- Instruction Manual Residential Gas Water Heater

12
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,
shallbeprovided. Eachopeningshall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
shall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 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 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 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. Whendirectlyc ommunic atingwiththeoutdoors,eachopeningshall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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.