Btu (th)/Hour/Square Foot

The unit Btu (th)/hour/square foot measures the rate of heat transfer through a surface over time. Here, Btu (th) refers to British thermal units of thermal energy, and the measurement quantifies how much heat passes through one square foot of a material in one hour. This unit is widely used in building design, insulation analysis, and HVAC system planning to evaluate thermal performance. A higher value indicates more heat loss or gain, suggesting lower insulation efficiency, while a lower value reflects better thermal resistance. Engineers and architects rely on Btu (th)/hour/square foot to calculate heating or cooling loads, optimize energy consumption, and improve indoor comfort. It is essential for energy audits, material selection, and sustainable building practices. By accurately assessing heat transfer in this unit, professionals can design energy-efficient structures, minimize utility costs, and reduce environmental impact. Understanding Btu (th)/hour/square foot is therefore critical for both practical construction decisions and long-term energy management.

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.