why do you need that you from my termofluids classes you should be able to calculate the heat loss for a given Delta T by taking a ball park figure for the materials ie so many square meters of brick Glass etc.
You use it when you don't know the material (because you're surveying an old house) or you don't know the delta-T (because you're looking for a hidden fire, grow op, etc).
Or you're trying to track down head loss caused by construction flaws, especially leaks and drafts caused by cracks or gaps.
Also leaks caused by improperly installed power points.
Missing or settled insulation is also common.
