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.

Btu (IT) per Second per Square Foot [Btu(IT)/(s·ft²)]

The unit Btu (IT) per second per square foot, written as Btu(IT)/(s·ft²), measures heat flux density or thermal power per unit area in the Imperial system 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 second.

This unit is commonly used in high-intensity heat transfer applications, solar energy studies, and engineering where energy flux per small surface area is important. Typical applications include:

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  Heat flux from industrial furnaces or heaters

  
  
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  Solar radiation incident on small surfaces

  
  
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  Thermal testing of materials

  
  

Heat flux can be expressed mathematically as:

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

Conversion to SI units:

While W/m² is the SI standard, Btu(IT)/(s·ft²) is convenient in U.S. engineering and historical references, providing an intuitive measure of high-intensity heat flux per square foot per second.