Thermal Imaging Basics

Start here for an introduction on how to use Thermal Imaging Cameras for finding poor insulation, draughts, central-heating faults and other building problems. Why Thermal Imaging? gives more reasons why this is worthwhile.

The same principles apply to any thermal imaging camera in taking and interpreting images
TI Cameras have differing user-interfaces – TiR and TiR105 user manuals are summarised and compared here.  Flir One instructions are online. The principles even apply to cheaper infrared thermometers – think if them as one-pixel TI ‘cameras’.

Switch-on and take a picture – people are interesting. (have you opened the lens-cap?)  Get used to which colours indicate hot and cold.  You can change this colour palette:  Iron-bow and red-blue/rainbow are the most commonly used.  Fluke’s ‘thermal fusion’ (picture-in-picture) display is good for showing the context of your thermal image, as in the lower picture.
Cold front door

Surface temperatures are shown, eg: in the cat image the 24.8°C centre-spot is the temperature of the outside of the cat’s fur. We can see thermal effects on the surface of deeper insulating or conductive features – this is what’s useful.

From inside a warm building, areas of poorer insulation, like around the window behind the cat, are shown by lower temperatures.
Whereas from outside, poorly insulated areas, like this front-door, are hotter – where more heat is escaping.
Of course this also depends on how hot the room inside is.

Don’t expect better than ±3°C accuracy – often worse. This doesn’t usually matter in building surveys, when we’re mainly making comparisons: what’s hotter or colder?

Thermal images of buildings are more vivid and revealing when the interior is at least 10°C warmer than the outside, so winter is the main survey season.  If necessary, put the heating on (or turn it up) a few hours before a survey.

Direct sun can cause confusion by heating walls, which can persist for hours afterwards. Wind and rain can cool surfaces.

See pages about Auto and Manual settings and interpreting images.  Beware of confusion caused by reflections or low-emissivity surfaces.

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