What Does This Heat Photo Show?

This FLIR camera photo shows a blue strip along the edge of a ceiling, apparently 18deg; the adjacent ceiling and walls are yellow/orange, apparently 12deg. I had thought the blue strip indicated a cold spot - but the temp scale says it’s warmer, albeit depicted blue. Explanations gratefully received!


Can you describe the location and where you were relative to it? Maybe a photo in the optical spectrum of the same location.

Apparent anomalies are often not what they first seem.

Is this the same location that we discussed in another thread?

Hello again Tim - yes it is indeed the same; the photo is looking up, the curved/45deg-angle section is showing blue, then the rest of the ceiling that is above/adjacent is yellow/orange, and the wall below is yellow/orange. (I have other heat photos showing the same in other rooms and areas upstairs.)

I don’t suppose you have external images showing each side of the roof line?
It would be nice to see but air movement over the top of the ceiling/slope insulation will obscure the results.

Do you know what the ceiling, wall and slope insulation types and thicknesses are?
Is any of the insulation and/or any insulated surfaces foil faced?
Is there any overlap or abutment between insulation areas/types?

Unfortunately I didn’t take outside photos of the roof. (Will do, another time.) But as you say, air movement must make that hard to interpret.
Ceiling insulated by about 250mm of rockwool, in the loft.
Wall insulation is blown-in EPS (recent), so 50mm or so thick I think.
The slope has had insulation blocks fitted (also recent, by temporarily raising two courses of tiles), not v thick, 25mm- 50mm from memory. Not sure about foil.
Not detailed abutment/overlap - tho I think the slope-blocks did reach to the edges of the ‘overhead’ layer of rockwool. More or less.

There is nothing in your description that fits in with the key to temperatures. Your description explains well the image without the key, always assuming that blue is cold and red is hot (like on a tap). I am unable to explain the phenomenon. I hope that someone else can help with this, and I have @Frank_Reif in mind. From previous posts on other threads our knowledge seems to complement each other.

Well, it’s not from internal heat sources, otherwise the better insulated surfaces would be warmer. That leaves the sun. Was it sunny, is it on the south face?

My guess is that solar gain on the tiles, and warm air venting up from the external walls into the sofitts under the eves.

Radiative coupling from the tiles and convection/wind washing, through the insulation may be the cause.

The scales do seem counter intuitive. It could also be a problem with the settings and the file export.

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Thank you @Frank_Reif. Yes, I forgot to ask about the weather when the photos were taken. Wind washing is very hungry for household heat and nearly always not catered for.



Thanks both. It was 3am, in early February. I had previously been assuming blue= cold, yellow/orange= warm; the photos accord with that - but the scale is a complete mystery, which I hadn’t really noticed before.

As Frank implied and I had been contemplating, it seems as though the camera needs a service and re-calibrating.

Is this a Carbon Co-op Flir camera? If so I think @mattfranklin needs to be advised. The UK thermal image season is ending and the camera should be available for servicing. Meanwhile anyone else using it should probably be sent a caveat.

Yes it’s a C/Co-op camera, I’ll let Matt know.
An improvisation this morning with an electronic thermometer Blutak’d to the relevant surfaces suggests a similar cold-ish strip along the curved section of ceiling - albeit only a degree or two, but that might be because the heating’s only on for 2hrs in the morning. I’ll look again at 10pm, when heating will have been on for 5hrs.
Adobe Scan 09 Mar 2023_temp_diff1.pdf (120.1 KB)
Adobe Scan 09 Mar 2023_temp_diff2.pdf (430.7 KB)
(Can you actually open those Pdf’s? - seems to link back to a folder on my laptop.)

Yes, I can see your inside/outside thermometer being put to novel use.

The actual temperatures will be slightly out due to picking up room temperature too but you are only looking for a guideline. Very innovative.

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Think I’ll just go ahead with your PIR-board ‘recipe’, on 1 or 2 of the offending surfaces - then check again next winter! I’ve advised Matt of the apparent scales-display problem.

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I suggest starting with the smallest or least used room. That way by the time you have mastered it you will be ready for bigger things.