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C. PROVIDE AIR SUPPLY AND VENTILATION to
accommodate proper combustion. If natural ventila-
tion is inadequate, provide a screened opening or duct
from the boiler room to the outside. The opening or
duct must be sized so the boiler input will not exceed
4,000 BTUH/Sq. In. of free area. If other air consum-
ing appliances are near the boiler, the air inlet should
be larger. Consult respective manufacturers.
D. VENTILATION AIR must be provided to maintain
the ambient temperature at safe limits. Local and
national codes may apply and should be referenced.
1. In unconfined spaces (basement) in buildings of
conventional frame, brick, or stone construction,
infiltration normally is adequate to provide air for
ventilation.
2. In confined spaces, two permanent openings, one
near the top of the enclosure and one near the
bottom, shall be provided. Each opening shall have
a free area of not less than 1 sq. inch per 1000
BTUH of the total input of all appliances in the
space.
3. PROVIDE COMBUSTION AND VENTILATION
AIR. Local code provisions may apply and should be
referenced.
A. Determine volume of space (boiler room). Rooms
communicating directly with the space in which the
appliances are installed, through openings not fur-
nished with doors, are considered a part of the space.
Volume(ft
3
) = Length(ft) x Width(ft) x Height(ft)
B. Determine total input of all appliances in the space.
Add inputs of all appliances in the space and round the
result to the nearest 1000 BTU per hour.
C. Determine type of space. Divide Volume by total input
of all appliances in space. If the result is greater than
or equal to 50 ft
3
/1000 BTU per hour, then it is
considered an unconfined space. If the result is less
than 50 ft
3
/1000 BTU per hour then the space is
considered a confined space.
D. For boiler located in an unconfined space of a conven-
tionally constructed building, the fresh air infiltration
through cracks around windows and doors normally
provides adequate air for combustion and ventilation.
E. For boiler located in a confined space or an unconfined
space in a building of unusually tight construction,
provide outdoor air with the use of two permanent
openings which communicate directly or by duct with
the outdoors or spaces (crawl or attic) freely communi-
cating with the outdoors. Locate one opening within 12
inches of top of space. Locate remaining opening
within 12 inches of bottom of space. Minimum
dimension of air opening is 3 inches. Size each
opening per following:
1. Direct communication with outdoors. Minimum
free area of 1 square inch per 4,000 BTU per hour
input of all equipment in space.
2. Vertical ducts. Minimum free area of 1 square
inch per 4,000 BTU per hour input of all equip-
ment in space. Duct cross-sectional area shall be
same as opening free area.
3. Horizontal ducts. Minimum free area of 1 square
inch per 2,000 BTU per hour input of all equip-
ment in space. Duct cross-sectional area shall be
same as opening free area.
Alternate method for boiler located within confined
space. Use indoor air if two permanent openings
communicate directly with additional space(s) of
sufficient volume such that combined volume of all
spaces meet criteria for unconfined space. Size each
opening for minimum free area of 1 square inch per
1,000 BTU per hour input of all equipment in spaces,
but not less than 100 square inches.
F. Louvers and Grilles of Ventilation Ducts
1. All outside openings should be screened and
louvered. Screens used should not be smaller than
1/4 inch mesh. Louvers will prevent the entrance of
rain and snow.
2. Free area requirements need to consider the
blocking effect of louvers, grilles, or screens
protecting the openings. If the free area of the
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.
3. Louvers and grilles must be fixed in the open
position, or interlocked with the equipment to open
automatically during equipment operation.