11
Unconned Space
Anunconned space has a minimum total air volume of
50cu.ft. (cubic feet) for each 1,000 Btu/Hr input rating of all
appliancesinthe total space (cu.ft. = length x width x height
ofspace). Include adjoining rooms only if there are doorless
passagewaysorventilationgrillsbetweentherooms.IftheBtu
per50 cu.ft. is less than 1,000 Btu/Hr, then fresh air will be
providedbythenaturalairowintothehouse.
Conned Space
 Aconnedspacehasanairvolumeoflessthan50cu.ft.for
each1,000Btu/Hrinputratingofallappliancesinthespace(cu.
ft.=lengthxwidthxheightof space).Includeadjoiningrooms
onlyif there are door less passageways or ventilation grills
betweentherooms.
Determining Total Air Volume
Usethis work sheet to determine if you have a conned
orunconnedspace.Thespacetobeconsideredincludes not
onlytheroominwhichyouwillinstallthereplacebutalsoany
adjoiningrooms with ventilation grills between them or door
lesspassageways.
1. Determinethetotalvolumeofyourspace
 LxWxH=_______cu.ft.
 Example:Spacesize= 20ft.longx 20ft.widex 8ft.high
(ceilingheight)=3,200cu.ft.
Ifadjoiningventilation to adjoining room is supplied with
grillsoropenings,addthevolumeoftheseroomstothetotal
volumeofthespace.
2. Divide the space volume by 50 cu.ft. to determine the
maximumBtu/Hrthespacecansupport.
 _______cu.ft.(volumeofspace)
 50cuft.=(MaximumBtu/Hrthespacecansupport)
 Example:3200cuft.(Volumeofspace)/50cu.Ft.=64.0or
64,000(maximumBtu/Hrthespacecansupport.)
3. AddtheBtu/Hrofallfuelburningappliancesinthespace.
Vent-freereplace _______ Btu/hr
Gaswaterheater*  _______ Btu/hr
Gasfurnace _______ Btu/hr
Ventedgasheater _______ Btu/hr
Gasreplacelogs  _______ Btu/hr
Othergasappliances* _______ Btu/hr
Total= _______ Btu/hr
Example: Gaswaterheater40,000Btu/hr
  Vent-freereplace+36,000Btu/hr
  Total=76,000Btu/hr
*Donotincludedirect-ventedgasappliances.Directventdraws
combustionairfromtheoutdoorsandventstotheoutdoors.
4. Comparethemaximum Btu/Hrthespacecan supportwith
theactualamountofBtu/Hrused.
 _________Btu/Hr(maximumthespacecansupport)
 _________Btu/Hr(actualamountofBtu/Hrused)
 Example:
 64,000Btu/Hr(maximumthespacecansupport)
 76,000Btu/Hr(actualamountofBtu/Hrused)
 Thespacein thepreviousexamplewas aconnedspace
becausetheactualBtu/Hr usedwasmore thanthemaximum
Btu/Hrthespacecouldsupport.IfyoundyouhaveaConned
Space,youmustprovide additional���freshair.Youroptionsare
asfollows:
a)Re-workworksheet,addingthespace ofanadjoiningroom
thatmaynothavequaliedfortheextravolume.Iftheextra
spaceprovides enough volume to convert the area to an
unconnedspace, remove door to adjoining room or add
ventilationgrillsbetweenrooms.
b)Ventroomdirectlytotheoutdoors.
c)Install a lower Btu/Hr gas log (if lower Btu/Hr size makes
roomunconned).
IftheactualBtu/Hr usedislessthanthe maximumBtu/Hrthe
spacecansupport,thespaceisanunconnedspace. Youwill
neednoadditionalfreshairventilation.
WARNING:Ifthe area in which the heater may be operated
issmaller than that dened as an unconned space, provide
adequatecombustionandventilationairbyoneofthemethods
describedintheNationalFuelGasCode,ANSIZ223.1Section
5.3orapplicablelocalcodes.
Localcodes may have stricter denitions for conned space
and/orfor unusually tight construction. Installing our optional
outsideairkitmayallowthespacetobeclassiedasnotbeing
unusuallytightorbeinganunconnedspace. Checkyoulocal
codes.
IMPORTANT:Do not provide openings for inlet or outlet air
intoanatticiftheattichasathermostat-controlledpower vent.
Heatedairenteringtheatticwillactivatethepowervent.