11
)
(
)
(
When the furnace is installed as a direct vent (2-pipe sys-
tem) furnace, no special provisions for air for combustion
are required. However, if this furnace is to be installed in
the same space with other gas appliances, such as a water
heater, ensure there is an adequate supply of combustion
and ventilation air for the other appliances. Refer to the
latest edition of the National Fuel Gas Code NFPA 54/ANSI
Z223.1 or CAN/CSA B149.1-15 Installation Codes or appli-
cable provisions of the local building codes for determining
the combustion air requirements for the appliances.
Most homes will require outside air be supplied to the fur-
nace area by means of ventilation grilles or ducts connect-
ing directly to the outdoors or spaces open to the outdoors
such as attics or crawl spaces.
The following information on air for combustion and ventilation
is reproduced from the
National Fuel Gas Code NFPA 54/ANSI
Z223.1 Section 9.3.
9.3* Air for Combustion and Ventilation.
9.3.1 General.
9.3.1.1
Air for combustion, ventilation, and dilution of flue gases for appli-
ances installed in buildings shall be obtained by application of one of the
methods covered in 9.3.2 through 9.3.6. Where the requirements of 9.3.2
are not met, outdoor air shall be introduced in accordance with methods
covered in 9.3.3 through 9.3.6.
Exception No. 1: This provision shall not apply to direct vent appli-
ances.
9.3.1.2
Appliances of other than natural draft design and other than Cat-
egory 1 vented appliances shall be provided with combustion, ventilation,
and dilution air in accordance with the appliance manufacturer’s instruc-
tions.
9.3.1.3
Appliances shall be located so as not to interfere with proper circu-
lation of combustion, ventilation, and dilution air.
9.3.1.4
Where used, a draft hood or a barometric draft regulator shall be
installed in the same room or enclosure as the appliance served so as to
prevent any difference in pressure between the hood or regulator and the
combustion air supply.
9.3.1.5
Makeup air requirements for the operation of exhaust fans, kitchen
ventilation systems, clothes dryers, and fireplaces shall be considered in
determining the adequacy of a space to provide combustion air require-
ments.
9.3.2 Indoor Combustion Air.
The required volume of indoor air shall be
determined in accordance with the method in 9.3.2.1 or 9.3.2.2 except that
where the air infiltration rate is known to be less than 0.40
ACH,
the method
in 9.3.2.2 shall be used. The total required volume shall be the sum of the
required volume calculated for all appliances located within the space. Rooms
communicating directly with the space in which the appliances are installed
through openings not furnished with doors, and through combustion air open-
ings sized and located in accordance with 9.3.2.3, are considered a part of
the required volume.
9.3.2.1* Standard Method.
The minimum required volume shall be 50 ft
3
per 1,000/Btu/hour (4.8m
3
/kW).
9.3.2.2* Known Air Infiltration Rate Method.
Where the air infiltration
rate of a structure is known, the minimum required volume shall be deter-
mined as follows:
(1) For appliances other than fan-assisted, calculate using the following
equation:
21 ft
3
I
other
Required Volume
other
> ________
_________
ACH
1000 Btu/hr
(2) For fan-assisted appliances, calculate using the following equation:
15 ft
3
I
fan
Required Volume
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 mini-
mum 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).
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 dif-
ferent 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.
