ConfinedSpace
A confinedspaceis anarea witha volumelessthan50 cubic
feet (1.42 m3) par 1,000 Bto (.29 kW) par hourofthe com-
bined input ratingofall appliancesinstalled inthat space.This
definition includesfurnace closets or small equipment rooms.
When thefumace isinstalledso that supplyducts carryair cir-
culated by the furnace to areas outside the space containing
the fumace,the retumair must be handledby ducts whichare
sealedto the fumaca casing and which terminate outs;dethe
space containing the furnace. This is especially important
whenthefurnaceismountedona platformina confinedspaoe
suchas a closetor smallequipmentroom.Evena smallleak
aroundthe baseof theunitat the platformorat thereturnair
ductconnection can cause a potentiallydangerousnegaUve
pressurecondition.Airfor combusiton and ventilationcanbe
brought intothe confinedspace eitherfrominsidethe building
orfromoutside.
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM INSIDE
CHIMNEY
G24M
FURNACE
i i I I II II Ii i i i i i i
NOTE-Each opening shall have a free area of at least one square
inch (645 mmz)per 1,000 Btu (.29 kW) per hour ofthe total inputrat-
ing of all equipment in the enclosure, but not teas then 1O0square
inches (64516 mrn2).
FIGURE 1
Air from Inside
If theconfinedspacethathouses the furnace adjoinsa space
categorizedas unconfined,aircan bebroughtinby providing
two permanent openings between the two spaces. Each
opening must have a minimum free area of 1 square inch
(645 mm2) per 1,000 Btu (.29kW) per hour of total input rat-
ing of all gas-fired equipment in the confined space. Each
opening must be at least 100 square inches (64516 ram2).
One opening shallbe within 12 inches(305 mm)of thetopof
the enclosureandone opening within 12 inches (305 ram) of
the bottom. See figure 1.
Air from Outside
If airfrom outsideis broughtinfor cornbustionand ventilation,
the confinedspacemusthave two permanentopenings.One
opening shall be within 12 inches (305 mm) ofthe top of the
enclosure and one openingwithin 12 inches (305 mm) of the
bottom. These openings must communicate directly or by
ducts with the outdoorsor spaces (crawl or attic) that freely
communicate withthe outdoors or indirectlythroughvertical
ducts. Each opening shall have a minimum free area of 1
square inch(645 mm2) par 4,000 Btu (1.17 kW) per hour of
totalinput ratingof allequipmentin the enclosure.See figures
2 and 3. Whencommunicatingwith the outdoorsthroughhod-
zontal ducts, each opening shall have a minimum free area
of 1 square inch(645 mm2)par 2,000 Btu (.55 kW) par total
input ratingof all equipment in the enclosure. See figure 4.
When ducts are used, they shall be of the same cross-sec-
tionalarea as thefreearea ofthe openings towhich they con-
nect. The minimum dimension of rectangular air ducts shall
be no less than 3 inches (75 mm). In calculating free area,
the blocking effect of louvers, gdlles, or screens must be
considered. Ifthe design and free area of protective covering
is not known for calculatingthe size opening required,it may
be assumed that woodlouvers willhave 20 to 25 percentfree
area and metal louvers and grineswill have 60 to 75 percent
free area. Louvers and grillesmust be fixed in the open posi-
tionorinterlockedw_ theequipmentso thattheyare opened
automaticallydudngequipmentoperation.
Page 6
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