Figure 3 Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
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GasVent . GableVent)
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Soft, Vent
E_
Outlet
Air (1)
Inlet
Air(1
Furnace
Gas
fatal
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Outlel
Air (2',
Inlet
Air (2
MinimumOneInlet andOne OutletAirSupplyinRequired
May be inand CombinationShown
InletAir OpeningMustbe Within12"(300mm)of floor
OutletAir OpeningMustbe Withint2"(300ram)of ceiling
(t) 1Square Inch(6cm2)per4000 BTUR
(2)1Square Inch(6cm2)per2000 BTUH
GasVent
11
Inlet t
Air(t)
._, GableVent
f VentilatedAttic_
Top Above Insulatio_h_=
I I _ I_"
OutletAir(1) II I SoffitVent
_ Inlet
Air(2)
3.
4.
5.
One opening MUST be within 12" (300mm) of the floor and
the second opening within 12" (300mm) of the ceiling.
Size openings and ducts per Table 1.
Horizontal duct openings require 1 square inch(25sq, mm)
of free area per 2,000 BTUH of combined input for all gas
appliances in area (see Table 1).
Vertical duct openings or openings directly to outside re-
I 3
qu're 1 square inch(6.5mm ) of free area per 4,000 BTUH
for combined input of all gas appliances in area (see Table
t).
(16 cm) from the front of the appliance. The opening shall directly
communicate with the outdoors or shall communicate through a
vertical orhorizontal duct to the outdoors or spaces (crawl or attic)
that freely communicate with the outdoors, and shall have a mini-
mum free area of:
• 1sq. in per 3000 Btu per hr (7cm 2 per kW) of the total input
rating of all equipment located in the enclosure, and
• Not less than the sum of the areas of all vent connectors in
the confined space.
UnconfinedSpace Installation
Table1
FreeArea
MinimumFreeArea RequiredforEach Opening
BTUHIn-
putRat- HorizontalDuct
ing (2,000BTUH)
50,000 161cm2(25 sq. in.)
75,000 242cm2(35.5sq.in.)
100,000 323 cm 2 (50 sq. in.)
125,000 403 cm 2 (62.5 sq. in.)
150,000 484 cm 2 (71 sq. in.)
VerticalDuctoropenings
to outside
(4,000BTUH)
81 cm2(12.5sq.in.)
121cm2(18.75sq. in.)
161 cm 2(25 sq. in.)
202 cm 2 (31.25 sq. in.)
242 cm2 (37.5 sq. in.) 7"
Round
Duct
(4,000
BTUH)
4"
5"
6"
7"
EXAMPLE: Determining Free Area
Furnace Water Heater Total Input
100,000 + 30,000 = (130,000 + 4,000) = 210 cm2
(32.5 Sq. In.) Vertical
Furnace Water Heater Total Input
100,000 + 30,000 = (130,000 + 2,000) = 210 cm 2
(65 Sq. In.) Horizontal
One permanent opening, commencing within 12" (30 cm) of the
top of the enclosure, shall be permitted where the equipment has
clearances of at least 1" (2.5 cm) from the sides and back and 6"
Poison carbon monoxide gas hazard.
Most homes will require additional air.
An unconfined space or homes with tight construc-
tion may not have adequate air infiltration for proper
combustion and ventilation of flue gases.
Failure to supply additional air by means of ventila-
tion grilles or ducts could result in personal injury
and/or death.
An unconfined space is defined as an area having a minimum vol-
ume of 50 cubic feet(1.4m 3)per 1,000 Btuh total input rating for all
gas appliances in area.
Adjoining rooms can be considered part of an unconfined area if
there are no doors between rooms.
An attic or crawl space may be considered an unconfined space
provided there are adequate ventilation openings directly to out-
doors. Openings MUST remain open and NOT have any means
of being closed off. Ventilation openings to outdoors MUST be at