As I’ve explained, the house is going to need some major work not least the addition of a central heating system.  This is a large change and will have a significant effect on the whole energy use of the house.  This is important for how I decided to model the property….

The first thing we do to analyse a property, once the survey has been carried out and the model calibrated, is to apply individual measures to test their individual effects. In this case since one of the measures (a new central heating system) is going have such a large effect on most of the others, and also since the new central heating system is definitely going ahead, it would see sensible to apply it to the base case and evaluate all the other measures against the property with a new central heating system.

I can still work out the benefit of the central heating system by either carrying out that analysis first or by putting in an ‘if I don’t change the central heating system’ measure.  This latter one will just give some negative savings (I hope!) equal to the positive savings I would have got by doing it the other way round.

We often do this when modelling changes that we know will effect many other things or are definitely going ahead.