A.O. Smith Gphe 50 Instruction Manual - page 12
12
Such a condition often will result in a yellow, luminous burner
flame, causing sooting of the combustion chamber, burners and
flue tubes and creates a risk of asphyxiation.
Do not install the water heater in a confined space unless an
adequate supply of air for combustion and ventilation is brought in
tothatspaceusingthemethodsdescribedintheConfinedSpace
section that follows.
Neverobstructtheflowofventilationair.Ifyouhaveanydoubtsor
questions at all, call your gas supplier. Failure to provide the proper
amountofcombustionaircanresultinafireorexplosionandcause
property damage, serious bodily injury or death.
unconfIned space
AnUnconfinedSpaceisonewhosevolumeisnotlessthan50cubic
feetper1,000Btu/hr(4.8cubicmetersperkW)ofthetotalinput
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
unconfinedspace.
Makeup air requirements for the operation of exhaust fans, kitchen
ventilationsystems,clothesdryersandfireplacesshouldalsobe
considered in determining the adequacy of a space to provide
combustion, ventilation and dilution air.
unusuallY tIGht constructIon
Inunconfinedspacesinbuildings,infiltrationmaybeadequateto
provideairforcombustion,ventilationanddilutionoffluegases.
However,inbuildingsofunusuallytightconstruction(forexample,
weather stripping, heavily insulated, caulked, vapor barrier, etc.)
additional air must be provided using the methods described in the
ConfinedSpacesectionthatfollows.
confIned space
AConfinedSpaceisonewhosevolumeislessthan50cubicfeet
per1,000Btu/hr(4.8cubicmetersperkW)ofthetotalinputrating
of all appliances installed in the space.
Openings must be installed to provide fresh air for combustion,
ventilationanddilutioninconfinedspaces.Therequiredsizeforthe
openings is dependent on the method used to provide fresh air to
theconfinedspaceandthetotalBtu/hrinputratingofallappliances
installed in the space.
dIrect vent applIances
Appliances installed in a Direct Ventconfiguration thatderive 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
airintoconfinedspaces.
eXhaust fans
Where exhaust fans are installed, additional air should be provided
to replace the exhausted air. When an exhaust fan is installed in
thesamespacewithawaterheater,sufficientopeningstoprovide
fresh air must be provided that accommodate the requirements for
all appliances in the room and the exhaust fan. Undersized openings
willcauseairtobedrawnintotheroomthroughthewaterheater’s
vent system causing poor combustion. Sooting, serious damage to
thewaterheaterandtheriskoffireorexplosionmayresult.Itcan
also create a risk of asphyxiation.
louvers and GrIlles
The free areas of fresh air openings in instructions that follow do not take
in to account presence of louvers, grilles or screens in openings.
The required size of openings for combustion, ventilation and dilution
airshouldbebasedonthe“netfreearea”ofeachopening.Where
the free area through a design of louver or grille or screen is known, it
should be used in calculating the size of opening required to provide the
freeareaspecified.Wherethelouverandgrilledesignandfreearea
are not known, it should be assumed that wood louvers will have 25%
free area and metal louvers and grilles will have 75% free area. Non
motorizedlouversandgrillesshouldbefixedintheopenposition.
fresh aIr openInGs for confIned spaces
The following instructions should be used to calculate the size,
number and placement of openings providing fresh air for combustion,
ventilationanddilutioninconfinedspaces.Theillustrationsshownin
this section of the manual are a reference for the openings that provide
freshairintoconfinedspacesonly.Donotrefertotheseillustrations
for the purpose of vent installation. See Installation of Vent System on
pages 18-27 for complete venting installation instructions.
outdoor aIr throuGh two openInGs
fIGure 6.
The confined space should be provided with two permanent
openings,onecommencingwithin12inches(300mm)ofthetop
andonecommencingwithin12inches(300mm)ofthebottomof
the enclosure. The openings should communicate directly with
the outdoors. See Figure 6.
Each opening should have a minimum free area of 1 square inch
per4,000Btu/hr(550mm
2
perkW)oftheaggregateinputrating
of all appliances installed in the enclosure. Each opening should
notbelessthan100squareinches(645cm
2
).
outdoor aIr throuGh one openInG
fIGure 7.
Alternatively a single permanent opening, commencing within 12
inches(300mm)ofthetopoftheenclosure,shouldbeprovided.See