How Thermal Cameras Find Leaks Without Opening Walls

Thermal camera leak detection works by showing small temperature differences on the surface of a wall, ceiling or floor. Wet material is usually a little cooler than dry material beside it because water evaporating from it carries heat away, so damp areas show up as distinct shapes on the screen. The camera does not see through the wall or see water itself, which is why every suspect area is then confirmed with a moisture meter.

How thermal camera leak detection works

Everything gives off infrared energy according to its temperature. A thermal camera reads that energy and turns it into a picture where each colour stands for a surface temperature. On a dry interior wall the picture is fairly even, with faint lines where the studs are.

Add water and the picture changes. Damp drywall cools as moisture evaporates from it, so it shows as a darker, cooler patch. Wet material also holds heat differently from dry material, so when the room warms up or cools down the wet area lags behind and stands out. A leaking hot water line does the opposite and shows as a warm streak. The shape matters as much as the colour. Water running down inside a wall leaves a cool pattern that is narrow at the top and spreads toward the floor. Water spreading across a ceiling leaves an irregular blob, often with a tail leading back toward the source.

What a thermal camera can and cannot see

It reads surfaces only. It cannot look into a cavity and show a pipe with a drip on it. What it shows is the effect of that drip on the back of the drywall once enough moisture has reached it.

It also cannot tell water from anything else that changes surface temperature. All of these look cool on a scan and none of them are leaks:

• A stud bay with missing or slumped insulation on an exterior wall.
• Cold air leaking in around a window, an outlet box or a rim joist.
• A supply duct or cold water pipe running behind the surface.

Shiny surfaces cause a different problem. Glazed tile, mirrors, stainless steel and polished stone reflect infrared like a mirror reflects light, so the camera picks up the reflection of the room or the person holding it. Readings on those surfaces need extra care and usually a second method.

Why a moisture meter always follows the camera

The camera is the fast way to find where to look. The moisture meter is how you know. A pinless meter is pressed flat against the surface and senses moisture a short distance into the material without leaving a mark. A pin meter pushes two small probes into the material and gives a direct reading, which for wood framing is a percent moisture content.

A proper inspection uses both tools together. The camera sweeps the room and flags the cool patterns. The meter checks each one and also checks a dry area of the same material for comparison. A cool patch that reads dry on the meter is an insulation or air leak issue. A cool patch that reads wet is mapped out and photographed.

What conditions give a reliable scan?

Thermal imaging needs a temperature difference to work with. For moisture inside the house, that mostly comes from evaporation, so a wall that is actively wet shows well. A spot that got wet weeks ago and has reached the same temperature as everything around it may show faintly or not at all, even though the meter still reads high.

A few things improve the result:

• For plumbing leaks, running the suspect fixture before and during the scan. Running hot water makes supply leaks stand out clearly.
• For exterior walls and ceilings, a real difference between indoor and outdoor temperature. A cold January day or a hot July afternoon in London both work. A mild day with the windows open works poorly.
• Steady indoor conditions. A wall in direct sun or beside a hot register is hard to read.

Which leaks it finds well and which it misses

The camera is strong on ceiling leaks under bathrooms and roofs, supply line leaks in walls, wet insulation, water tracking under flooring from a dishwasher or fridge line, and the spread of water after a burst or overflow. It is also the quickest way to see how far water travelled past the visible stain, which is usually farther than people expect.

It is weaker on leaks behind thick tile and stone, very slow leaks that have not yet wetted the surface layer, water under a concrete slab, and anything behind cabinets or built-ins that block the view. In those cases the meter, a small inspection opening or a plumber's pressure test fills in the gap.

Getting ready for a thermal inspection

Pull furniture a metre back from the suspect walls, keep the house at its normal temperature for a few hours beforehand, and write down when the problem shows up: after showers, after rain, or all the time. Avoid running fans or heaters at the wet spot that morning, since drying the surface hides the pattern. Our leak detection and moisture inspections run $249 to $549 and include the thermal images and the meter readings side by side.

Common questions