C. ACCESSIBILITY CLEARANCES
1. The PUREFIRE
®
boiler is certified for closet installations
with zero clearance to combustible construction. In
addition, it is design certified for use on combustible
floors. Do not install on carpeting.
2. Figure 1.1 shows the minimum recommended
clearances to allow reasonable access to the boiler for
inspection and maintenance. However, local codes or
special conditions may require greater clearances.
D. COMBUSTION AND VENTILATION AIR
1. The PUREFIRE
®
boiler is designed for operation with
combustion air piped directly to the boiler from
outside the building (sealed combustion). Combustion
air can be supplied from within the building only if
adequate combustion and ventilation air is provided
in accordance with the section of the National Fuel
Gas Code entitled, “Air for Combustion and
Ventilation” or applicable provisions of the local
building codes.
2. If the combustion air is piped directly to the boiler
from outside the building, no additional combustion
or ventilation air is required. Otherwise, follow the
National Fuel Gas Code recommendations
summarized in subsections 3 through 10.
3. 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, 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.
3
PREINSTALLATION
Figure 1.1: Minimum Accessibility Clearances – PF-850, PF-1000
15 ft
3
I
fan
ACH 1000
Btu
/
hr
Required Volume
fan
=
⎛
⎜
⎝
⎛
⎜
⎝
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