Calorie (IT) per Hour per Square Centimeter [cal(IT)/(h·cm²)]

The unit calorie (IT) per hour per square centimeter, written as cal(IT)/(h·cm²), measures heat flux density or thermal power per unit area using the International Table calorie (1 cal(IT) = 4.1868 J). It represents the amount of heat energy transferred through 1 cm² of surface in 1 hour.

This unit is commonly used in solar energy studies, building physics, and small-scale thermal experiments where energy transfer over extended periods and small areas is measured. Typical applications include:

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  Solar radiation received on small surfaces

  
  
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  Thermal testing of materials over time

  
  
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  Calorimetry experiments

  
  

Mathematically, the heat flux is expressed as:

where q is heat flux in cal(IT)/(h·cm²), Q is energy in calories, A is area in cm², and t is time in hours.

Conversion to SI units:

Although SI units like W/m² are standard, cal(IT)/(h·cm²) remains useful in small-scale experiments, historical solar radiation studies, and building physics references, providing an intuitive way to quantify energy transfer per hour per unit area.

Btu (IT) per Minute per Square Foot [Btu(IT)/(min·ft²)]

The unit Btu (IT) per minute per square foot, written as Btu(IT)/(min·ft²), measures heat flux density or thermal power per unit area using the International Table British Thermal Unit (1 Btu(IT) = 1055.06 J). It represents the amount of heat energy transferred through 1 square foot of surface every minute.

This unit is commonly used in U.S. building engineering, solar energy studies, and thermal analysis where energy flux per unit area over longer periods is considered. Typical applications include:

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  Heat loss or gain through building walls, roofs, and floors

  
  
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  Solar radiation incident on panels or horizontal surfaces

  
  
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  Industrial heating or cooling rate analysis

  
  

Heat flux can be expressed mathematically as:

where q is heat flux in Btu(IT)/(min·ft²), Q is energy in Btu(IT), A is area in ft², and t is time in minutes.

Conversion to SI units:

While SI units such as W/m² are now standard, Btu(IT)/(min·ft²) remains convenient in U.S. engineering and historical thermal literature, providing an intuitive measure of heat transfer per square foot per minute.