A.O. Smith 197835-001 Water Heater User Manual


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afreeareaofonesquareinchper1000Btu/hr(22cm
2
/kW)ofthe
totalinputofallappliancesintheenclosure,butnotlessthan100
squareinches(645cm
2
).
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,
shouldbeprovided.Eachopeningshouldhaveafreeareaofnotless
thanonesquareinchper4000Btu/hr(5.5cm
2
/kW)oftotalinputofall
appliancesintheenclosure.Ifhorizontalductsareused,eachopening
shouldhaveafreeareaofnotlessthanonesquareinchper2000Btu/
hr(11cm
2
/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should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shouldbeconsideredinmakingthisdetermination.
Eachopeningshouldhaveaminimumfreeareaofonesquareinch
per1,000Btuperhour(22cm
2
/kW)ofthetotalinputratingofallgas
utilization
equipmentintheconnedspace,butnotlessthan100square
inches(645cm
2
).Oneopeningshould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confinedspaceshould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shouldcommunicatedirectly,orbyducts,
withtheoutdoorsorspaces(crawlorattic)thatfreelycommunicate
with the outdoors.
1. Whendirectlycommunicatingwiththeoutdoors,eachopeningshould
have
aminimumfreeareaof1squareinchper4,000Btuperhour(5.5cm
2
/
kW)
oftotalinputratingofallequipmentintheenclosure,seeFigure7.
FIGURE 7.
2.Whencommunicatingwiththeoutdoorsthroughverticalducts,each
openingshould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should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should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should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should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shouldbe
givento
theblockingeffectoflouvers,grillesorscreensprotectingopenings.
Screensusedshould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should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.
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