Thermal imaging vs acoustic leak detection: which finds your leak?
How thermal cameras and acoustic listening find leaks in shops and retail units, what each method is good at, where each struggles, and why engineers often use both.
If you have a leak in a shop, a stock room or a unit with a concrete floor, two words come up quickly when you speak to a leak detection company: thermal and acoustic. Both can usually find leaks without digging. They work in completely different ways, and each has conditions where it shines and conditions where it struggles.
Knowing the difference helps you read a survey quote, understand the report and prepare the site so the engineer gets a clear result.
How thermal imaging finds a leak
A thermal imaging camera measures the infrared radiation given off by a surface and turns it into a picture of temperature. The British Institute of Non-Destructive Testing (BINDT) describes the principle: the infrared radiation emitted by a structure can be measured and analysed to give information about its condition. When hot water escapes from a pipe under a floor or behind a wall, it warms the material around it. The camera shows that as a warm shape, often following the line of the pipe and spreading out where water has soaked into the screed. Heating pipes, hot water pipes and underfloor heating loops show up well for the same reason.
Cold water leaks are harder. A camera can sometimes pick out the cooler area where water sits or evaporates, but the contrast is usually weaker.
Thermal imaging works best when:
- the leaking pipe carries hot water or heating water;
- there is a clear temperature difference between the pipe and its surroundings, which may mean running the heating or hot water for a while before the survey;
- the floor or wall is visible, with stock, mats and displays moved off the suspected route.
It struggles when:
- the pipe is deep or under a thick covering, so little heat reaches the surface;
- shiny surfaces, such as polished metal or glazed tiles, reflect heat from elsewhere and muddle the picture;
- other heat sources sit nearby, such as condenser outlets, lighting, sunlight through glazing or warm air from a heater.
How acoustic leak detection finds a leak
Water escaping from a pipe under pressure makes noise. It hisses, rushes or vibrates the pipe, and that sound travels along the pipe and up through the ground or floor. Acoustic detection is the craft of listening for it.
Engineers use listening sticks on accessible fittings like stop taps and valves, ground microphones placed on the surface along the pipe route, and correlators, which take readings from sensors either side of a suspected leak and work out where the noise is coming from. Water companies use the same principle across their networks. In 2019, United Utilities said it was installing around 100,000 acoustic loggers on its underground network, each one small enough to fit in the palm of a hand.
Acoustic detection works best when:
- the pipe is under mains pressure, so the leak makes a clear noise;
- the pipe is metal, which generally carries sound further than plastic;
- the site around the listening points is reasonably quiet.
It struggles when:
- pressure is low, or the pipe is plastic, so the noise is faint or fades quickly;
- background noise is heavy: traffic, refrigeration plant, air handling units, music or trading;
- the leak is very small and makes little sound.
Side by side
| Thermal imaging | Acoustic detection | |
|---|---|---|
| What it detects | Temperature patterns on a surface | The sound of water escaping under pressure |
| Best on | Hot water, heating and underfloor heating pipes | Pressurised supply pipes and water mains, especially metal |
| Needs | A temperature difference and a clear surface | Pressure in the pipe and limited background noise |
| Main weaknesses | Deep pipes, thick coverings, reflections, other heat sources | Plastic pipe, low pressure, noisy surroundings, very small leaks |
| Disruption | Low; heating may need to run first and stock may need moving | Low; noisy work nearby may need a brief pause |
| Typical role | Showing the area and route of a hot water or heating leak | Pinpointing a supply or mains leak |
Why engineers often use both
In a real retail unit, conditions are rarely perfect for either method. Floors carry stock and fixtures, plant runs all day, and the pipe route is often a guess. So a sensible survey combines them. A thermal scan might show a warm band across the stock room floor, and acoustic listening then narrows it to a point. Or a ground microphone picks up a noise under the car park, and a second method confirms it before anyone opens the surface.
Tracer gas is the third method to know about. The suspect pipe is isolated and filled with a hydrogen and nitrogen mix, and the gas escaping at the break is picked up at the surface. It helps where thermal and acoustic both struggle: plastic pipes, low pressure and noisy sites.
Confirming a location with a second method is good practice before any floor is opened, because a hole in the wrong place costs a closed aisle and a second repair.
What to ask before you book
- Which methods will the engineer bring, and why those for your leak?
- Will the heating or hot water need to be on beforehand for a thermal survey?
- What will the report show, and will it stand up for an insurance claim?
- What happens if the leak is not found?
On that last point, our investigations are chargeable whether or not the leak is found, as set out in our terms, and the report records what was tested and ruled out.
About ADI Leak Detection
ADI has worked on leaks for over a decade, with 25 engineers across England, Scotland and Wales. We are accredited by CIPHE, WIAPS, WaterSafe and SPATA, hold £5m public liability cover, and write insurance-ready reports. We aim to find and repair on the same day wherever the job allows. You can read more on how it works, heating leak detection and underfloor leak detection.
To book a survey, call 0333 567 2615.
Frequently asked
Which method is more accurate?
Each is accurate in the right conditions. Thermal imaging suits hot water and heating pipes with a clear temperature difference; acoustic listening suits pressurised pipes in a reasonably quiet setting. A good survey often uses one method to find the area and another to confirm the exact point.
Does thermal imaging see through concrete?
It sees the surface. The camera measures infrared radiation coming off the floor or wall, so it shows where a leak has warmed or cooled the surface above it. Deep pipes, thick coverings or stock sitting on the floor can hide that pattern.
Will the survey disrupt trading?
Both methods are non-invasive. Acoustic listening can be thrown off by background noise, so the engineer may ask for a short pause in noisy work nearby, and thermal imaging works best when displays and stock are cleared off the suspected pipe route.