U-value is the term used to describe the heat transfer coefficient of a building element (e.g. of a wall). The U-value describes the insulation quality of a building. The unit of the U-value is W/(m²K). The lower a U-value, the better the insulation quality of the building element.

U-Value Measurements

But how to measure the U-value? Our measurement-approach uses a heat flux sensor and two temperature sensors (see image below). This approach is standardized in ISO 9869, ASTM C1046 and ASTM C1155. This is the only method which delivers reliable quantitative in-situ information about a building envelope.

Read about a U-Value measurement with our gSKIN® U-Value KIT in a case study from ETH Zurich.

In a study sponsored by the Swiss Federal Office of Energy and conducted by Hässig Sustech, the gSKIN® U-Value Kit was used to measure the insulation quality of walls in older buildings. The English abstract is available on page 3 of the study which can be accessed here.

We also offer a cloud-based, wireless solution for U-value, R-value, temperature, and humidity measurements. More information is available here.

greenTEGs U-value measurement device gSKIN U-Value Kit

To differentiate our measurement-approach from other often applied approaches we reviewed the most common ones:

  1. Table Look-up (Building Catalogue)/ U-Value Calculation
    There are complex databases containing λ-Values of generic building elements ordered by element material and/or year of construction. With these databases, the U-value of a building envelope (e.g. wall) is calculated by adding all materials contained within the specific element (e.g. specific wall = 20cm concrete + 20cm glass wool). While this method is very simple and quick, it does not produce an accurate U-Value, only an approximation.

  2. Thermography (i.e. Infrared imaging)
    This approach shows the thermal radiation of an object and produces an image showing spots with higher and lower radiation. An infrared image gives only qualitative results, hence an U-value cannot be determined. 

  3. Multiple Temperature Measurement
    This approach is based on three or more temperature measurements on both inside and outside of a building element. While this approach produces a U-Value, it needs a minimum temperature difference of 10 °C between the inside and outside to work and it is assumend that the thermal boundary resistance is constant.

U-Value Measurements with greenTEG's Kit: fast & easy

Easy to mount

You can use normal adhesive tape to fix our sensor to any wall or window.

Easy to transport

The U-value Kit can easily be carried in our transportation box.

Real-time review

You can review measurement protocols easily on your laptop.

Short measurement

If you do not need to follow ISO guidelines, you can measure U-Values in less than an hour.

Easy analysis

A professional, easily understood software is provided

Many applications

The U-Value Kit / Sensors can be applied within R&D applications to e.g. improve insulation of materials, etc.


Typical application areas include measurement of building insulation, windows, and various industry driven R&D fields.

Thermal energy enters buildings mainly from the heating system and from solar irradiation. The energy exchange between the building and the outside is focused through the roof, walls, windows, and thermal bridges e.g. balconies, into the soil, and through exchange of ambient air. Every building is a complex thermal system and to optimize these systems (for example to reduce heating costs), precise data is required. Download the Building Physics Application Note.

As the measurement set up for glass differs due its low thermal capacity to the influence of radiation for opaque materials. Our U-Value-Kit can also be easily used to measure the U-Value of windows. Learn more in our application note.

How to measure the U-value? 6 Steps to get started

Choose an optimal measurement spot on the building element of interest.

On the inside of this spot, place the heat flux sensor, and one temperature sensor.

On the outside of this spot, place the second temperature sensor.

Connect all three sensors to the data logging unit.

Start the measurement process (via your Laptop).

Evaluate the U-value of the wall element with the software included .

Buy the U Value Kit, Heat-Flux Sensors and our other products online

Detailed information about the U-Value Kit is available in our online shop.





Overview of the key features


Instruction manual

R-value vs. U-value

Comparison: Heat flux vs. temperature method

Summary of ISO 9869


U-value measurement saves cash

Measurement vs. calculation

Chinese – U值测定 节能之道

French – Coefficient de transmission thermique

Greek - Αξιολόγηση U-Value - αξιοποίηση χρημάτων

Japanese – “U値”評価 = 数値として評価を得る

Korean – U-Value 측정 솔루션

Russian – U-value

Spanish – Determinación del Valor-U – L calidad-precio

Swedish – U-värdesmätning – valuta för pengarna!

Bahasa U-Value


Building physics

Minergie verification measurements (by ETH Zurich)



Occupied building

Quarrystone wall



greenTEG develops, manufactures, and markets thermal sensor solutions. The company was founded in 2009 as an ETH Zurich spin-off and has since built up an international customer base, coupled with a global distributor network.

greenTEG’s thermal sensors are integrated into diverse applications by customers active in markets such as laser, building technologies, medtech, automotive, processing industry, and R&D.

Contact us or our distributors and tell us about your application ideas. We will support you to find the best solution for your requirements.More information about the company and its technology can be found on their website.

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Our partnerships and recognition

The Swiss Federal Office of Energy supported us with its expertise during the development of our technology. In 2010, greenTEG got certified by the Commission for Technology and Innovation (CTI). Together with our partner Climate KIC we exhibit our technology at the Umweltarena Spreitenbach.