors
SingleOpening
BTUH(kW)
sq.in./3,000(1cm2/.135)
13.34sq.in.(86cmz)
16.7sq.in. (108cmz)
20 sq. in.(129cmz)
25 sq. in.(161cmz)
26.7sq.in. (172cmz)
33.3sq.in. (215cmz)
41.7sq.in. (269cmz)
TwoVerticalDuctsor Openings
BTUH(kW)
sq.in./4,000(1cm2/.18)
10 sq.in. (65cmz)
12.5sq.in. (81cmz)
15 sq.in. (97cmz)
18.75sq. in.(121cmz)
20 sq. in,(129cmz)
25 sq. in,(161cmz)
31.25sq.in. (202cmz)
RoundDuct
BTUH(kW)
sq.in./4,000(6.5cm2/.18)
4" (101.6mm)
4" (101.6mm)
4" (101.6mm)
5" (127mm)
5" (127mm)
6" (152.4mm)
7" (177.8mm)
Total Input
(130,000 + 4,000)
(38.11+ .18)
Total Input
(130,000 + 2,000)
(38.11 + .09)
= 32.5 S_ In. Vertical
= 210 cm_Vertical
= 65 Sq. In. Horizontal
= 423 cm2 Horizontal
440 01102404
Specifications are subject to change without notice
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