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pl a n t h e Du c t wo r k inS t a l l a t i o n

WARNING

Toreducetheriskoffireandtoproperlyexhaust•
air,besuretoductairoutsidethehouseor building.
Donotventexhaustairintospaceswithin wallsor
ceilingsorintoattics,crawlspacesorgarages.
Tapeallductjointssecurely• topreventcombustion
by-products,smokeorodorsfromenteringthehome.
Doingsowillalsoimprovesystemefficiency.
Donotexhaustmorethanone• ventintoasingleduct.
Useonly• ductworkconstructedofmaterialsdeemed
acceptablebystate,municipalandlocalcodes.
Rangehoodsmayinterrupttheproperflowof•
smokeandcombustiongasesfromfurnaces,gas
waterheatersandfireplaces.Toavoiddrawing
lethalgasesintothehome,followthemanufactures
recommendationforthesedevicesandconsultNFPA
andASHRAErecommendations.
DO NOT• installanadditionalin-lineorexternal
blowertoincreasethelengthoftheduct run.Even
smalldifferencesbetweenblowerairflowratescan
greatlyreducetheairdrawbythehood.
Allductworkmaterials(includingscrewsandduct tape)•
mustbepurchasedseparatelybythecustomer.When
planningnewductwork,alwayslookforthe shortest,
mostdirectroutetotheoutside.
Thehoodexhaustconnectstoan8-inchround duct.•
Youcanincreasetheductsizeovertheductrunif
desired.Topreventabackdraft,neverdecreasethe
ductsizeovertherun.
Donotrelyonducttapealoneto sealductjoints.•
Fastenallconnectionswithsheetmetalscrewsand
tapealljointswithducttape.Usesheet metalscrews
asrequiretosupporttheductweight.
Topreventback-drafts,adamperattheductoutletmay•
alsoberequired.
Makesureductworkdoesnotinterferewith floorjoists•
orwallstuds.

Calculating the Maximum Duct Run Length

Themaximumstraightductlengthforthehood is100
feet.Foreachelbowandtransitionaddedto theduct
work,acertainnumberoffeetmustbe subtractedfrom
themaximumstraightlengthtocompensateforwind
resistance.Todeterminethelengththeductworkcannot
exceed,subtractalloftheequivalentlengthsof theelbows
andtransitionslistedbelowfrom100feet.

Duct Work Equivalent Lengths

DUCT PIECE SUBTRACT
90°elbow(8”Dia.) 7feet
45°elbow(8”Dia.) 3feet
31/4”x10”to8”round 4foot
Wallcapwithdamper 30feet
Roofcap 30feet

Duct Work Design Tips

Whereverpossible,reducethenumberoftransitions•
andturnstoasfewsharpanglesas possible.Two
staggered45°anglesarebetterthanone90°.
Keepturnsasfarawayfromthehood exhaustas•
possible,withasmuchspacebetweeneachbend as
possible.
Forbestperformance,useroundductinsteadof•
rectangular,especiallywhenelbowsarerequired.
Ifmultipleelbowsareused,trytokeep aminimumof•
24”(61cm)ofstraightductbetweenthem.
Avoid“S”or“backtoback”configurationsof adjacent•
elbows.
Inregionswheretheweathergetsextremelycold,•
thermalbreaks,suchasashortsectionof non-metallic
duct,shouldbeusedtoavoidindoorheat loss.The
breakshouldbelocatedasclosetothe passthrough
pointtotheoutsideaspossible.
Donotuseflexiblemetalduct.•
Donot• useductworkthatissmallerin cross-sectional
areathantherecommendedsizeduct(8”round).
pr e p a r i n g f o r in s T a l l a T i o n