In-situ U-value Measurement of Buildings

The in-situ U-value of floors, walls and ceilings can vary significantly from calculated values. Our U-Value Measurement System is a portable tool that is used to measure the thermal transmittance of these building elements, helping to identify potential insulation upgrades and to reinforce investment decisions.

ISO 9869 U-value measurement system

ISO 9869 U-value Measurement System

U-value Measurement System including data logger, 4G modem (requires SIM card), 2 heat flux plates, 3 surface temperature sensors and 2 air temperature sensors.

What's included

  • Mains powered data logger

  • Hukseflux heat flux plates

  • Internal/external temperature sensors

  • 4G modem for remote access


£3,000 GBP
Excluding VAT & delivery

U-value measurement made accurate.

The system can record measurements over a number of days or weeks in order to deliver greater accuracy and quantify the in-situ U-value of a building envelope according to the ISO 9869 methodology.

  • Cross section of wall with insulation

    As-built performance measurement

    Conduct quality assurance testing to check that desired outcomes are being achieved. Improve quality and save costs by identifying issues early to prevent late-stage remedial work.

  • Surveyor assessing a gable wall

    Retrofit Performance Improvement

    Quantify the baseline vs the actual delivered performance. Determine the true energy, running cost and CO₂ savings delivered by improvements.

image/svg+xml ISO 9869 Certified ISO 9869 Certified
image/svg+xml UK Designed and Manufactured UK Designed and Manufactured

Improve U-value calculations

Calculating U-values using software is fraught with difficulty. Without knowing the exact construction and layer thicknesses, U-value calculations can be widely inaccurate leading to poor decision making.

All building elements

The system can measure the U-value of any external wall, floor and ceiling as long as there is a temperature difference on either side of the element.

Accurate measurements

The system can measure heat flux (Q) as well as internal & external surface and air temperatures accurately and reliably.

Unknown construction types

Using real measurements of heat flow, the system doesn't require any knowledge of the building element construction being tested.

Check quality assurance

Check that the actual performance meets the designed performance. Identify poor installations, workmanship and conduct quality assurance testing.

ISO 9869 U-value measurement

Our In-situ U-value Measurement System is a portable tool that acts as a heat flow meter and consists of a data logger, 2 x heat flux plates, surface temperature sensors, air temperature sensors, and a 4G modem all incorporated into a protective case.

The system can record heat flux measurements over a number of days or weeks in order to deliver greater accuracy and quantify the in-situ U-value of building elements according to the ISO 9869 methodology.

ISO 9869 is the recognised standard for measuring U-values that takes a minimum of 72 hours (3 days) to collect enough data to produce a valid result. More rapid U-value measurement is possible using our Heat3D infrared thermography based solution.

How are U-values measured?

In principle, the U-value can be obtained by measuring the heat flow rate through an element with a heat flow meter, together with the temperatures on both sides of the element under steady-state conditions.

Heat flow measurement

The heat flowing through the building element is measured over a number of days using heat flux plates.

Temperature readings

At the same time, the surface temperature, as well as internal & external ambient air temperatures, are recorded.

Heat flux density

The heat flux (measured in W/m²) is calculated and divided by the temperature difference (internal to external) to produce a U-value (measured in W/m²K).

U-value calculation

After a sufficient period of time (typically 7 days) and once a validity criterion has been met, an average U-value will be presented that adheres to ISO 9869 Part 1.

Frequently Asked Questions

What is a U-value?
Thermal transmittance or U-value is a measure of the rate of heat transfer through a structure. The better insulated a structure is, the lower the U-value will be and less heat loss will occur. Building regulations require new build houses and retrofit projects to achieve a certain U-value for compliance.
What is ISO 9869?
ISO 9869 is the in-situ U-value measurement standard from the International Organization for Standardization (ISO). It describes the heat flow meter method for the measurement of the thermal transmission properties of plane building components such as walls, floors and roofs.
What are heat flux plates?
A heat flux plate is a thermopile that converts thermal energy into electrical energy that can be recorded. It generates a small output voltage (in millivolts) that is proportional to the temperature differential across the plate. Logging these measurements over a long period of time allows an average heat flow rate to be calculated. We supply Hukseflux HFP-01 heat flux plates which are market leading and the world's most popular sensor for heat flux measurement.
How does the U-value measurement system work?
Our U-value measurement system uses a data logger and heat flux plates to precisely measure heat flow through building elements as well as temperature over a number of days. Using the ISO 9869 standard, we are then able to calculate an average U-value for the building element that will be much more accurate than traditional U-value calculations.