A.O. Smith BL-100 - Unconfined Space; Confined Space; Fresh Air Openings For Confined Spaces; Outdoor Air Through Two Openings

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amountofcombustionaircanresultinareorexplosionandcauseproperty
damage,seriousbodilyinjuryordeath.
UNCONFINED SPACE
AnUnconfinedSpaceisonewhosevolumeisnotlessthan50
cubic feet per 1,000 Btu/hr (4.8 cubic meters per kW) of the
totalinputratingofallappliancesinstalledinthespace.Rooms
communicatingdirectlywiththespace,inwhichtheappliances
are installed, through openings not furnished with doors, are
consideredapartoftheunconfinedspace.
Makeupairrequirementsfortheoperationofexhaustfans,kitchen
ventilationsystems,clothes dryers and fireplacesshallalso be
considered in determining the adequacy of a space to provide
combustion,ventilationanddilutionair.
UNUSUALLY TIGHT CONSTRUCTION
Inunconfinedspacesinbuildings,infiltrationmaybeadequateto
provideairforcombustion,ventilationanddilutionoffluegases.
However,inbuildingsofunusuallytightconstruction(forexample,
weatherstripping,heavilyinsulated,caulked,vaporbarrier,etc.)
additionalairmustbeprovidedusingthemethodsdescribedin
theConfinedSpacesectionthatfollows.
CONFINED SPACE
AConnedSpaceisonewhosevolumeislessthan50cubicfeetper
1,000Btu/hr(4.8cubicmetersperkW)ofthetotalinputratingofall
appliancesinstalledinthespace.
Openingsmustbeinstalledtoprovidefreshairforcombustion,ventilation
and dilution in conned spaces. The required size for the openings is
dependentonthemethodusedtoprovidefreshairtotheconnedspace
andthetotalBtu/hrinputratingofallappliancesinstalledinthespace.
DIRECT VENT APPLIANCES
Appliances installed in a Direct Vent conguration that derive all
air for combustion from the outdoor atmosphere through sealed
intakeairpipingarenotfactoredinthetotalapplianceinputBtu/hr
calculationsusedtodeterminethesizeofopeningsprovidingfresh
airintoconnedspaces.
EXHAUST FANS
Whereexhaustfansareinstalled,additionalairshallbeprovided
toreplacetheexhaustedair.Whenanexhaustfanisinstalledin
thesamespacewithawaterheater,sufficientopeningstoprovide
freshairmustbeprovidedthataccommodatetherequirements
forallappliancesintheroomandtheexhaustfan.Undersized
openingswillcauseairtobedrawnintotheroomthroughthewater
heater’sventsystemcausingpoorcombustion.Sooting,serious
damagetothewaterheaterandtheriskoffireorexplosionmay
result.Itcanalsocreateariskofasphyxiation.
LOUVERS AND GRILLES
Thefreeareasofthefreshairopeningsintheinstructionsthatfollowdonot
takeintoaccountthepresenceoflouvers,grillesorscreensintheopenings.
Therequiredsizeofopeningsforcombustion,ventilationanddilution
airshallbebasedonthe“netfreearea”ofeachopening.Wherethe
freeareathroughadesignoflouverorgrilleorscreenisknown,itshall
beusedincalculatingthesizeofopeningrequiredtoprovidethefree
areaspecied.Wherethelouverandgrilledesignandfreeareaarenot
known,itshallbeassumedthatwoodlouverswillhave25%freearea
andmetallouversandgrilleswillhave75%freearea.Nonmotorized
louversandgrillesshallbexedintheopenposition.
FRESH AIR OPENINGS FOR CONFINED SPACES
The following instructions shall be used to calculate the size,
number and placement of openings providing fresh air for
combustion, ventilation and dilution in confined spaces. The
illustrationsshowninthissectionofthemanualareareference
for theopenings that provide fresh air into confined spaces
only.Donotrefertotheseillustrationsforthepurposeofvent
installation. See Venting Installation on page 14 for complete
ventinginstallationinstructions.
OUTDOOR AIR THROUGH TWO OPENINGS
FIGURE 8.
The confined space shall be provided with two permanent
openings,onecommencingwithin12inches(300mm)ofthetop
andonecommencingwithin12inches(300mm)ofthebottomof
the enclosure.The openings shall communicate directly with the
outdoors.SeeFigure8.
Eachopeningshallhaveaminimumfreeareaof1squareinchper
4,000Btu/hr(550mm2perkW)oftheaggregateinputratingofall
appliancesinstalledintheenclosure.Eachopeningshallnotbeless
than100squareinches(645cm2).
OUTDOOR AIR THROUGH ONE OPENING
FIGURE 9.
Alternatively a single permanent opening, commencing within 12
inches(300mm)ofthetopoftheenclosure,shallbeprovided.See
Figure9.Thewaterheatershallhaveclearancesofatleast1inch
(25mm)fromthesidesandbackand6inches(150mm)fromthe
frontoftheappliance.Theopeningshalldirectlycommunicatewith
theoutdoorsorshallcommunicatethroughaverticalorhorizontalduct
totheoutdoorsorspacesthatfreelycommunicatewiththeoutdoors
andshallhaveaminimumfreeareaofthefollowing:
1. 1 square inch per 3000 Btu/hr (733 mm
2
 per kW) of the total
inputratingofallapplianceslocatedintheenclosure,and
2. Notlessthanthesumoftheareasofallventconnectorsin
thespace.