HDElectHeat application icon HDElectHeat Electric Duct Heater Calculator

HDElectHeat is a precise desktop tool for sizing and verifying electric duct heaters used in HVAC air-handling and terminal-unit applications. Whether you are selecting a heater for a new system, confirming that an existing unit meets code-required watt-density limits, or checking current draw for panel coordination, HDElectHeat delivers the complete set of electric-heat performance results in seconds.

HDElectHeat handles both common element types and both standard power configurations:

  • Open-Coil Elements — bare-wire nichrome resistance elements suspended in the airstream; higher maximum watt density (up to 28.9 kW/sq.ft.) for general duct-heat applications.
  • Finned-Tube Elements — resistance wire inside a sheathed, finned tube; lower maximum watt density (up to 17 kW/sq.ft.) with improved element protection, suitable for lower-velocity or higher-temperature applications.
  • Single-Phase and Three-Phase — current draw is computed for either configuration from the entered voltage and calculated heater size.

Specify the duct airflow, heater face dimensions, and either the desired leaving-air temperature or the heater size in kilowatts, and HDElectHeat instantly computes the full performance picture, flags any watt-density violations, and reports the absolute maximum heater capacity the duct geometry and airflow will support.

KEY FEATURES

  1. Computes Temperature Rise and Leaving Air Temperature from airflow and heater kW, or solves for kW from a target leaving temperature.
  2. Calculates Sensible Heat Output in Btu/hr (IP) or kW (SI) using the standard sensible-heat equation for air.
  3. Calculates Current Draw (Amps) for single-phase or three-phase power supply at the specified voltage.
  4. Calculates Air Pressure Drop across the element bank (in. W.C. or Pa) as a function of element-face velocity, for both open-coil and finned-tube element types.
  5. Computes Watt Density (kW/sq.ft. or kW/sq.m) and compares it against the NEC- and manufacturer-recommended maximum for the selected element type, with a clear pass/fail indication.
  6. Computes Heater Face Area and Element Face Area (subtracting frame allowances) from the entered height and width dimensions.
  7. Computes Element Face Velocity and the Minimum Required Element Velocity for the entered watt density and entering-air temperature, so airflow adequacy can be verified in a single glance.
  8. Reports Maximum Allowable Heater Size (kW) and the corresponding Maximum Leaving Air Temperature for the duct geometry and airflow, giving the designer the full operating envelope.
  9. Full IP and SI unit support — toggle between °F/cfm/in. and °C/l s/cm with a single click; all inputs and results convert automatically.
  10. PDF report generation — produces a cleanly formatted summary of all inputs and results, ready to attach to any project submittal or equipment schedule.
  11. Clipboard copy — exports all inputs and results as tab-delimited text for pasting directly into spreadsheets or project reports.
HDElectHeat inputs and electric heater results screenshot

INPUTS

HDElectHeat accepts the following parameters to fully define the electric heater selection:

  • Airflow — volumetric flow rate through the heater (cfm or l/s)
  • Heater Height — overall face height of the heater casing (in. or cm)
  • Heater Width — overall face width of the heater casing (in. or cm); the element face area is computed by subtracting standard frame allowances from both dimensions
  • Entering Air Temperature — dry-bulb temperature of the air entering the heater (°F or °C); determines the velocity-limited watt-density curve
  • Leaving Air Temperature — target supply-air temperature leaving the heater (°F or °C); enter this or Heater Size, not both
  • Heater Size (kW) — installed heater capacity in kilowatts; enter this or Leaving Air Temperature, not both; kW is the same in IP and SI
  • Element Type — Open Coil or Finned Tube; controls the watt-density limit and pressure-drop equation used
  • Phase — Single Phase or Three Phase; used to compute current draw from voltage and kW
  • Voltage — supply voltage (V); common values are 120, 208, 240, 277, 460, or 480 V

RESULTS COMPUTED

HDElectHeat reports the following outputs after each calculation:

  • Heater Size — calculated or confirmed heater capacity (kW)
  • Temperature Rise — dry-bulb temperature increase across the heater (°F or °C)
  • Leaving Air Temperature — calculated or confirmed supply-air temperature (°F or °C)
  • Sensible Energy — total heat delivered to the airstream (Btu/hr or kW)
  • Static Pressure Drop — resistance of the element bank to airflow (in. W.C. or Pa)
  • Current Draw — full-load amperage at the specified voltage and phase (A)
  • Watt Density — heater output per unit of element face area (kW/sq.ft. or kW/sq.m); compared against the recommended maximum for the element type
  • Heater Face Area — overall face area from the entered dimensions (sq.ft. or sq.m)
  • Element Face Area — net element area after subtracting frame allowances (sq.ft. or sq.m)
  • Element Face Velocity — actual air velocity through the element face (ft/min or m/s)
  • Minimum Element Velocity — lowest velocity required to keep watt density within the safe limit at the computed kW/sq.ft. (ft/min or m/s); element velocity must exceed this value
  • Maximum Watt Density — recommended upper limit for the selected element type (kW/sq.ft. or kW/sq.m)
  • Maximum Heater Size — largest heater that can be installed in the given duct at the given airflow without exceeding the watt-density limit (kW)
  • Maximum Leaving Temperature — supply-air temperature corresponding to the maximum heater size (°F or °C)
View more app screenshots here.

System Requirements

  • Windows 10 or Windows 11
  • .NET 8 Runtime (included in installer)
  • 50 MB disk space

About Hands Down Software