Temperature Drop Calculator for Air in Ducts

    This calculator estimates the temperature drop (or rise) of air flowing in a duct.

    An example is the use of insulation to minimize temperature change (either temperature drop or rise) of a supply duct in a commercial building.

    Temperature Drop Calculator for Air Ducts
    ASHRAE 2009 HoF, Chapter 4, Equation 48 (page 4.21)


    Users will need to input the following:

    • Entering air temperature in °F
    • Ambient temperature in °F
    • Flow rate of air in cubic feet per minute (cfm)
    • Length of duct run in feet
    • Perimeter of duct in inches
    • R value of duct insulation (interior liner or exterior duct wrap)


    Based on input, calculator will provide the following:

    • Temperature drop in °F Leaving air temperature in °F

    Release Notes

    The calculators are housed at the National Institute of Building Sciences' Whole Building Design Guide (WBDG) website under the Mechanical Insulation Design Guide (MIDG). Calculators can be used online without any specific software requirement, and you can print the results page for each calculation.

    For More Information

    For more information, use the comment page or contact the National Insulation Association help desk at niainfo@insulation.org or 703-464-6422.

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