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e. For boiler located in a building of other than
unusually tight construction, adequate
combustion and ventilation air is normally
provided by fresh air inltration through
cracks around windows and doors.
f. For boiler located
in building of unusually
tight construction, provide outdoor air
through two permanent openings which
communicate directly or by duct with the
outdoors or spaces (crawl or attic) freely
communicating with the outdoors. Locate
one opening within 12 inches (30.5cm) of
top of space. Locate remaining opening
within 12 inches (30.5cm) of bottom of
space. Minimum dimension of air opening is
3 inches (7.6cm). Size each opening per
following:
i. Direct communication with outdoors.
Minimum free area of 1 square inch
(6.5cm
2
) per 4,000 Btu per hour input of
all equipment in space.
ii. Vertical ducts. Minimum free area of 1
square inch (6.5cm
2
) per 4,000 Btu per
hour input of all equipment in space. Duct
cross-sectional area shall be same as
opening free area.
iii. Horizontal ducts. Minimum free area of 1
square inch (6.5cm
2
) per 2,000 Btu per
hour input of all equipment in space. Duct
cross-sectional area shall be same as
opening free area.
g. Ventilation Duct Louvers and Grilles. Equip
outside openings with louvers to prevent
entrance of rain and snow, and screens to
prevent entrance of insects and rodents.
Louvers and grilles must be xed in open
position or interlocked with equipment to
open automatically before burner operation.
Screens must not be smaller than ¼ inch
mesh.
Consider the blocking effect of louvers,
grilles and screens when calculating the
opening size to provide the required free
area. If free area of louver or grille is not
known, assume wood louvers have 20-25
percent free area and metal louvers and
grilles have 60-75 percent free area.
8. CONNECT GAS SERVICE from Meter to gas control
assembly in accordance with Local Piping Codes and
requirements of Gas Company, see Figure 1. They may
require piping of larger size than Control Assembly
Connection, especially if run from meter is long or
includes several elbows. (See Figure 1 for size of Gas
Connection to gas control assembly).
Volume [ft³](m
3
) = Length [ft](m) x Width
[ft](m) x Height [ft](m)
b. Determine Total Input of all appliances in
space. Round result to nearest 1,000 Btu per
hour (Btuh).
c. Determine type of space. Divide Volume by
Total Input.
i. If result is greater than or equal to 50 ft³
(1.4m3) per 1,000 Btuh, space is
considered an unconned space.
ii. If result is less than 50 ft³ (1.4m3) per
1,000 Btuh, space is considered a conned
space.
d. Determine building type. A building of
unusually tight construction has the
following characteristics:
i. Walls and ceiling exposed to outside
atmosphere have a continuous water vapor
retarder with a rating of 1 perm or less
with openings gasketed and sealed, and
ii. Weather-stripping has been added on
openable windows and doors, and
iii. Caulking or sealants applied in joints
around window and door frames, between
sole plates and oors, between wall-
ceiling joints, between wall panels, at
plumbing and electrical penetrations, and
at other openings.
Figure 2: Minimum Clearances