This is incredibly naive. The only non-naive thing is that it is proportional to ΔT, which is simple Physics. I don’t know why you need to quote building scienc

This is incredibly naive. The only non-naive thing is that it is proportional to ΔT, which is simple Physics. I don’t know why you need to quote building science here. For non naive calculation, one would expect using real world data to estimate the actual weighted average. I mean it is ok to have a naive guesstimate, or to sound better, a Fermi estimate. But for order of magnitude guesstimate, just use 1 sig fig to convey you really don’t have that much confidence. Also I think while providing a ratio is technically answering the question, but people probably expect the absolute scale, in terms of $ or may be a ratio comparing to annual spending (given a country.) I think in short this is not a simple question and we should not pretend it to have simple answer.