This blog post is in response to the following question; “Do I need a temperature difference to do thermography on a building? If so, how much?”
Yes, you definitely do need a temperature difference to do thermography on a building, at least if you want to find something. The only real exception to this is where you are trying to locate problems due to a difference in thermal inertia, for instance a roof survey.
Heat will spontaneously flow from higher to lower temperatures, so from the hot side of a building to the cold side. This means that bad insulation and thermal bridges will allow the heat to flow faster. Bad insulation will cool the hot side down quicker, and heat the cold side up faster. This mean that it will show up as a cold spot on the hot side, and a hot spot on the cold side. If there is no temperature difference, then there will be no heat flow, and nothing will be visible, it will appear consistent. For air leakages, you will find the same problem. Air leakages can be located on the principle that the air is either hotter or colder, and therefore either heating or cooling the surfaces that it strikes. if the air temperature is the same both inside and outside the leak may not be visible.
I would advise a temperature difference of 10 degrees C. It does not really matter if the inside is hotter or colder. In some locations it will be easier to heat, and in others it will be easier to cool.
HOW MUCH TEMPERATURE DIFFERENCE DO YOU USE WHEN CARRYING OUT THERMOGRAPHY?