12
afreeareaofonesquare inchper1000Btu/hr(22cm2/kW)ofthe
totalinputofallappliancesintheenclosure, butnotlessthan100
squareinches(645cm2).
Iftheconnedspaceiswithinabuildingof tightconstruction,airfor
combustion and ventilation must be obtained from outdoors. When
directlycommunicatingwiththeoutdoorsorcommunicatingthrough
verticalducts,twopermanentopenings,locatedintheabovemanner,
shallbeprovided. Eachopeningshall haveafree areaofnot less
thanonesquareinchper4000Btu/hr(5.5cm2/kW)oftotalinputofall
appliancesintheenclosure.Ifhorizontalductsareused,eachopening
shallhaveafreeareaofnotlessthanonesquareinchper2000Btu/
hr(11cm2/kW)ofthetotalinputofallappliancesintheenclosure.
a. all aIr froM InsIde BuIldInGs: (SeeFigure5and6)
Theconned space shall be provided with two permanent openings
communicatingdirectly with an additional room(s) of sufcient volume
sothat the combined volume of all spaces meets the criteria for an
unconnedspace.Thetotalinputofallgasutilizationequipmentinstalled
inthecombinedspaceshallbeconsideredinmakingthisdetermination.
Eachopening shall have a minimum free area of one square inch
per1,000 Btu per hour (22 cm2/kW) of the total input rating of all gas
utilizationequipmentintheconnedspace,butnotlessthan100square
inches(645 cm2). One opening shall commence within 12 inches
(30cm)ofthetopandonecommencingwithin12inches(30cm)ofthe
bottom of the enclosures.
FIGURE 6.
B. all aIr froM outdoors:(SeeFigures7,8and9)
Theconnedspaceshallbeprovidedwithtwopermanentopenings,
onecommencing within 12 inches (30 cm) of the top and one
commencingwithin12inches(30cm)fromthebottomoftheenclosure.
Theopeningsshallcommunicatedirectly,orbyducts,withtheoutdoors
orspaces(crawlorattic)thatfreelycommunicatewiththeoutdoors.
1. W hendi rect lycom muni cati ngwit htheo utdo ors,e acho penin gsha llhav e
aminimumfreeareaof1squa reinchper4,000Btuperh our(5.5cm2/kW)
oftotalinputratingofallequipmentinthee nclosure,seeFigure7.
FIGURE 7.
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(5.5cm2/kW)oftotalinputratingofallequipmentinthe
enclosure,seeFigure8.
3. Whencommunicatingwiththeoutdoorsthroughhorizontalducts,each
openingshallhavea minimumfreeareaof 1squareinchper 2,000
Btuperhour(11cm2/kW))oftotalinputratingofallequipmentinthe
enclosure,seeFigure9.
FIGURE 8.
4. When ducts are used, they shall be of the same cross-sectional area
asthefreeareaoftheopeningstowhichtheyconnect.Theminimum
shortsidedimensionofrectangularairductsshallnotbelessthan3
inches(7.6cm),seeFigure9.
FIGURE 9.
5. Alternatively a single permanent opening may be used when
communicatingdirectlywiththeoutdoors,orwithspacesthatfreely
communicatewiththeoutdoors.Theopeningshallhaveaminimum
freeareaof1 squareinchper 3,000BTUperhour (8.3cm2/kW)of
totalinputratingofallequipmentinenclosure.SeeFigure9A.
FIGURE 9.
6.LouversandGrilles:Incalculatingfreearea,considerationshallbegiven
to
theblockingeffectoflouvers,grillesorscreensprotectingopenings.Screens
usedshallnotbesmallerthan1/4inch(6.4mm)mesh.Ifthefreeareathrough
adesignoflouveror grilleisknown,itshould beusedincalculatingthe size
openingrequiredtoprovidethefreeareaspecied.Ifthedesignandfreearea
isnotknown,itmaybeassumedthatwoodlouverswillbe20-25percentfree
areaandmetallouversandgrilleswillhave60-75percentfreearea.Louvers
andgrillesshallbexedintheopenpositionorinterlockedwiththeequipment
sothattheyareopenedautomaticallyduringequipmentoperation.
7.SpecialConditionsCreatedbyMechanicalExhaustingorFireplaces:
operationofexhaustfans,ventilationsystems,clothesdryersor
replacesmaycreateconditionsrequiringspecialattentiontoavoid
unsatisfactoryoperationofinstalledgasutilizationequipment.