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What is the U-value?

A great deal of energy is wasted by heating and cooling buildings that (now) fail to meet the relevant standards. The U-value provides an insight into the heat loss. The lower the U-value of a measured component, the lower the heat loss and, therefore, the better the insulation performance.

greenteg’s uval gt Wireless Kit
greenteg’s uval gt Wireless Kit
greenteg’s uval gt Wireless Kit


The heat transfer coefficient, or U-value for short, measures the heat permeability of surfaces. It is calculated as the volume of thermal energy flowing through a surface. The U-value is expressed in units of W/m2K or simply W and is calculated using the heat flux (in watts = W) flowing through one square meter of exterior wall or window when it is one degree (in Kelvin = K, corresponds to one degree Celsius) colder outside that inside.

The heat flux is therefore caused by the temperature differences in a given system. Heat always flows from the warmer side to the cooler side and can pass through solids, gases, fluids and electromagnetic waves. Heat radiation and convection (thermal conductivity) at the surfaces play a key role.

The U-value therefore determines the thermal conductivity and thickness of a material and provides insight into the thermal insulation capability of structural elements such as walls, doors and windows. The lower the value, the less heat is lost through the measured component. Therefore, the lower the U-value, the better because less heat is conducted and lost.


uvalgt Building sensor technology allows for straightforward and precise measurement of the U-value of building envelopes, structural elements, and materials.

The uvalgt wireless kit data measuring device is used to conduct simultaneous measurements of the U-value and the ambient and surface temperatures (indoors and outdoors) at five sensor points, with the option of cloud-based data transmission, analysis and monitoring in real time.


  • Straightforward, standard-conforming measurement of the U-value
  • Real-time measurement directly on a laptop
  • Simple, calibrated plug & play solution
  • Analyses and performance logs via user-friendly software
  • CSV export feature
  • ISO 9869 certified, ASTM C1046 and ASTM C1155 standardized
  • Patented Swiss measurement technology
  • Compact transport case
  • Versatile equipment for a wide variety of applications

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