e l e c t r i ch e a t e r sd u c topen coilfinned tubularexplosion-proof &corrosion resistantelectric heating and controls

IntroductionINDEECO designs and manufactures commercial and industrial electric heating and control systemsthat set the industry standard for excellence. The company’s heating solutions reflect more than75 years of innovation, product quality and efficient service. INDEECO’s innovation, PC HEAT , iscustom software that enables our representatives to respond to your requests for pricing and sizingof open coil and finned tubular duct heaters within minutes. With this software, your local INDEECOrepresentative becomes the source for certified prints, wiring diagrams — complete submittalinformation.Our heaters and controls range from the simplest standard duct heater to the most sophisticated,custom designed comprehensive system. INDEECO’s attention to detail and rigorous testing giveworldwide customers premium products that they receive quickly and at a fair market price.For your nearest INDEECO representative call 1-800-243-8162.

ContentsChoosing Open Coil or Finned Tubular DesignCustom Duct HeatersSpecific Requirements32Special Applications33Round Duct ConstructionDuct Heaters for Wet, Dusty and Corrosive Areas3435Bottom Mounted Terminal BoxInsulated Terminal Box35Pressure Plates3536Protective Screens36Unheated SectionsConstruction for Lined Ducts36Slip-and-Drive Construction3737Remote Panelboard37Minimum & Maximum Duct DimensionsOpen Coil Custom Heater – Sample Specification3940 Finned Tubular Custom Heater – Sample Specification334456677Calculating 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 Coil24 QUA Slip-in and QUZ Flanged Heaters24KW RatingsFrame Sizes2425Sizes and Maximum KW RatingsDetail Dimensions2626Voltage and PhaseControl Circuit Options & Special Features2626Number of Heating StagesSpecial Features27QUA/QUZ – Sample Specification31Explosion-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 Heaters51Standard Construction51Control OptionsInstallation51Custom Options5253How to Order53 Sample SpecificationCustom Explosion-proof Duct Heaters54555556ConstructionHow to OrderSample SpecificationTypical Wiring DiagramsLimited WarrantyINDEECO Products1www.indeeco.com800-243-8162

Choosing Open Coil or Finned Tubular DesignINDEECO manufactures both open coil (Figure 1)and finned tubular (Figure 2) heating elements andcan supply virtually any duct heater with either type ofelement. While most simple space heating applicationsuse the open coil design, there are many applicationswhere finned tubular construction is appropriate. Thefollowing are the significant advantages of each type ofconstruction.motor horsepower and makes it possible to retrofitopen coil heaters into existing systems withoutchanging the fan motor.Open CoilEconomy – On relatively small, low KW heaters (thebulk of typical space heating applications) the opencoil element is more economical. However, inlarge, high KW heaters, finned tubulars are moreeconomical due to lower manufacturing costs.Figure 1.Large Electrical Clearances – Generous electricalclearances between the coil and frame enableopen coils to withstand severe applications such assubway car heating, where voltages may exceed750 volts.Smaller Size – It is normally possible to get moreKW with open coil construction for a given face area.Only the highest Grade A resistance wire (80%nickel, 20% chromium) is used in all INDEECO ductheaters. This iron-free wire has a higher maximumoperating temperature, greater life, lower sag, lessresistance change and higher corrosion resistancethan other commonly used resistance wires.Finned TubularU-BentUsing calibrated tooling, the coils are mechanicallycrimped into stainless steel terminals. Thisconnection, along with 10-32 terminal threads andstainless steel connection hardware, insures cool,minimum resistance, trouble free terminations.An extended shank on the terminal places the criticalresistance coil-to-terminal connection well out intothe airstream to keep it cool even in applicationswhere up to 1” of interior insulation is used in theduct.Both terminal insulators and coil support insulatorsare fabricated from high-temperature ceramic. Theirdesign and method of installation enable them to: 1)absorb both mechanical and thermal loading withoutchipping or cracking and 2) easily withstand highvoltage dielectric tests.Element Temperature – The open coil elementreleases its heat directly into the airstream. As aresult, the open coil runs cooler than the coil in thefinned tubular element which is isolated from the airby insulation and a metal sheath.Low Pressure Drop – Because of the highpercentage of open space across the heater, opencoils have very low pressure drop as compared tofinned tubular heaters. This can result in reduced fanStraightTwo-PassFigure 2.Finned tubular elements are designed and built byINDEECO to meet the requirements of each job.Length, wattage, voltage and element style areengineered to give the most economical package.All elements consist of a Grade A coil (80% nickel,20% chromium), precisely centered in a stainlesssteel tube which is filled with granular magnesiumoxide. The entire assembly is compacted tomaximize both the heat transfer and dielectricproperties of the magnesium oxide. After compactionthe tube measures 0.475” (12 mm) O.D., anunusually large diameter providing sufficientinsulation for operation up to 600 volts.A stainless steel fin is helically wound onto the tubeto increase its heat transfer surface.INDEECO has standardized on stainless steel forits finned tubular elements because of its superiorresistance to moisture and corrosion.2www.indeeco.com800-243-8162

Specific RequirementsCalculating KW RequirementsSafety – Because the heating coil is completelyencased in a grounded metal sheath, shock hazarddue to accidental contact with the coil is eliminated.Heaters installed close to a register, grille, or accessdoor should either use finned tubular construction oran open coil unit with a protective screen.Airflow Contamination – If airborne contamination,such as dirt or dust, builds up on open coil elementsduring shutdown periods, 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 exposed todroplets of water in the airstream (e.g. immediatelydownstream from a spray type humidifier, a coolingcoil, or a fresh air intake) cannot short to ground asopen coils can when support bushings are wet.Once the volume of airflow (CFM – in cubic feet perminute) and the required temperature rise( T – in degrees F) through the heater are known,the required kilowatt rating (KW) of the heater canbe determined from the formula:KW CFM x T F3193(KW Liters/Second x T C837(Straight, Two-Pass and U-Bent elements arefurnished with mounting flanges, making themindividually removable through the terminal box.Where the desired heating capacity in BTU/Hr isknown, the KW is determined from the followingformula:KW BTU/Hr3412Serviceability – In the unlikely event of elementfailure, it is easier to replace individually mountedfinned tubular elements than open coil elements.Mechanical Stability – Finned tubular elements aremore rugged than open coils. They will withstandmore physical abuse.Airflow Uniformity – Finned tubular duct heaterstend to be more tolerant of nonuniform airflowconditions. Heat conducted along the elementlength reduces or eliminates hot spots resulting fromnonuniform airflow. With open coil heaters, it may benecessary to use a pressure plate to compensate forbad airflow conditions.Controllability – Because of their relatively highthermal inertia, finned tubular elements controlledwith on/off thermostat systems provide more precisecontrol. Furthermore, finned tubular elementscycle at a reduced rate, thus increasing the lifeof the power components such as contactors.Nevertheless, when SCR controllers are used,equally precise control can be obtained with eitherconstruction.Figure 3.Static Pressure DropStatic pressure drop through an open coil heater isquite low and, in most cases, can be ignored whencalculating system pressure drop. The pressure dropacross a finned tubular heater is greater than acrossan open coil. However, if pressure plates must beadded to an open coil, the pressure drop over theopen coil far exceeds the drop over a finned tubularheater. The curves in Figure 3 give data for all threeconstructions.3www.indeeco.com800-243-8162

Specific RequirementsMinimum VelocityElectric heaters differ from steam or hot water coilsin that the heat output is constant as long as theheater is energized. Therefore, sufficient airflow mustbe provided to prevent overheating and nuisancetripping of the thermal cutouts. The minimumrequired velocity is determined from Figure 4A or 4Bon the basis of entering air temperature and KW persquare foot of cross sectional duct area.1. Duct Area 24” x 12”/144 2 sq. ft.2. KW per square foot 10 KW/2 sq. ft. 5.3. Go to Figure 4B. Use top curve (below 80 F inletair).Find 5 KW per square foot on the vertical axis.Read minimum velocity required, which in thiscase is 310 feet per minute (FPM).4. Heater air velocity 1000 CFM/2 sq. ft. 500 FPM. Since 500 FPM exceeds the minimum, thisinstallation is safe. Consult your local INDEECOrepresentative for assistance if you do not havesufficient air velocity.The maximum air inlet temperature for open coilheaters is 100 F (38 C) and for finned tubularheaters is 80 F (27 C).Example: Determine whether the minimum airvelocity requirement is met for a 10 KW opencoil heater installed in a 24” wide x 12” high ductoperating with 1000 cubic feet per minute (CFM) ofair at a maximum inlet temperature of 65 F:Maximum VelocityHigh velocity airflow is not normally encounteredin typical commercial HVAC applications, wheninstalling open coil duct heaters into velocities over1200 feet per minute contact your local INDEECOrepresentative.32163028142412KW PER SQUARE FOOT DUCT AREA802220108690181681KW PER SQUARE FOOT DUCT AREA26149110012104FINNEDTUBULARCONSTRUCTION286OPEN COILCONSTRUCTION4200100 200 300 400 500 600 700 800 900 1000 1100 120000MINIMUM AIR VELOCITY REQUIRED100 200 300 400 500 600 700 800 900 1000 1100 1200MINIMUM AIR VELOCITY REQUIRED(FEET PER MINUTE)(FEET PER MINUTE)Figure 4A.Figure 4B.4www.indeeco.com800-243-8162

Specific RequirementsAirflow UniformityTo prevent hot spots, airflow must be uniformlydistributed across the heater face. Figure 5 illustratestypical heater misapplications which result in nonuniform airflow. The heater’s UL Listing requiresthat it not be installed closer than 4’ (122 cm)downstream or upstream from a fan outlet, abrupttransition, or other obstructions. Elbows or turnsmust be located at least 4’ (122 cm) from inlet of theheater and 2’ (61 cm) from outlet of the heater.If such an installation cannot be avoided, consultyour local INDEECO representative for assistance.We can provide a pressure plate, non-heated zonesor special low watt density coils to overcome theseproblems. Final approval of such applications is upto the local inspection authority.Heater too close to elbowHeater partially blocked by filter or frame memberHeater adjacent to transitionHeater too close to fanFigure 5.5www.indeeco.com800-243-8162

Specific RequirementsMultiple Heaters in the DuctClearanceINDEECO heaters are designed to be used singly,not in series in a duct. Since INDEECO heaters canbe furnished in virtually any size and KW rating,series installation of heaters can be avoided.For very large heaters, field installation and shippingmay be simplified by using two or more sectionsdesigned for parallel installation, illustrated byFigure 6. Each section, furnished in the flangeddesign, has individual thermal cutouts. Terminalblocks are provided to interconnect these cutouts inthe field. Sections rest stably one on top of the other.Heaters more than 6’ (152 cm) high are normallyprovided in sections, but larger single sectionheaters can be provided. Consult your localINDEECO representative for details.Figure 6.INDEECO heaters are UL Listed for zero clearanceto combustible surfaces. Thus, there is no minimumdistance between combustible materials and thesection of duct housing the heater, or the heateritself. However, the terminal box must be accessiblefor servicing. The NEC requires a minimumworkspace at least 30” (76 cm) wide by 42” (107 cm)deep for access to the heater terminal box. Morespace is required for large heaters and for removalof slip-in heaters which are over 42” long.In addition, sufficient clearance must be providedfo