Instruction manual
13
amountofcombustionaircanresultinareorexplosionandcauseproperty
damage,seriousbodilyinjuryordeath.
UNCONFINED SPACE
AnUnconfinedSpaceisonewhosevolumeisnotlessthan50
cubic feet per 1,000 Btu/hr (4.8 cubic meters per kW) of the
totalinputratingofallappliancesinstalledinthespace.Rooms
communicatingdirectlywiththespace,inwhichtheappliances
are installed, through openings not furnished with doors, are
consideredapartoftheunconfinedspace.
Makeupairrequirementsfortheoperationofexhaustfans,kitchen
ventilationsystems, clothes dryersandfireplaces shall alsobe
considered in determining the adequacy of a space toprovide
combustion,ventilationanddilutionair.
UNUSUALLY TIGHT CONSTRUCTION
Inunconfinedspacesinbuildings,infiltrationmaybeadequateto
provideairforcombustion,ventilationanddilutionoffluegases.
However,inbuildingsofunusuallytightconstruction(forexample,
weatherstripping,heavilyinsulated,caulked,vaporbarrier,etc.)
additionalairmustbeprovidedusingthemethodsdescribedin
theConfinedSpacesectionthatfollows.
CONFINED SPACE
AConnedSpaceisonewhosevolumeislessthan50cubicfeetper
1,000Btu/hr(4.8cubicmetersperkW)ofthetotalinputratingofall
appliancesinstalledinthespace.
Openingsmustbeinstalledtoprovidefreshairforcombustion,ventilation
and dilution in conned spaces. The requiredsize for the openings is
dependentonthemethodusedtoprovidefreshairtotheconnedspace
andthetotalBtu/hrinputratingofallappliancesinstalledinthespace.
DIRECT VENT APPLIANCES
Appliances installed in a Direct Vent conguration that derive all
air for combustion from the outdoor atmospherethrough sealed
intakeairpipingarenotfactoredinthetotalapplianceinputBtu/hr
calculationsusedtodeterminethesizeofopeningsprovidingfresh
airintoconnedspaces.
EXHAUST FANS
Whereexhaustfansareinstalled,additionalairshallbeprovided
toreplacetheexhaustedair.Whenanexhaustfanisinstalledin
thesamespacewithawaterheater,sufficientopeningstoprovide
freshairmustbeprovidedthataccommodatetherequirements
forallappliancesintheroomandtheexhaustfan.Undersized
openingswillcauseairtobedrawnintotheroomthroughthewater
heater’sventsystemcausingpoorcombustion.Sooting,serious
damagetothewaterheaterandtheriskoffireorexplosionmay
result.Itcanalsocreateariskofasphyxiation.
LOUVERS AND GRILLES
Thefreeareasofthefreshairopeningsintheinstructionsthatfollowdonot
takeintoaccountthepresenceoflouvers,grillesorscreensintheopenings.
Therequiredsizeofopeningsforcombustion,ventilationanddilution
airshallbebasedonthe“netfreearea”ofeachopening.Wherethe
freeareathroughadesignoflouverorgrilleorscreenisknown,itshall
beusedincalculatingthesizeofopeningrequiredtoprovidethefree
areaspecied.Wherethelouverandgrilledesignandfreeareaarenot
known,itshallbeassumedthatwoodlouverswillhave25%freearea
andmetallouversandgrilleswillhave75%freearea.Nonmotorized
louversandgrillesshallbexedintheopenposition.
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
illustrationsshowninthissectionofthemanualareareference
for the openingsthat provide freshair into confined spaces
only.Donotrefertotheseillustrationsforthe purpose ofvent
installation. See Venting Installation on page 18 for complete
ventinginstallationinstructions.
OUTDOOR AIR THROUGH TWO OPENINGS
FIGURE 8.
The confined space shall be provided with two permanent
openings,onecommencingwithin12inches(300mm)ofthetop
andonecommencingwithin12inches(300mm)ofthebottomof
the enclosure. The openingsshall communicate directlywith the
outdoors.SeeFigure8.
Eachopeningshallhaveaminimumfreeareaof1squareinchper
4,000Btu/hr(550mm2perkW)oftheaggregateinputratingofall
appliancesinstalledintheenclosure.Eachopeningshallnotbeless
than100squareinches(645cm2).
OUTDOOR AIR THROUGH ONE OPENING
FIGURE 9.
Alternatively a single permanent opening, commencing within 12
inches(300mm)ofthetopoftheenclosure,shallbeprovided.See
Figure9.Thewaterheatershallhaveclearancesofatleast1inch
(25mm)fromthesidesandbackand6inches(150mm)fromthe
frontoftheappliance.Theopeningshalldirectlycommunicatewith
theoutdoorsorshallcommunicatethroughaverticalorhorizontalduct
totheoutdoorsorspacesthatfreelycommunicatewiththeoutdoors
andshallhaveaminimumfreeareaofthefollowing:
1. 1 square inch per 3000 Btu/hr (733mm
2
per kW) of the total
inputratingofallapplianceslocatedintheenclosure,and
2. Notlessthanthesumoftheareasofallventconnectorsin
thespace.