Breakthrough in measuring thermal performance of buildings

Accurately assessing the thermal performance of buildings has long posed a challenge for surveyors, architects, and energy consultants. Traditionally, calculating a building’s U-value—the measure of how effectively a wall, roof, or floor resists heat transfer—required the laborious and costly use of heat-flux plates and data loggers. This process often took a week or more, involved intrusive installation, and only produced results for isolated points of a structure.

Now, a new solution is emerging that offers surveyors a faster, more precise, and far more cost-effective approach. At the heart of this breakthrough is the FLIR ONE Pro thermal imaging camera, integrated within the innovative Heat3D® system developed by Build Test Solutions (BTS). The technology has already been deployed at historic landmarks such as Westminster Abbey, demonstrating its potential to transform both heritage conservation and new-build energy efficiency.

The Limitations of traditional heat-flux plate testing

The conventional approach to U-value measurement comes with several challenges:

Time-consuming: Sensors must remain attached to walls for 3–7 days, depending on the building’s thermal mass.
Intrusive: Installation involves fixing probes and monitoring equipment to internal walls.
Costly: Multiple site visits are required, increasing survey expenses.
Limited accuracy: Heat-flux plates only capture measurements from a small, single point—often leading to misleading results if placed on a mortar joint or wall tie.

Given these drawbacks, the need for a faster, scalable solution has been pressing, particularly in the context of the UK’s net zero goals and the rising importance of accurate energy modelling in both retrofit and new-build projects.

Heat3D: a step-change in measuring building U-values

Co-developed by Build Test Solutions (BTS), Heat3D® leverages the power of infrared thermography to provide whole-wall U-value measurements in line with ISO 9869-2 standards.

Unlike traditional methods, Heat3D combines:

A FLIR ONE Pro thermal imaging camera attached to an iOS device
Bespoke calibration targets for highly accurate temperature readings
A proprietary app that generates a 3D heat transfer map

This setup allows surveyors to complete in-situ U-value measurements in just one hour, with results covering the full surface of a wall rather than isolated points.

Key benefits include:

Rapid setup: Surveys can begin within 15 minutes.
Faster results: U-value data is available in just one hour.
Greater accuracy: Whole-wall assessment reduces the risk of unrepresentative measurements.
Lower costs: Typically half the cost of a traditional heat-flux plate survey.
Cloud-enabled: All data is stored securely for analysis and reporting.

Westminster Abbey: a case study in thermal assessment

One of the most high-profile applications of Heat3D so far has been at Westminster Abbey, where energy-efficiency upgrades are underway across a diverse estate of historic buildings.

The challenge

The Grade I listed Deanery, parts of which date back to the 13th century, was identified as having particularly high energy consumption. Its thick masonry, timber panelling, and metal-framed windows posed significant challenges for improving energy performance without compromising heritage features.

The solution

Consultants Keegans deployed the Heat3D system to measure the U-values of both brick and stone walls.

The results

Predicted U-value of brick walls: 1.7 W/m²K
Measured U-value: 0.8 W/m²K (53% better than assumed)
Predicted U-value of stone walls: 2.0 W/m²K
Measured U-value: 0.9 W/m²K (55% better than assumed)

These more accurate figures provided the Abbey with confidence to pursue cost-effective, targeted interventions such as secondary glazing and improved heating controls, rather than disruptive and expensive internal insulation. The refined energy model also delivered a 16% improvement in forecasting accuracy, equating to more than £1,000 in annual savings for just one building.

How Heat3D works in practice

The Heat3D system combines hardware, software, and infrared imaging to deliver repeatable and validated U-value measurements.

Setup: An iPhone or iPad is mounted on a tripod with the FLIR ONE Pro camera attached.
Calibration: Two targets—a black body reference and a radiative reflector—are placed against the wall for precise temperature calibration.
Data capture: The camera records an infrared image every minute for one hour.
Analysis: The app calculates heat transfer across the full wall surface, identifying U-values, thermal bridges, and potential defects.
Reporting: Results are securely uploaded to the BTS cloud platform for analysis and storage.

This non-invasive thermal performance testing is already validated against more than 500 heat-flux plate comparisons, with development supported by partners such as the National Physical Laboratory and Salford University’s Energy House facility.

Applications beyond heritage properties

While Westminster Abbey provides a compelling heritage case study, the potential for Heat3D extends across the built environment:

Retrofit projects: Supporting accurate energy modelling for housing upgrades.
New-build developments: Validating whether homes meet design-stage performance specifications.
Facilities management: Identifying thermal bridges and improving operational efficiency.
Sustainability strategies: Enabling data-driven investment in energy efficiency to support net zero targets.

A new era for building thermal performance measurement

The FLIR ONE Pro-powered Heat3D system represents a step-change in how building surveyors, consultants, and property owners assess thermal performance. By making U-value measurement faster, more reliable, and more affordable, this technology helps unlock better energy modelling, smarter retrofit decisions, and improved sustainability outcomes.

From historic landmarks like Westminster Abbey to modern housing developments, the benefits are clear: more accurate data, reduced costs, and the confidence to make informed investment decisions without unnecessary disruption.

As the built environment sector accelerates towards net zero carbon goals, innovations like Heat3D—built on the reliability of FLIR thermal imaging technology—are set to play a vital role in delivering energy-efficient, resilient, and future-ready buildings.

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