GM9S80 Service Manual

SYSTEM OPERATION
14
(2) Combining spaces in dierent stories. The volumes of
󰀨-
municating spaces where such spaces are connected

minimum free area of 2 in.
2
/1000 Btu/hr (4400 mm
2
/kW)
of total input rating of all appliances.
Outdoor combustion air shall
be provided through opening(s) to the outdoors in accordance
with the methods in 9.3.3.1 or 9.3.3.2. The minimum dimen-
sion of air openings shall not be less than 3 in. (80 mm).
Two permanent
openings, one commencing within 12 in. (300 mm) of the top
and one commencing within 12 in. (300 mm) of the bottom, of
the enclosure shall be provided. The openings shall commu-
nicate directly, or by ducts, with the outdoors or spaces that
freely communicate with the outdoors, as follows:
(1)*Where directly communicating with the outdoors or
where communicating to the outdoors through vertical
ducts, each opening shall have a minimum free area of
1 in.
2
/4000 Btu/hr (550 min
2
/kW) of total input rating of all
appliances in the enclosure. [See Figure A.9.3.3.1(1)(a)
and Figure A.9.3.3.1(1)(b).]
Furnace
Water
Heater
Outlet Air
Chimney or Gas Vent



the


Inlet Air
Ventilation louvers for
unheated crawl space
Alternate
air inlet
Ventilation louvers
(each end of attic)


Furnace
Water
Heater
Outlet Air
Chimney or Gas Vent




the


Inlet air duct
[ends 1 ft (300 mm)
above floor]
Ventilation louvers
(each end of attic)


(2)*Where communicating with the outdoors through horizon-
tal ducts, each opening shall have a minimum free area
of 1 in.
2
/2000 Btu/hr (1100 min
2
/kW) of total input rating of
all appliances in the enclosure. [See Figure A.9.3.3.1(2).]
Furnace
Water
Heater
Chimney or Gas Vent


less than one 

ent in the

Outlet air duct
Inlet air duct


     One perma-
nent openings, commencing within 12 in. (300 mm) of the
top of the enclosure, shall be provided. The appliance shall
have clearances of at least 1 in. (25 mm) from the sides and
back and 6 in. (150 mm) from the front of the appliance.
The opening shall directly communicate with the outdoors
or shall communicate through a vertical or horizontal duct
to the outdoors or spaces that freely communicate with the
outdoors (see Figure A.9.3.3.2) and shall have a minimum
free area of the following:
(1) 1 in.
2
/3000 Btu/hr (700 mm
2
per kW) of the total input
rating of all appliances located in the enclosure, and
(2) Not less than the sum of the areas of all vent connectors
in the space.
Furnace
Water
Heater
Opening
Chimney or Gas Vent







Alternate
Opening
Location



The use of a combination of indoor and outdoor combustion
air shall be in accordance with (1) through (3) (see example
calculation in Annex J]:
(1) Indoor Openings: Where used, openings connecting the
interior spaces shall comply with 9.3.2.3.
(2) Outdoor Opening(s) Location. Outdoor opening(s) shall
be located in accordance with 9.3.3.