13
1.
Determine volume of space (boiler room). Rooms
communicating directly with the space in which
appliances are installed, through openings not furnished
with doors, are considered a part of the space.
Volume (ft
3
) = Length (ft.) x Width (ft.) x Height (ft.)
2.
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/hr.
3.
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/hr, then it is considered
an
unconfined space
. If the result is less than 50
ft
3
/1000 BTU/hr, then the space is considered a
confined space.
4.
When a boiler is located in an unconfined space of a
conventionally constructed building, fresh air infiltration
through cracks around windows and doors normally
provides adequate air for combustion and ventilation.
5.
Provide outdoor air for boiler located in a confined
space or an unconfined space in a building of unusually
tight construction. Outdoor air may be provided with
the use of two permanent openings which communicate
directly or by duct with the outdoors or spaces
(ventilated crawl or attic) freely communicating with
the outdoors. Locate one opening within 12 inches
of top of space. Locate remaining opening within 12
inches of bottom of space. Size each opening per the
following:
A. Direct communication with outdoors:
Minimum free area of 1 square inch per 4,000 BTU
per hour input of all equipment in space.
B. Vertical Ducts:
Minimum free area of 1 square
inch per 4,000 BTU per hour input of all equipment
in space. Duct cross-sectional area shall be same
as opening free area.
C. Horizontal Ducts
: Minimum free area of 1 square
inch per 2,000 BTU per hour input of all equipment
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 the 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.
6.
Louvers and Grilles of Ventilation Ducts
A. 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.
B.
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% free area and metal louvers and grilles
have 60-75% free area.
C.
Louvers and grilles must be fixed in the open
position, or interlocked with the equipment to open
automatically during equipment operation.
Figure 3 - Air Openings For Boiler Located In
Confined Space (Utility Room)
WARNING
Asphyxiation, fire hazard. Do not obstruct air
openings to combustion area. Follow instructions
below, to maintain adequate combustion air.
!
NOTICE
Install outside air intake if used with a fireplace or
kitchen or bathroom exhaust fan. These devices rob
boiler and water heater of combustion air.
7 - FRESH AIR FOR COMBUSTION
PN 240013415 REV A [08/15/2021]
