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CommercialDuct HeatersOur products do more in a widerange of applications. Expect More.

IntroductionIndeeco designs and manufactures commercial and industrial electric heatingand control systems that set the industry standard for excellence. Thecompany’s heating solutions reflect more than 85 years of innovation, productquality and efficient service. Indeeco’s innovation, PC HEAT , is customsoftware that enables our representatives to respond to your requests forpricing and sizing of open coil and finned tubular duct heaters within minutes.With this software, your local Indeeco representative becomes the source forcertified prints, wiring diagrams — complete submittal information.Our heaters and controls range from the simplest standard duct heater tothe most sophisticated, custom designed comprehensive system. Indeeco’sattention to detail and rigorous testing give worldwide customers premiumproducts that they receive quickly and at a fair market price.

ContentsChoosing Open Coil or Finned Tubular DesignSpecific Requirements334456677Calculating KW RequirementsStatic Pressure DropMinimum VelocityMaximum VelocityAirflow UniformityMultiple Heaters in the DuctClearanceUL and NEC RequirementsInternational RequirementsInstallation Information88Heater InstallationField WiringStandard Control Options1010101112Internal WiringControl Option G — BasicControl Option J — PneumaticControl Option K — ProportionalThermostatsConstruction – allic Thermal CutoutsLinear Thermal CutoutsAirflow SwitchFan RelayMagnetic ContactorsFusesControl TransformerDisconnect SwitchPilot LightsPilot SwitchPneumatic/Electric (PE) SwitchesElectronic ControlsSCR Power ControllersStep Controllers (Sequencers)Step Controllers (Microprocessor-based)Vernier Proportional ControlThermostats/Inputs for Electronic ControlsConstruction – Mechanical22222223Slip-in HeatersFlanged HeatersZero Clearance ConstructionPhysical StandardsStandard Duct Heaters – Open Coil24242425262626262731QUA Slip-in and QUZ Flanged HeatersKW RatingsFrame SizesSizes and Maximum KW RatingsDetail DimensionsVoltage and PhaseControl Circuit Options & Special FeaturesNumber of Heating StagesSpecial FeaturesQUA/QUZ – Sample SpecificationCustom Duct Heaters3233343535353636363737373940Special ApplicationsRound Duct ConstructionDuct Heaters for Wet, Dusty and Corrosive AreasBottom Mounted Terminal BoxInsulated Terminal BoxPressure PlatesProtective ScreensUnheated SectionsConstruction for Lined DuctsSlip-and-Drive ConstructionRemote PanelboardMinimum & Maximum Duct DimensionsOpen Coil Custom Heater – Sample SpecificationFinned Tubular Custom Heater – Sample SpecificationExplosion-proof Duct plete Product LineApplicationsUse of Electric Heaters in Hazardous AreasNational Electrical Code ClassificationClassDivisionGroupEngineering InformationAirflow RequirementsComparison ChartULTRA-SAFE Explosion-proof Duct Heaters46464748495050Standard ConstructionInstallationTemperature ControlStandard Heater ListingCustom OptionsHow to OrderSample SpecificationSeries EP2 Explosion-proof Duct Heaters515151525353Standard ConstructionControl OptionsInstallationCustom OptionsHow to OrderSample SpecificationCustom Explosion-proof Duct Heaters54555556ConstructionHow to OrderSample SpecificationTypical Wiring DiagramsLimited WarrantyMore Indeeco Productswww.indeeco.com800-243-81621

Choosing Open Coil or Finned TubularDesignIndeeco manufactures both open coil (Figure 1) and finnedtubular (Figure 2) heating elements and can supply virtually anyduct heater with either type of element. While most simple spaceheating applications use the open coil design, there are manyapplications where finned tubular construction is appropriate.The following are the significant advantages of each type ofconstruction.Open CoilLarge Electrical Clearances – Generous electrical clearancesbetween the coil and frame enable open coils to withstandsevere applications such as subway car heating, where voltagesmay exceed 750 volts.Economy – On relatively small, low KW heaters (thebulk of typical space heating applications) the open coil elementis more economical. However, in large, high KW heaters, finnedtubulars are more economical due to lower manufacturing costs.Smaller Size – It is normally possible to get more KW with opencoil construction for a given face area.Finned TubularTwo-passFigure 1.Only the highest Grade A resistance wire (80% nickel, 20%chromium) is used in all Indeeco duct heaters. This iron-free wirehas a higher maximum operating temperature, greater life, lowersag, less resistance change and higher corrosion resistance thanother commonly used resistance wires.Using calibrated tooling, the coils are mechanically crimpedinto stainless steel terminals. This connection, along with 10-32terminal threads and stainless steel connection hardware,insures cool, minimum resistance, trouble free terminations.An extended shank on the terminal places the critical resistancecoil-to-terminal connection well out into the airstream to keep itcool even in applications where up to 1” of interior insulation isused in the duct.Both terminal insulators and coil support insulators arefabricated from high-temperature ceramic. Their designand method of installation enable them to: 1) absorb bothmechanical and thermal loading without chipping or crackingand 2) easily withstand high voltage dielectric tests.Element Temperature – The open coil element releases its heatdirectly into the airstream. As a result, the open coil runs coolerthan the coil in the finned tubular element which is isolated fromthe air by insulation and a metal sheath.Low Pressure Drop – Because of the high percentage of openspace across the heater, open coils have very low pressuredrop as compared to finned tubular heaters. This can result inreduced fan motor horsepower and makes it possible to retrofitopen coil heaters into existing systems without changing the fanmotor.2U-BentStraightFigure 2.Finned tubular elements are designed and built by Indeeco tomeet the requirements of each job. Length, wattage, voltageand element style are engineered to give the most economicalpackage.All elements consist of a Grade A coil (80% nickel, 20%chromium), precisely centered in a stainless steel tube whichis filled with granular magnesium oxide. The entire assemblyis compacted to maximize both the heat transfer and dielectricproperties of the magnesium oxide. After compaction the tubemeasures 0.475” (12 mm) O.D., an unusually large diameterproviding sufficient insulation for operation up to 600 volts.A stainless steel fin is helically wound onto the tube to increaseits heat transfer surface.Indeeco has standardized on stainless steel for its finned tubularelements because of its superior resistance to moisture andcorrosion.Straight, Two-Pass and U-Bent elements are furnished withmounting flanges, making them individually removable throughthe terminal box.www.indeeco.com800-243-8162

Specific RequirementsSafety – Because the heating coil is completely encased ina grounded metal sheath, shock hazard due to accidentalcontact with the coil is eliminated. Heaters installed close to aregister, grille, or access door should either use finned tubularconstruction or an open coil unit with a protective screen.Where the desired heating capacity in BTU/Hr is known, the KWis determined from the following formula:KW BTU/Hr3412Airflow Contamination – If airborne contamination, such asdirt or dust, builds up on open coil elements during shutdownperiods, the elements can short out. Finned tubular elements,with their insulated coils, eliminate this problem. Furthermore,upon start-up, a finned tubular heater which has been exposedto droplets of water in the airstream (e.g. immediatelydownstream from a spray type humidifier, a cooling coil, or afresh air intake) cannot short to ground as open coils can whensupport bushings are wet.Serviceability – In the unlikely event of element failure, it iseasier to replace individually mounted finned tubular elementsthan open coil elements.Mechanical Stability – Finned tubular elements are morerugged than open coils. They will withstand more physical abuse.Airflow Uniformity – Finned tubular duct heaters tend to bemore tolerant of nonuniform airflow conditions. Heat conductedalong the element length reduces or eliminates hot spotsresulting from nonuniform airflow. With open coil heaters, itmay be necessary to use a pressure plate to compensate for badairflow conditions.Controllability – Because of their relatively high thermal inertia,finned tubular elements controlled with on/off thermostatsystems provide more precise control. Furthermore, finnedtubular elements cycle at a reduced rate, thus increasing thelife of the power components such as contactors. Nevertheless,when SCR controllers are used, equally precise control can beobtained with either construction.Calculating KW RequirementsOnce the volume of airflow (CFM – in cubic feet per minute) andthe required temperature rise( T – in degrees F) through theheater are known, the required kilowatt rating (KW) of the heatercan be determined from the formula:CFM x T F3193KW (Liters/Second x T C837(KW Figure 3.Static Pressure DropStatic pressure drop through an open coil heater is quite lowand, in most cases, can be ignored when calculating systempressure drop. The pressure drop across a finned tubular heateris greater than across an open coil.However, if pressure plates must be added to an open coil, thepressure drop over the open coil far exceeds the drop over afinned tubular heater. The curves in Figure 3 give data for allthree constructions.www.indeeco.com800-243-81623

Specific RequirementsMinimum VelocityElectric heaters differ from steam or hot water coils in thatthe heat output is constant as long as the heater is energized.Therefore, sufficient airflow must be provided to preventoverheating and nuisance tripping of the thermal cutouts. Theminimum required velocity is determined from Figure 4A or 4Bon the basis of entering air temperature and KW per square footof cross sectional duct area.The maximum air inlet temperature for open coil heaters is 100 F(38 C) and for finned tubular heaters is 80 F (27 C).Example: Determine whether the minimum air velocityrequirement is met for a 10 KW open coil heater installed in a 24”wide x 12” high duct operating with 1000 cubic feet per minute(CFM) of air at a maximum inlet temperature of 65 F:1.2.3.4.Duct Area 24” x 12”/144 2 sq. ft.KW per square foot 10 KW/2 sq. ft. 5.Go to Figure 4B. Use top curve (below 80 F inlet air).Find5 KW per square foot on the vertical axis. Read minimumvelocity required, which in this case is 310 feet per minute(FPM).Heater air velocity 1000 CFM/2 sq. ft. 500 FPM.Since 500 FPM exceeds the minimum, this installation is safe.Consult your local Indeeco representative for assistance ifyou do not have sufficient air velocity.Maximum VelocityHigh velocity airflow is not normally encountered in typicalcommercial HVAC applications, when installing open coil ductheaters into velocities over 1200 feet per minute contact yourlocal Indeeco CTION22018 -910221681KW PER SQUARE FOOT DUCT AREAKW PER SQUARE FOOT DUCT AREA12BELOW800 ININLELETATIRAIR261491 -0 10INTLEAIR121086OPEN COILCONSTRUCTION4200100 200 300 400 500 600 700 800 900 1000 1100 120000MINIMUM AIR VELOCITY REQUIRED(FEET PER MINUTE)(FEET PER MINUTE)Figure 4A.4100 200 300 400 500 600 700 800 900 1000 1100 1200MINIMUM AIR VELOCITY REQUIREDFigure 4B.www.indeeco.com800-243-8162

Specific RequirementsAirflow UniformityTo prevent hot spots, airflow must be uniformly distributedacross the heater face. Figure 5 illustrates typical heatermisapplications which result in non-uniform airflow. The heater’sUL Listing requires that it not be installed closer than 4’ (122 cm)downstream or upstream from a fan outlet, abrupt transition, orother obstructions. Elbows or turns must be located at least 4’(122 cm) from inlet of the heater and 2’ (61 cm) from outlet of theheater.Heater too close to elbowHeater adjacent to transitionIf such an installation cannot be avoided, consult your localIndeeco representative for assistance. We can provide a pressureplate, non-heated zones or special low watt density coils toovercome these problems. Final approval of such applications isup to the local inspection authority.Heater partially blocked byfilter or frame memberHeater too close to fanFigure 5.www.indeeco.com800-243-81625

Specific RequirementsMultiple Heaters in the DuctClearanceIndeeco heaters are not designed for series installation in asingle duct. Since Indeeco heaters can be furnished in virtuallyany size and KW rating, series installation of heaters can beavoided.Indeeco heaters are UL Listed for zero clearance to combustiblesurfaces. Thus, there is no minimum distance betweencombustible materials and the section of duct housing theheater, or the heater itself. However, the terminal box must beaccessible for servicing. The NEC requires a minimum workspaceat least 30” (76 cm) wide by 42” (107 cm) deep for access to theheater terminal box. More space is required for large heaters andfor removal of slip-in heaters which are over 42” long.For very large heaters, field installation and shipping may besimplified by using two or more sections as illustrated by Figure6. Each section, furnished in the flanged design, has its ownset of thermal limit controls. Terminal blocks are provided tointerconnect these cutouts in the field. Sections rest stably oneon top of the other.Heaters more than 6’ (152 cm) high are normally provided insections, but larger single section heaters can be provided.Consult your local Indeeco representative for details.In addition, sufficient clearance must be provided for convectioncooling of all heaters with built-in SCR power controllers (