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Provisionfor combustionand ventilation air must be in accordance with Section 5.3, Air for Combustionand Ventilation, of
the National Fuel Gas Code, ANSI Z223.1-1atest revision, or applicable provisionsof the local building codes.
WARNING
Be sure to provide enough fresh air for combustion.
Enough air insures proper combustion and assures that
no hazard will develop due to the lack of oxygen.
NOTE
If you use a fireplace or a kitchen or bathroom exhaust
fan, you should install an outside air intake. These
devices will rob the boiler and water heater of combus-
tion air.
Youmustprovideforenoughfreshairtoassurepropercombustion.Thefire
in theboilerusesoxygen,it musthavea continuoussupply.Theair in a
housecontainsonlyenoughoxygentosupplytheburnerfora shorttime.
Outsideair mustenterthehouseto replacethatusedbytheburner.Study
followingexamples1and2 todetermineyourfreshair requirements.
EXAMPLE1: BoilerLocatedin UnconfinedSpace
An unconfinedspaceis definedasa spacewhosevolumeis notlessthan
50cubicfeetper!,000 Btuperhourofthetotalinputratingofall appliances
installedinthatspace.
Ifyourboileris inan openarea(unpartitionedbasement)inaconventional
house,theairthatleaksthroughthecracksarounddoorsandwindowswill
usuallybeadequateto provideairforcombustion.Thedoorsshouldnotfit
tightly.Donotcaulkthecracksaroundthewindows.
Equipmentlocatedinbuildingsofunusuallytightconstructionshallbepro-
videdwithair forcombustion,ventilation,anddiMion offluegasesusing
themethodsdescribedin example2Bor shallbespeciallyengineered.The
authorityhavingjurisdictionmustapprovespeciallyengineeredinstalla-
tions.
EXAMPLE2: BoilerLocatedin ConfinedSpace
A.All Air from Inside the Building:Theconfinedspaceshallbepro-
videdwithtwopermanentopeningscommunicatingdirectlywithanaddi-
tionalroom(s)of sufficientvolumeso thatthecombinedvolumeofall
spacesmeetsthecriteriafor anunconfinedspace.Thetotalinputofall
gasutilizationequipmentinstalledin thecombinedspaceshallbecon-
sideredin makingthis determination.Eachopeningshallhavea mini-
mumfreeareaofonesquareinchper1,000Btuperhourofthetotalinput
ratingol all gasutilizationequipmentin theconfinedspace,butnotless
that100squareinches.Oneopeningshallbewithin12inchesofthetop
andonewithin12 inchesof thebottomoftheenclosure.Theminimum
dimensionofairopeningsshallnotbelessthan3 inches.
B,All Airfrom Outdoors:Theconfinedspaceshallcommunicatewiththe
outdoorsin accordancewithmethods1or 2.Theminimumdimensionof
air openingsshallnotbelessthan3 in.Whereductsareused,theyshall
beofthesamecross-sectionalareaasthefreeareaof theopeningsto
whichtheyconnect.
1.Twopermanentopenings,one commencingwithin 12 inchesofthe
top,andonecommencingwithin12inchesolthebottom,oftheenclo-
sureshallbeprovided.Theopeningsshallcommunicatedirectly,or by
theducts,withtheoutdoorsor spaces(crawlor attic)thatfreelycom-
municatewith theoutdoors,
a)Wheredirectlycommunicatingwiththeoutdoorsor wherecommu-
nicatingto theoutdoorsthroughverticalducts,eachopeningshall
haveaminimumfreeareaof1 sq.in.per4000Btuperhouroftotal
inputratingofagequipmentin theenclosure.(SeeFigure3A.)
b)Wherecommunicatingwiththeoutdoorsthroughhorizontalducts,
eachopeningshallhavea minimumfreeareaof1 sq, in.per2000
Btuperhouroftotalinputratingol all equipmentin theenclosure.
(SeeFigure3B.)
2. Onepermanentopeningcommencingwith 12inchesofthetopof the
enclosure,shallbepermittedwheretheequipmenthasclearanceofat
least1 inchfromthesidesandbackand6 inchesfromthefrontofthe
appliance,Theopeningshaddirectlycommunicatewith theoutdoors
or shallcommunicatethrougha verticalor horizontalducttotheout-
doorsorspaces(crawlor attic)thatfreelycommunicatewiththeout-
doors,andshallhaveaminimumfreeareaof:
a)1 sq,inchper3000Btuperhourofthetotalinpulol all equipment
locatedintheenclosure(SeeFigure4),and
b)Notlessthanthesumoftheareasofall venlconnectorsin thecon-
finedspace.
I Figure 3A - FRESH AIR DUCT CAPACITIES (Btuh)
1 Square Inch per 4,000 Btuh
100% Free 75% Free 25% Free
Area Area Area
Fresh Air 1/4"Wire Metal Wood
Duct Size Mesh Louvers Louvers
3" x 12" 144,000 108,000 36,000
8" x 8" 256,000 192,000 64,000
8" x 12" 384,000 288,000 96,000
81/2"x 16" 512,000 384,000 128,000
I Figure 3B - FRESH AIR DUCT CAPACITIES (Btuh)
1 Square Inchper 2,000 Btuh
100% Free 75% Free 25% Free
Area Area Area
Fresh Air 1/4"Wire Metal Wood
Duct Size Mesh Louvers Louvers
3" x 12" 72,000 54,000 18,000
8" x 8" 128,000 96,000 32,000
8" x 12" 192,000 144,000 48,000
81/2"x 16" 256,000 192,000 64,000
I Figure 4 - FRESH AiR DUCT CAPACITIES (Btuh)
1 Square Inch per 3,000 6tuh
100% Free 75% Free 25% Free
Area Area Area
Fresh Air %" Wire Metal Wood
Duct Size Mesh Louvers Louvers
3" x !2" 108,000 81,000 27,000
8" x 8" 192,000 144,000 48,000
8" x 12" 288,000 216,000 72,000
81/2"x 16" 384,000 288,000 96,000
7,_4 5
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