Combined Blower Door Thermal Imaging Surveys

It not common knowledge but one of the best surveys you can undertake to any new, or existing building (about to be retrofitted) is a combined blower door & thermal imaging survey. A blower door/thermal imaging survey is undertaken installing a large Retrotec fan within a fabric-covered frame to induce a negative pressure within a building. Introducing negative pressure (approximately minus 20Pa) to a building exaggerates thermal anomalies, such as air infiltration, which may not be clear under normal operating conditions. Air leakage paths can be quickly identified and detailed reports produced recording the defects, so remedial works can be accurately targeted.

Attaining extra BREEAM credits via Air Testing and Thermal Imaging 

The depressurising kit is known as a blower door system and is more commonly used to measure the air tightness/permeability of new dwellings and commercial buildings. Air tightness testing is one of a series of compliance tests that are required under Building Regulations Part L. For a thermal imaging application, many companies are not interested in the actual air leakage result, they simply use the equipment, to provide a controlled way to depressurise the building; however, as BREEAM provides extra points for undertaking air tightness testing to retrofit projects etc. we also provide a UKAS complaint air tightness test reports for each project.


How we conduct depressurised Thermal Image Surveys

A typical blower door-assisted thermal imaging survey of the interior of a building, or single room, would be conducted in the following way:

  1. Ensure you have a good quality thermal imaging camera with the minimum resolution required for BREEAM. Also, a high-powered fan system that can pressurise the building to a minimum of 8m3/hr/m2 at 50Pa.
  2. Confirm acceptable environmental conditions for a thermographic survey are in line with Annex D of BS 13187.
  3. Carry out temporary sealing of mechanical ventilation etc. as required by ATTMA and Building Regulations Part L.
  4. Set up the blower door in the opening of an external door.
  5. Set up the fan to depressurise the building at minus 20-30Pa for approx. 10 mins. This will accentuate the temperature difference across the building envelope.
  6. Maintain this pressure and walk around the building identifying areas of intertest.
  7. Continue to depressurise the buildings in steps of 10pa increments and inspect at each pressure i.e.: -20 / – 30 / – 40 / – 50Pa. Ensure that there is a clear record of which images were taken at which pressure.


The main benefits of combined Thermal and Blower Door Testing

The principal benefit of this combined testing method is that you can see thermal defects (such as air leakage paths) much more easily due to the increased building pressure. In the case of air infiltration where the thermal pattern commonly appears as fingers or branches at lower temperatures around the plasterboard, these patterns will become easier to see. As the negative pressure increases, more air will try to force its way in from outside. It’s worth noting that 50 Pa is the equivalent of a 20-mph wind blowing against all sides of the building envelope simultaneously, which is quite common in the UK. The blower door acts as an amplifier for the thermal imaging camera which helps to supercharge the results.

Only use highly trained test engineers 

Please be aware of our high specification utilised in these inspections which surpasses those required by BREEAM, our Air tightness testers are UKAS and ATTMA accredited, and our thermographers are Level 3 certified, which is the highest accreditation available.

It’ worth noting that our air tightness and thermal imaging services include the following:

  • UKAS accredited company
  • ATTMA Level 2 certified
  • The most powerful modular blower door systems
  • UKAS calibrated equipment
  • Level 3 thermographic certification
  • Large format FLIR cameras with 45-degree lenses
  • A detailed report which includes thermal indexing formula for fault diagnosis, qualification, and severity grading.

We provide combined Thermal Imaging and Blower Door Testing

If you would like a combined blower door and thermal imaging survey please contact Darren on 07775623464 or email us at For more information on how to prepare your building for the thermal survey please download our thermal imaging checklist.

We are a UKAS and ATTMA accredited company for air tightness testing and our Thermal Imaging Engineers are trained to Level 3.