Do you need to find the position of chimney flues? Our GPR surveys provide a fast and efficient means of locating chimney flues within walls. The surveys are non-destructive and non-intrusive; therefore, we can undertake them in occupied buildings with minimum disruption.

Flue location surveys

GPR detects changes in the sub-surface. In the case of flues, the flue void is detected due to the drastic change in material properties of the masonry wall and the flue void.

Our chimney flue location surveys are carried out by Sandberg-trained, experienced GPR surveyors. We scan nominated walls with horizontal scan lines at regular intervals. The spacing depends on site conditions, but typically, we scan at 300 mm centres.

Surveyor using Ground Penetrating Radar to scan walls and locate chimney flues
Chimney flue location survey

In most cases, we use a GSSI SIR3000/4000 GPR control unit with a 1500/1600 MHz antenna. We can use lower frequencies on thick walls to provide greater penetration depth, but the resolution and detail of GPR scan data decrease with lower antenna frequencies. Therefore, it is desirable to use the highest frequency possible while still meeting the objectives of the survey.

GPR works on most materials; however, the signal does not travel well across voids. Therefore, it does not work on panelling, dry lining, or stud wall construction. Irregular surfaces, such as ornate mouldings, may result in poor surface coupling and antenna tracking problems, which can affect the positional accuracy of detected flues.


We present our interpretation results in a comprehensive factual report in PDF format. The report includes CAD elevation drawings marked with the location of all detected flues. We also issue the original CAD drawings in AutoCAD .dwg format.

Chimney flue CAD plot
Detected chimney flue locations plotted in CAD (click image for larger version)

Advantages of a GPR chimney flue survey

We can interpret the GPR data on-site in real time to provide instant results with an on-site markup. However, we recommend off-site data processing and analysis, which produces better and more accurate results. Typically, we save the GPR data electronically for off-site analysis. The position of detected flues is plotted on CAD elevation drawings.

Advantages of our GPR chimney flue surveys:

  • Non-intrusive
  • No damage to the building’s structure
  • No noise or dangerous emissions
  • Suitable for occupied buildings
  • Minimum disruption to the occupants
  • No need to remove decorative finishes
  • Quick and efficient
  • Flue paths plotted in CAD
  • Flues marked up in situ if required

Why locate chimney flues?

It is often necessary to accurately locate the position of chimney flues before opening up walls. This can be for access, connecting adjoining properties, or reusing redundant flue voids as ventilation or service ducts. In building refurbishment works, it is also frequently necessary to locate flues, or more specifically, areas of solid masonry away from flues, to support structural steel beams. A GPR flue location survey can provide essential information during preliminary feasibility studies or the planning stage. GPR makes this possible with no damage to the building fabric or decorative finishes.

Definition of a chimney flue

A chimney flue is a near-vertical structure made of masonry, clay or metal. Its purpose is to contain and transfer smoke and gasses from a fire or boiler to the outside. Find out more about chimney flues on Wikipedia.

Need more information?

Contact us

Contact us to find out more about GPR chimney flue location surveys and how we can help you:

Tel: 0207 565 7056

Information sheet

Download our information sheet about GPR chimney flue location surveys.

Are you wondering what else GPR can be used for? GPR surveys can investigate the subsurface and detect unseen features. Learn more about our most popular GPR surveys.