INSTALLATION CONSIDERATIONS
13
9.3.2.2* Known Air Infiltration Rate Method.
Where the air infiltra
-
tion rate of a structure is known, the minimum required volume shall
be determined as follows:
(1) For appliances other than fan-assisted, calculate using the following
equation:
Required Volume
other
≥
21 ft
3
(
I
other
)
ACH
1000 Btu/hr
(2) For fan-assisted appliances, calculate using the following equation:
Required Volume
fan
≥
15 ft
3
(
I
fan
)
ACH
1000 Btu/hr
where:
I
other
=
all appliances other than fan-assisted input in Btu per hour
I
fan
=
fan-assisted appliances input in Btu per hour
ACH
=
air change per hour (percent of volume of space exchanged
per hour, expressed as a decimal)
(3) For purposes of this calculation, an infiltration rate greater than 0.60
ACH
shall not be used in the equations in 9.3.2.2(1) and 9.3.2.2(2).
9.3.2.3 Indoor Opening Size and Location.
Openings used to connect
indoor spaces shall be sized and located in accordance with the following:
(1)*
Combining spaces on the same story.
Each opening shall have a
minimum free area of 1 in.
2
/1000Btu/hr (2200 mm
2
/kW) of the total
input rating of all appliances in the space but not less than 100 in.
2
(0.60m
2
). One opening shall commence within 12 in. (300 mm) of
the top, and one opening shall commence within 12 in. (300 mm) of
the bottom, of the enclosure
[see Figure A.9.3.2.3(1)].
The minimum
dimension of air openings shall be not less than 3 in. (80 mm).
Furnace
Water
Heater
Opening
Chimney or Gas Vent
Opening
NOTE: Each opening must have
a free area of not less than one
square inch per 1000 BTU of
the total input rating of all equip-
ment in the enclosure, but not
less than 100 square inches.
Figure A.9.2.3.3.(1) All Combustion Air from Adjacent
Indoor Spaces through Indoor Combustion Air Openings.
(2)
Combining spaces in different stories
.
The volumes of spaces in
different stories shall be considered as communicating spaces where
such spaces are connected by one or more openings in doors or floors
having a total minimum free area of 2 in.
2
/1000 Btu/hr (4400 mm
2
/
kW) of total input rating of all appliances.
9.3.3 Outdoor Combustion Air.
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 dimension of air openings
shall not be less than 3 in. (80 mm).
9.3.3.1 Two Permanent Openings Method.
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 communicate 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 commu-
nicating 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
NOTE: The inlet and outlet air
openings must each have a free
area of not less than one square
inch per 4000 BTU of the
total input rating of all equipment
in the enclosure.
Inlet Air
Ventilation louvers for
unheated crawl space
Alternate
air inlet
Ventilation louvers
(each end of attic)
Figure A.9.3.3.1(1)(a) All Combustion Air From Outdoors -
Inlet Air from Ventilated Crawl Space and Outlet Air
to Ventilated Attic.
Furnace
Water
Heater
Outlet Air
Chimney or Gas Vent
NOTE: The inlet and outlet air
openings must each have a free
area of not less than one square
inch per 4000 BTU of the
total input rating of all equipment
in the enclosure.
Inlet air duct
[ends 1 ft (300 mm)
above floor]
Ventilation louvers
(each end of attic)
Figure A.9.3.3.1(1)(b) All Combustion Air
From Outdoors through Ventilated Attic.
(2)* Where communicating with the outdoors through horizontal 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).]
Required Volume
other
≥
21 ft
3
(
I
other
)
ACH
1000 Btu/hr