Figure out how much you or your customer will pay each year for their space and water heating. Specify the location, energy source, age, and efficiency rating of the space or water heating system you are examining. Based on that info, the app will generate the estimated annual energy cost and CO2 emissions that a homeowner can expect. The app always provides a comparable Energy Star system to serve as a reference for your results. You can also enter two systems and compare results side-by-side.