Crown Boiler BWF Series Installation Instructions Manual page 9

5. Air for Combustion and Ventilation (continued)
This section describes methods for using indoor
combustion air. Usually, when this method is not
possible, the best approach will be to use the direct
vent kit. Instructions for installing and using the direct
vent kit are included with the kit and are also available
on our web site.
The National Fuel Gas Code does describe some
other acceptable techniques for bringing outdoor
combustion air to the boiler room, but these should
rarely be needed and are not discussed here.
A. Using the Indoor Combustion Air Method
1) Total the input of all appliances in the boiler
room in thousands of BTU/hr.
2) Find the volume of the boiler room in cubic
feet:
Volume (ft ) = Length (ft) x Width (ft) x Height (ft)
3
If the boiler room adjoins another room and there
is no door present between these two rooms,
add the volumes of the rooms together. Re-
peat for any other connected rooms which do
not have doors. Do not add the volume of
two rooms separated by a door even if that
door is "always left open" .
3) Divide the volume obtained in Step 2 by the
input calculated in Step 1.
4) If the result is at least 50 ft
and neither of the conditions described in (6)
below are met, normal infiltration should pro-
vide adequate fresh air into the boiler room.
5) If the result is less than 50 ft
hr, provide two openings into the boiler room,
one near the floor and one near the ceiling.
The top edge of the upper opening must be
within 6" of the ceiling and the bottom edge
of the lower opening must be within 6" of the
floor (Figure 5.1):
• Each opening must have a free area of
1 square inch per 1000 BTU/hr input of
all gas burning appliances in the boiler
room. The minimum opening dimension
is 3 inches. Minimum opening free area is
100 square inches per opening.
109836-01 - 04/20
per 1000BTU/hr,
3
per 1000BTU/
3
• If the total volume of both the boiler room
and the room to which the openings
connect is less than 50 cubic feet per
1000 BTU/hr of total appliance input,
install a pair of identical openings into
a third room. Connect additional rooms
with openings until the total volume of all
rooms is at least 50 cubic feet per 1000
BTU/hr of input.
• The "free area" of an opening takes into
account the blocking effect of mesh,
grills, and louvers. Where screens are
used, they must be no finer than ¼" (4 x
4) mesh.
• If providing openings into adjacent rooms
is undesirable, use the Direct Vent Kit.
6) Do not use the Indoor Combustion Air Method
described above if any of the following are
true:
a. The indoor space is so tightly con-
structed that the number of air
changes per hour is known to be 0.4
or less.
b. The boiler room is depressurized
relative to the outdoors. This depres-
surization is possible if the structure is
tightly constructed and/or is equipped
with exhaust fans.
c. The building is known to be of
unusually tight construction, which
is defined here as construction having
all of the following characteristics:
• Walls exposed to the outdoor
atmosphere having a continuous
water vapor retarder with a rating of
1 perm or less with openings
gasketed or sealed.
• Openable windows and doors are
weather stripped.
• Caulking or sealants are applied
to areas, such as joints around
window and door frames, between
sole plates and floors, between
wall-ceiling joints, between wall
panels, at penetrations for
plumbing, electrical and gas lines
and at other openings.
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