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3
PREINSTALLATION
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 m
3
/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, PB Heat recommends 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 appliances other than fan assisted and
for the Series 211A Boiler shall be determined
as follows:
where:
I
other
= Input of appliances other than fan
assisted in Btu/hr
ACH = air change per hour (percent of the
volume of the space exchanged per
hour, expressed as a decimal)
For fan assisted appliances, calculate the required
volume of air using the following equation:
I
fan
= Input of the fan assisted appliances 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
1.2 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 1.3 for an
illustration of this arrangement.
4. Outdoor Combustion Air:
Outdoor combustion air is
to be provided through one or two permanent
openings. The minimum dimension of these air
openings is 3 inches (76 mm).
a. Two Permanent Opening Method: Provide
two permanent openings. One opening is to
begin within 12 inches (305 mm) of the top of
the space and the other is to begin within 12
inches (305 mm) of the floor. The openings are
to communicate directly or by ducts with the
outdoors or with spaces that freely communicate
with the outdoors. The size of the openings shall
be determined as follows:
21 ft
3
I
other
ACH 1000
Btu
/
hr
Required Volume
other
=
⎛
⎜
⎝
⎛
⎜
⎝
Figure 1.2: Air Openings – All Air from Indoors
on the Same Floor
Figure 1.3: Air Openings – All Air from Indoors
on Different Floors
15 ft
3
I
fan
ACH 1000
Btu
/
hr
Required Volume
fan
=
⎛
⎜
⎝
⎛
⎜
⎝