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3. PROVIDE COMBUSTION AND VENTILATION
AIR. Local code provisions may apply and should be
referenced.
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A. Determine volume of space (boiler room). Rooms
communicating directly with the space in which the
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)
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 unconned space. If the
result is less than 50 ft
3
/1000 BTU per hour then the
space is considered a conned space.
D. For boiler located in an unconned space of a
conventionally constructed building, the fresh air
inltration through cracks around windows and
doors normally provides adequate air for combus-
tion and ventilation.
E. For boiler located in a conned space or an uncon-
ned space in a building of unusually tight con-
struction, 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 communicating 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
equipment 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
equipment in space. Duct cross-sectional area
shall be same as opening free area.
Alternate method for boiler located within
conned space. Use indoor air if two perma-
nent openings communicate directly with
additional space(s) of sufcient volume such
that combined volume of all spaces meet
criteria for unconned 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.
Figure 2: Minimum Installation Clearances To
Combustible Materials
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