Thermal (Infra-Red) Imaging
There are many firms that tout the new fancy Infra-Red Camera (imager) and the many training seminars they have gone to and seem to think they are the best thing since sliced bread. Thermal Imagers are indeed a very useful tool but you really need to fully understand what the imager sees to understand what it can do, and more importantly what it can’t do. There are times and conditions under which the imager is blind, and there are also conditions which will “Fool” the imager into showing artifacts that are not really there. Additionally some things that look really really weird are just fine. Again you need to know what the imager is seeing, and what you SHOULD be seeing. Classroom theory is a nice thing, but Inspections by Bob believes that experience and an understanding of what is going on is more important for the home inspector to be able to “read” the images the thermal imager provides.
Yes, Inspections by Bob has a Thermal Imager, and we don’t use it very much, but when we do use it, it provides a view that no other tool could. Also please note that our STANDARD contract specifically states that we cannot address those items which we cannot SEE. A thermal imager allows us to see indicators of possible issues, but we still cannot see through walls. We can see symptoms that may be indicators of something inside the wall, but the only way to see inside the wall for sure is to cut a hole…and we don’t do that.
Thermal Imagers see radiant Heat, and can measure the amount of heat that they are seeing ,very precisely… routinely to less than 1/10th of 1 degree Celsius.
There are 4 Cups in this picture: one full of cold water, one partially full of warm water, one full of warm water and one empty. Can you tell which cup is which? Notice that the EMPTY cup blends into the image rather well. It is much easier to see something that is WARM.
If there is no temperature difference (the empty cup) there is nothing to see. The larger the difference, the easier it is to see.
Also note that this image is a COMBINATION of Thermal and Visible. In a pure thermal image, the empty cup would be invisible (which is what happens when the inside and outside are the same temperature)
That said, a thermal imager can be configured to see very very small differences in temperature. The image to the right is of a carpeted floor that was just walked on in bare feet. The imager is seeing where the feet warmed the floor temporarily; these images fade very quickly. Technology like this is used by the military and police to track people and vehicles by their thermal impact on their surroundings, but their imagers are far more sensitive.
How does this help the home buyer, as thermal imaging is not part of a normal inspection? If we suspect a problem we may take out the imager to confirm something, or that other indicators point to. Recently in a newly constructed house the builder had to open up a wall to reconnect the heat pump refrigerant lines. The wall “felt” cold, as did the room. Lets start with what a “Normal” wall looks like.
You can see the wall studs, barely, but in the majority of the wall there is not much difference between the insulated section and the stud section. Where two wall sections meet there is a bit more difference, but not a lot. It would probably be rated as “Acceptable”.
However, looking at the wall NEXT TO this one, we see something different.
The large sections show what appears to be voids in the insulation where the contractor likely compressed the insulation to put the refrigerant lines in (The Heat pump compressors were directly behind this wall section) and then never “re-fluffed” the insulation. This is what we suspect is behind the wall, but without cutting a hole in the wall we can’t be sure. The written report stated that Bob thought there was an abnormality in the wall that made sections much colder than the rest of the wall.
Bob also saw the condition (shown right) where an outside corner was much colder than the surrounding wall sections. He suspected that there was an air leak at the sill plate and that he was seeing the effects of a draft. You can see how the (suspected) draft starts in the corner and extends out following the slight gaps caused by edge stapling the insulation. Moisture can cause a similar image, but in this case the moisture meter said that the wall at the corner had the same moisture content as the rest of the wall.
Note: We started with a standard inspection, something was suspected, our standard observations (hands, eyes) led us to believe there was a possible hidden issue. The thermal imager allowed us to “see” what we had felt with our hands. We cannot SAY for certain what the issue is that is causing these images without cutting holes as we still can’t see through walls. We use the thermal imager as a tool, just like an outlet tester, moisture meter, thermometer, flammable gas detector and the myriad of other things in our tool kits.
Using a thermal imager is not practical on every inspection as it takes a lot of time to setup properly. And if the outside is the same temperature as inside, the camera will be blind (remember the empty foam cup?). There actually is a standard that describes the procedure for inspecting insulation in Frame buildings (ASTM C 1060) and it says (in far too many words) that you really need a MINIMUM of 18°F difference between the interior and exterior, with a recomended interior temperature near 70. That means that the EXTERIOR temperature really needs to be below 50 or above 80 for adequate images. The ASTM standard also says that you can adjust the interior temperature as needed, but it must be STABLE and recomends a 3-HOUR pre-inspection conditioning period.