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    Electric Heaters
    Cartridge Insertion Heaters Circulation Heaters Immersion Heaters Air Heaters Flexible Heaters Tubular Heaters Gas Delivery and Exhaust Heaters High-Temperature Heaters Specialty Heaters View All
    Temperature & Process Control
    Multi Loop Controllers Single Loop Controllers Indicators and Alarms Limits and Scanners Operator Interfaces
    Power Control
    Power Controllers Power Switches
    Data Management
    Data Recorders
    Panels & Systems
    WATCONNECT® Control Panels POWERSAFE™ Thermal System
    Sensors
    Thermocouples Resistance Temperature Detectors (RTDs) Fiber Optic Sensing
    man with dual monitors using product selection assistant
    Not Sure? Try Our Digital Product Assistant

    Take the complexity out of product selection with our innovative Digital Product Assistant. Answer a few application questions and our interactive tool will recommend a product from our catalog.

    Launch Assistant

    Services

    thermalwatch thumbnail image of laptop with modern analytics dashboard
    THERMALWATCH™ Intelligent Analytics Solution

    THERMALWATCH leverages our deep understanding of thermal systems to provide secure data integration and management, along with expert analysis, to transform data into valuable information.

    Learn More

    Configure a Product

    vd_
    Watlow SELECT® Visual Designer™

    Quickly configure a product to meet the unique requirements of your application. Instantly access lead times, dimensional drawings, and more - at your own pace. No login required.

    Get Started

    Prefer to talk to a human? Find a Distributor or Sales Office 

    Part Lookup

    Know Your Part Number?

    Enter your part number exactly as marked.

    #
    Tip

    Many parts have lead times, dimensional, drawings, and more available on-demand. Click "Request a Quote" on the search result to access.

    Help Me Choose

    man with dual monitors using product selection assistant
    Not Sure? Try Our Digital Product Assistant

    Take the complexity out of product selection with our innovative Digital Product Assistant. Answer a few application questions and our interactive tool will recommend a product from our catalog.

    Launch Assistant
    Still need help? Locate a Rep Contact Us

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    icon representing a thermal loop system
    The Thermal Loop

    For Watlow, the underlying concept behind everything we do is that of the thermal loop. Every product we offer, and every project we work on, is ultimately about the creation and control of a thermal loop in an application. 

    Learn More

    Industries

    Heat Treatment Energy and Environmental Technologies Life Sciences
    Clinical Equipment Semiconductor Processing Foodservice Equipment

    Electrification

    thumbnails of white papers relating to electrification and decarbonization
    Electrification

    Over 100 years ago, Watlow began designing and manufacturing electric heating elements to replace steam in the shoe industry. We've been electrifying equipment and processes ever since. Wherever thermal is critical, no one is better equipped to help you reach your energy transition goals. Learn why leading companies partner with us.

    Learn More

    Industry 4.0

    thumbnail of industry 4.0 white paper on tablet and print
    The Thermal Loop & Industry 4.0

    Industry 4.0 technology enables the capture and processing of data in real time, both where its generated and where it is needed, to implement effective improvements to industrial processes. Capturing data, though, is not enough. The advantage Watlow® brings to an Industry 4.0 project are its thermal experts, who understand both the important role thermal loop systems play in key applications and industry 4.0 implementations.

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    Shiyi Zhou Joins Watlow® as Regional President for Asia Watlow® Welcomes Klaus Aarestrup as New Regional President of Europe Watlow’s New Large and Extra Large WATCONNECT® Control Panels Maximize Process Uptime with a Small Footprint Watlow’s New PM PLUS® 1/8 DIN PID Controller Watlow® Obtains KGS Certification on Flange and Circulation Heaters Watlow® Completes Acquisition of Eurotherm®
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StartUp
Continuous
1.  Heat to Raise          
2.  Heat to Melt          
3.  Conduction Heat Losses          
4.  Safety Factor {{SafetyFactor}}%    
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Heat to Melt

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Conduction Heat Losses

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Safety Factor

Safety factor is a subjective field to compensate for unknown heat losses or system inefficiency. Excess safety margin can drive up the overall cost of the system, while too low a value may limit system performance or cause inadequate thermal transfer. Click on Help below for specific Safety Factor recommendations.

0% 40%
{{SafetyFactor}} %
Help

Electric Heaters Power Calculations

Absorbed Energy, Heat Required to Raise the Temperature of a Material Because substances all heat differently, different amounts of heat are required in making a temperature change. The specific heat capacity of a substance is the quantity of heat needed to raise the temperature of a unit quantity of the substance by one degree. Calling the amount of heat added Q, which will cause a change in temperature ∆T to a weight of substance W, at a specific heat of material Cp, then Q =w • Cp • ∆T. Since all calculations are in watts, an additional conversion of 3.412 Btu = 1 Wh is introduced yielding:

Equation 1

QA or QB = w • Cp • ∆T

                            3.412

QA = Heat Required to Raise Temperature of Materials During Heat-Up (Wh)

QB = Heat Required to Raise Temperature of Materials Processed in Working Cycle (Wh)

w = Weight of Material (lb)

Cp = Specific Heat of Material (Btu/Ib • °F)

∆T = Temperature Rise of Material (TFinal – TInitial)(°F)

This equation should be applied to all materials absorbing heat in the application. Heated media, work being processed, vessels, racks, belts, and ventilation air should be included.

 

Example:

How much heat energy is needed to change the temperature of 50 lbs of copper from 10°F to 70°F?

Q = w • Cp • ∆T

= (50 lbs) • (0.10 Btu/Ib • °F) • (60°F) = 88 (Wh)

                                3.412
×

Electric Heaters Power Calculations

Heat Required to Melt or Vaporize a Material In considering adding heat to a substance, it is also necessary to anticipate changes in state that might occur during this heating such as melting and vaporizing. The heat needed to melt a material is known as the latent heat of fusion and represented by Hf. Another state change is involved in vaporization and condensation. The latent heat of vaporization Hv of the substance is the energy required to change a substance from a liquid to a vapor. This same amount of energy is released as the vapor condenses back to a liquid.

 

Equation 2

QC or QD = w • Hf    OR   w • Hv

                       3.412             3.412

QC = Heat Required to Melt/Vaporize Materials During Heat-Up (Wh)

QD = Heat Required to Melt/Vaporize Materials Processed in Working Cycle (Wh)

w = Weight of Material (lb)

Hf = Latent Heat of Fusion (Btu/Ib)

Hv = Latent Heat of Vaporization (Btu/lb)

Example:

How much energy is required to melt 50 lbs of lead?

Q = w • Hf 

= (50 lbs) • (9.8 Btu/Ib) = 144 (Wh)

          3.412 Btu/(Wh)

Changing state (melting and vaporizing) is a constant temperature process. The Cp value (from Equation 1) of a material also changes with a change in state. Separate calculations are thus required using Equation 1 for the material below and above the phase change temperature.

×

Conduction Heat Losses

 

Heat transfer by conduction is the contact exchange of heat from one body at a higher temperature to another body at a lower temperature, or between portions of the same body at different temperatures.

 

Equation 3A - Heat Required to Replace Conduction Losses

 

QL1 = k • A • ∆T • te

               3.412 • L

QL1= Conduction Heat Losses (Wh)

k = Thermal Conductivity (Btu • in./ft2 • °F • hour)

A = Heat Transfer Surface Area (ft2)

L = Thickness of Material (in.)

∆T = Temperature Difference Across Material (T2-T1) °F

te = Exposure Time (hr)

This expression can be used to calculate losses through insulated walls of containers or other plane surfaces where the temperature of both surfaces can be determined or estimated.

×

Safety Factor Calculation

 

Heaters should always be sized for a higher value than the calculated figure, often referred to as adding in a safety factor. Generally speaking, the fewer variables and outside influences—the smaller the safety factor.

Here are some general guidelines:

  • 10 percent safety factor for large heating systems or when there are very few unknown variables.
  • 20 percent safety factor for small to medium heating systems where you are not 100 percent sure you have accurate information.
  • 20 to 35 percent for heating systems where you are making many assumptions.
×
IMPORTANT: This Wattage Calculator is to assist you in understanding the power needs of electric thermal systems and components as they apply to various heating tasks. This Wattage Calculator is not a substitute for specific information related to complex and/or critical applications. When designing any thermal system, caution must always be exercised to comply with safety requirements, local and/or national electrical codes, agency standards, considerations for use in toxic or explosive environments and sound engineering practices. Integrity and suitability of any thermal system design/specification is ultimately the responsibility of those selecting and approving system components. If you require assistance with your calculations, please contact your local Watlow sales office or authorized distributor.
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