C. AIR FOR COMBUSTION AND
VENTILATION
1. Adequate combustion air and ventilation air must be
provided in accordance with section 5.3, Air for
Combustion and Ventilation, of the
National Fuel
Gas Code
, ANSI Z223.1/NFPA 54, or Sections 7.2,
7.3 or 7.4 of CAN/CSA B149.1,
Natural Gas and
Propane Installation Code
or applicable provisions of
the local building code. Subsections 2 through 8 as
follows are based on the
National Fuel Gas Code
requirements.
2. Required Combustion Air Volume: The total required
volume of indoor air is to be the sum of the required
volumes for all appliances located within the space.
Rooms communicating directly with the space in
which the appliances are installed and through
combustion air openings sized as indicated in
Subsection 3 are considered part of the required
volume. The required volume of indoor air is to be
determined by one of two methods.
a.
Standard Method:
The minimum required
volume of indoor air (room volume) shall be 50
cubic feet per 1000 BTU/Hr (4.8 m3/kW). This
method is to be used if the air infiltration rate is
unknown or if the rate of air infiltration is known
to be greater than 0.6 air changes per hour. As
an option, this method may be used if the air
infiltration rate is known to be between 0.6 and
0.4 air changes per hour. If the air infiltration rate
is known to be below 0.4 then the
Known Air
Infiltration Rate Method
must be used. If the
building in which this appliance is to be installed
is unusually tight, we recommend that the air
infiltration rate be determined.
b.
Known Air Infiltration Rate Method:
Where
the air infiltration rate of a structure is known,
the minimum required volume of indoor air for
the Boiler and other fan assisted appliances shall
be determined as follows:
where:
I
fan
= Input of the fan assisted appliances in
Btu/hr
ACH = air change per hour (percent of the
volume of the space exchanged per
hour, expressed as a decimal)
For appliances other than fan assisted, calculate
the required volume of air using the following
equation:
I
other
= Input of appliances other than fan
assisted in Btu/hr
Note: These calculations are not to be used for
infiltration rates greater than 0.60 ACH.
3. Indoor Air Opening Size and Location: Openings
connecting indoor spaces shall be sized and located
as follows:
a.
Combining spaces on the same floor:
Provide two permanent openings communicating
with additional spaces that have a minimum free
area of 1 in
2
per 1000 Btu/hr (22 cm
2
per 1000 W)
of the total input rating of all gas fired equipment
but not less than 100 in
2
(645 cm
2
). One
opening is to begin within 12 inches (305 mm)
from the top of the space and the other is to
begin within 12 inches (305 mm) from the floor.
The minimum dimension of either of these
openings shall be 3 inches (76 mm). See Figure
1.1 for an illustration of this arrangement.
b.
Combining spaces on different floors:
Provide one or more permanent openings
communicating with additional spaces that have
a total minimum free area of 2 in
2
per 1000
Btu/hr (44 cm
2
per 1000 W) of total input rating
of all equipment. See Figure 1.2 for an
illustration of this arrangement.
PREINSTALLATION
Figure 1.1: Air Openings – All Air from Indoors
on the Same Floor
Figure 1.2: Air Openings – All Air from Indoors
on Different Floors
15 ft
3
I
fan
ACH
1000
Btu
/
hr
Required Volume
fan
=
(
)
21 ft
3
I
other
ACH
1000
Btu
/
hr
Required Volume
other
=
(
)
5
