Harman PF100 - Ducting Recommendations; Supply Air and Return Air Duct Sizing; Adding Air Conditioning

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3-90-08101R23_06/13
Adding Air Conditioning to the pellet furnace.
Aneasy ruleof thumbforA/C CFMblowersize is,.75 to
1CFMforeachsquarefootof conditionedspace.(std.8’
ceilingheight)
This furnace can be fitted with an air conditioning coil
mountedinthesupplyairplenum.
HHT is not responsible for sizing, duct placement, or
interconnections.HoweverwehavemadeaddingA/Ctothe
furnaceeasierwiththeinformationlistedbelow.
Thereisafactoryinstalledjunctionboxreadytoacceptyour
A/Crelay.TheA/Cfancontrolcenterwith40vatransformer
musthaveaDPDTrelay.WhiteRodgers#90-112,part#
3-20-38056isavailable.Otherbrandsarealsoacceptable
foruse.
ThewiringshouldbedoneasperFig.34.Thelowvoltage
wiring to the outside condensing unit and the cooling
thermostatarenotshown.Seecondensingunitdiagrams
forthatinformation.
Thisstyleofrelayisusedtolockoutthefeedersystemofthe
pelletfurnacewhentheA/Cunitiscallingforcooling.This
isafail-safeagainstbothunitsoperatingatthesametime.
SeetheNOTEinthelowerleftcorner.
Recommendations for Supply Air and Return Air duct
sizing.
Thespeedorvelocityofairmovingthroughductsystems
increasesastheductdecreasesinsizewiththesameCFM
blower.Thesoundofairowingthroughtheductincreases
as the velocity increases. Therefore the largest duct size
practialshouldbeused.
Thevelocitytosoundlevelmustbetakenintoconsideration
whenconnectingthisfurnaceintoanexistingductsystem.
Asaprimarysourcefurnacetheductsystemcanbeinstalled
totthecustomersneeds.
ThesearerecommendedSupplyAirductsizes(insquare
inches)forsomeofthedifferentCFMblowersthatmaybe
usedwiththisfurnace.
Velocity 500fpm 700fpm 900fpm
Static-In. W.C. .3Minimumto.6Maximum
1000cfm. 270in²  210in²  160in²
1450cfm 360in²  290in² 220in²
1638cfm 470in²  360in²  290in²
(Theseductsizesareonlyrecommendations.)
TheReturnAirductsystemshouldbesizedaproximately10
percentlargerforheatingonlysystemsand20percentlarger
ifairconditioningisinstalled.
Installing Duct
NOTE:
It is highly recomended that the furnace
control be turned to the “OFF” position
whenever air conditioning is being used,
whetherornotitisinterconnected.
CAUTION: Regardlessofthesupplyairduct
sizeinstalled,theDistributionBlowerMotor
MUST be checked for runningAmperage.
Checkthemotornameplateforthefullload
AMPS.Iftheamperageisrunninghigherthan
thatlisted,asupplyairrestrictingdampermay
be required to increase the supply plenum
positivestaticpressure.
Fig.34