Weil-McLain SVF 1500 Manual page 38

SVF
™
Series 1
Commercial Condensing Gas-Fired Water Boiler — Boiler Manual
DIRECT VENT — Boiler room air openings
Combustion/ventilation air provision
For direct vent installations, combustion air must be ducted
directly from outside to the boiler air intake fi tt ing. Two options
are available: sidewall or vertical direct vent. Th ough combus-
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tion air is ducted to the SVF
require air openings, either for ventilation or for combustion
air for other appliances plus ventilation.
Sizing air openings
Air openings provide for ventilation (as well as combustion air)
to prevent overheating of the boiler controls and boiler space.
Air is also needed for other appliances located in the same space.
Use Figure 33, page 39, selecting the appropriate installation
conditions.
Air openings must be sized to handle all appli-
ances and air movers (exhaust fans, etc.) using
the air supply.
Th e sizing given in Figure 33, page 39 is based on the National
Fuel Gas Code - ANSI Z223.1/NFPA 54 – latest edition, al-
lowing adequate air opening for gravity-vented gas appliances
(Category I) when located in the same space as the SVF
When outside air is ducted as directed in this manual, the SVF
boiler is rated as direct vent (pressurized vent), and has varying
requirements for combustion and ventilation air, refl ected by the
special sizing instructions given in Figure 33, page 39.
Th e air openings recommended in Figure 33, page 39 will allow
adequate ventilation and combustion air provided the boiler
room is not subjected to negative pressure due to exhaust fans
or other mechanical ventilation devices. Refer to the National
Fuel Gas Code for dealing with other conditions.
Louver allowance
Th e free area of openings means the area
any installed louvers or grilles
reduction when sizing the air openings.
Special considerations
Tight construction
ANSI Z223.1/NFPA 54 defi nes unusually tight construction
where:
1. Walls and ceilings exposed to the outside atmosphere have
a continuous water vapor retarder with a rating of 1 perm
or less with openings gasketed, and . . .
2. Weather-stripping has been added on openable windows
and doors, and . . .
3. Caulking or sealants are applied to areas such as joints
around windows and door frames, between sole plates and
fl oors, between wall-ceiling joints, between wall panels, at
penetrations for plumbing, electrical, and gas lines, and in
other openings.
For buildings with such construction, provide air openings
into the building from outside, sized per the appropriate case
in Figure 33, page 39 if appliances are to use inside air for com-
bustion and ventilation.
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boiler, the boiler room will still
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boiler.
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after reduction for
. Be sure to consider this
Exhaust fans and air movers
Th e appliance space must never be under a negative pressure unless all ap-
pliances are installed as direct vent. Always provide air openings sized not
only to the dimensions required for the fi ring rate of all appliances, but also
to handle the air movement rate of the exhaust fans or air movers using air
from the building or space.
Manifolded combustion air option
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1. Multiple SVF
boilers can use a common combustion air manifold.
a. Size the duct to provide at least 1 square inch per 2,000 Btuh total
input of connected boilers.
b. Provide minimum clearance to adjacent vents and grade/snow line
as shown in Figure 32 .
c. Provide minimum free area in duct (adjusted for louver restriction)
1 square inch per 2,000 Btuh
of
the total MBH (1000's Btuh) by 2.
d. Example: For an MBS system with total input of 3,000,000 Btuh,
or 3,000 MBH: Divide 3,000 by 2 = 1500 square inches minimum
for a combined air duct.
and boiler component damage can occur. Failure to
or substantial property damage.
Figure 32
Manifolded combustion air option
total boiler input, or divide
Part number 550-100-250/0819