The rankings are based on a home's actual consumption history, and how the ranking is calculated changes based on what you're looking at.
If you're looking at electricity, gas, or water, then homes are ranked based on raw consumption alone, using simple arithmetic.
If you're looking at CO2e, there's a bit more math. For each KWh of energy you consume, a power plant somewhere generates some greenhouse gas, and the EPA measures the amount and publishes a series of conversion factors. Using those, we do some multiplication and add up how much CO2 you generate based on your electricity, water, and natural gas usage. These rankings are not of any official use and are not certified by anyone. Please use them as a rough guideline only.
If you've selected the "Normalize Energy Usage per 1000 sq. feet." option, then we normalize consumption based on the size of the home, and rank homes based on usage per 1000 sq ft.
For a single home, there is a download link to the data on the Home Energy Report.
For mulitple homes, the easiest way is to create a group (you will need to login) , then from the groups page there is a link where you can download all data about your group.