Combustion Air and Ventilation
for Appliances Located in
Unconfined Spaces
Unco_,fined Space is a space whose volume is not Jessthan 50
cubic feet per 1,000 Btu per hour of theaggregate input rating
of all appliances installed in thatspace_Roomscommunicating
directly with the space in which the appliances are installed,
through openings not furnished with doors, are considered a
part of theunconfined space
In unconfined spacesin buildings, infiltration may be adequate
to provide air for combustion, ventilation and dilution of flue
gases,However, in buildings of tight construction (for example,
weather stripping, heavily insulated, cau]ked, vapor barrier,
etc.) additional air may needto beprovided using the methods
described in Combustion Air and Ventilation for App lances
Locatedin Confined Spaces,b
Combustion Air and Ventilation
for Appl nces Located in
Confined Spaces
Confined Space is a space whose volume is lessthan 50 cubic
feet,per 1,000 Btuper hour of the aggregateinput rating of all
appliancesinstalledin that space,
a.ALLAIR FROM INSIDE BUILDINGS:
(SeePageg Figure 1,and Figure 2 below)
The confined space shall be provided with two permanent
openingscommunicating directly with an additional room(s)
of sufficient volume so that the combined volume of all
spacesmeetsthe criteria for an unconfined space The total
inputof all gas utilization equipment installed in the com-
bined space shall be considered in making this determina-
tion. Each opening shall have a minimum free area of one
squareinch per 1,000 8TU per hour of the total input rating
of a!l gas utilization equipment in the confined space, but
not less than I00 square inches. One opening shall com-
mence within 12 inches of the top and one commencing
within 12 inchesof the bottom of the enclosure
i---7FUN OPEN{_IGS
b. ALLAIR FROMOUTDOORS: (see Figures 3-51
The confined space shall be provided with two perma-
nent openings, one commencing within 12 inches of the
top and one commencing within 12 inches from the bot-
tom of the enclosure. The openings shall communicate
directly, or byducts, with the outdoorsor spaces(crawl or
attic) that freely communicate with the outdoors..
Figure 3i
ALT IIILET _R VEh'_qL&T_O,b_ I*OUV'_q5
]. When directly communicating with the outdoors, each
opening shah have a minimum free area of t square inch
per 4,000 BTU per hour of total input rating of all equip-
ment in the enclosure tSee Figure 3.)
2. When communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area of 1
square inch per 4,000 BTU per hour of total input rating
of all equipment in the enclosure (SeeFigure 43
Figure4 tTER
t!,.l
3. When communicating with the outdoors through horizon-
tal ducts, each opening shall have a minimum freearea of
I square inch per 2,000 13TUper hour of total input rating
of all equipment in the enclosure (See Figure5.)
IFigure5 J
!1!" -tP
4, When ducts areused, they shall be of the samecross-sec-
tional area as the free area of the openings to _vhich they
connect. Theminimum short side dimension of rectangular
air ducts shall not be less than 3 inches (SeeFigure 5.)
5,.Louvers and Grilles: In calculating free area, consideration
shall begiven to the blocking effect of louvers, grilles or
screens protecting openings. Screens used shall not be
smaller than % inch mesh If the free area through a design
of louver or grille is known, it should be used in calculat-
ingthe size opening required to provide the freearea spec-
ified,. If the-design and free area is not known, it may be
assumedthat wood louverswill be 20-25 percent free area
and meta] louvers and grilles will have 60-75 percent free
area.Louvers and grillesshall be fixed in the open position
or interlocked with the equipment so that they are opened
automatically during equipment operation.
6 Special Conditions Created by Mechanical Exhausting or
Fireplaces:Operation of exhaust fans,ventilation systems,
clothes dryersor fireplaces may create conditions requiring
special attention to avoid unsatisfactory operation of
installedgas utilization equipment.