Before you purchase an existing home, you can (and should) take a look at one of the previous owner's heating bills. While this will not tell you directly how the home's energy efficiency compares to similar homes, it will give you a general idea and it will allow you to weed out homes that are seriously inefficient.

With a new home, things are different, because historic data is not available. And yet, the assumption that any new home by default will be efficient turns out to be invalid. You need to look at a few things, and while you will not have the time and tools to make this an exact science, a violation of more than a few guidelines presented in this section should be a warning sign for any buyer who is concerned about energy efficiency and a future heating bill.