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 (th) per Second per Square Centimeter [cal(th)/(s·cm²)]

The unit calorie (th) per second per square centimeter, written as cal(th)/(s·cm²), measures heat flux density or power per unit area using the thermochemical calorie (1 cal(th) = 4.184 J). It represents the amount of heat energy transferred through 1 cm² of surface every second.

This unit is commonly used in laboratory-scale heat transfer experiments, solar energy studies, and focused radiation applications, especially where the energy is concentrated over a small surface area. Applications include:

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  Solar radiation intensity measurements

  
  
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  Laser or concentrated light experiments

  
  
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  Calorimetry experiments on small samples

  
  

Heat flux can be expressed mathematically as:

where q is heat flux in cal(th)/(s·cm²), Q is energy in calories, A is area in cm², and t is time in seconds.

Conversion to SI units:

While W/m² is the SI standard, cal(th)/(s·cm²) remains useful in laboratory and historical references, providing a practical measure for high-intensity, small-area heat transfer.