Electric Duct Heater Sizing Calculator

Heater Size Formula:

\[ \text{Size (kW)} = \frac{\text{Airflow (cfm)} \times \Delta T (\text{°F}) \times \text{Factor (BTU/cfm °F)}}{3412} \]

Heater Size:

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1. What is an Electric Duct Heater Sizing Calculator?

Definition: This calculator determines the required kilowatt (kW) capacity of an electric duct heater based on airflow, desired temperature rise, and conversion factors.

Purpose: It helps HVAC professionals and engineers properly size electric duct heaters for air handling systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{Size (kW)} = \frac{\text{Airflow (cfm)} \times \Delta T (\text{°F}) \times \text{Factor (BTU/cfm °F)}}{3412} \]

Where:

Size — Required heater capacity in kilowatts (kW)
Airflow — Air volume in cubic feet per minute (cfm)
ΔT — Desired temperature rise in degrees Fahrenheit (°F)
Factor — Conversion factor (1.08 BTU/cfm °F for standard air)
3412 — Conversion from BTU/hr to kW (1 kW = 3412 BTU/hr)

Explanation: The formula calculates the heat energy needed to raise the temperature of the airflow by the specified amount.

3. Importance of Proper Heater Sizing

Details: Correct sizing ensures efficient operation, prevents energy waste, and maintains system safety. Oversized heaters cycle too frequently, while undersized ones can't maintain desired temperatures.

4. Using the Calculator

Tips: Enter the airflow in cfm, desired temperature rise in °F, and conversion factor (default 1.08 BTU/cfm °F for standard air). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the standard conversion factor (1.08) based on?
A: It's derived from the specific heat of air (0.24 BTU/lb °F) and standard air density (0.075 lb/ft³), multiplied by 60 minutes/hour.

Q2: When would I change the conversion factor?
A: Adjust for high altitude (lower air density) or special gas mixtures. At 5000 ft, use approximately 0.95 instead of 1.08.

Q3: What's a typical temperature rise for HVAC systems?
A: Common ΔT values range from 20-50°F for comfort heating, but can be higher for industrial processes.

Q4: How do I determine the required airflow?
A: Calculate based on room volume and desired air changes per hour, or use CFM = (BTU/hr)/(1.08 × ΔT).

Q5: Does this include safety factors?
A: No, consider adding 10-20% to the calculated size for safety margin and voltage fluctuations.