Unlike vehicles where it is easy to compare efficiency by comparing the mileage (expressed in either miles per gallon or litres per 100 km), comparing efficiency of two houses - or comparing efficiency before and after improvements to a house - is much more difficult.  If a homeowner makes an investment in improved energy efficiency it is difficult to compare the effect of the improvement from one month to the next due to seasonal changes.  Comparing a months worth of post-improvement energy consumption with the same month of the previous year or even the average of that month over the previous X years is an improvement but still doesn't really provide a direct “apples to apples” comparison as the month immediately following the improvement may have been warmer or colder than usual.  read more... »