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.

Erg per Hour per Square Millimeter [erg/(h·mm²)]

The unit erg per hour per square millimeter, written as erg/(h·mm²), measures energy flux density or power per unit area using the cgs system. An erg is defined as the energy required to move 1 dyne over 1 centimeter, or 1 erg = 10⁻⁷ joules. Dividing by hour and mm² provides the rate of energy transfer per small area over time.

This unit is typically used in laboratory-scale physics, radiation experiments, and surface energy studies where small areas and low energy transfers are involved. Applications include:

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  Measuring radiation incident on tiny surfaces

  
  
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  Calorimetry experiments on small samples

  
  
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  Micro-scale energy transfer studies in materials science

  
  

Heat or energy flux can be expressed mathematically as:

where q is energy flux in erg/(h·mm²), E is energy in ergs, A is area in mm², and t is time in hours.

Conversion to SI units:

While largely of historical or specialized use, erg/(h·mm²) provides a convenient cgs-based measure for micro-scale, low-intensity energy transfer in scientific experiments.