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, PB
Heat recommends that the air infiltration rate be
determined.
b. Known Air Infiltration Rate Method
:
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)
Note: These calculations are not to be used for
infiltration rates greater than 0.60 ACH.
4. 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 in2 per 1000 Btu/hr (22 cm2 per 1000 W) of
the total input rating of all gas fired equipment but
not less than 100 in2 (645 cm2). 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.
5. 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:
i. Where communicating directly or through
vertical ducts with the outdoors each opening
shall have a minimum free area of 1 in
2
per
4000 Btu/hr (22 cm
2
per 4000 W) of total
input rating for all equipment in the space. See
Figure 1.4 for openings directly
communicating with the outdoors or Figure
1.5 for openings connected by ducts to the
outdoors.
ii. Where communicating with the outdoors through
horizontal ducts, each opening shall have a
minimum free area of 1 in
2
per 2000 Btu/hr (22
cm
2
per 2000 W) of total rated input for all
appliances in the space. See Figure 1.6.
4
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
PREINSTALLATION
15 ft
3
I
fan
ACH 1000
Btu
/
hr
Required Volume
fan
=
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