An average size house uses about 27% of all energy usage for heating and a/c and the bigger the house, the more energy is used.
21% of energy used is from appliances. Water heaters are a big culprit of energy usage and not only that, but they are also a huge culprit of water usage. Again, the bigger the house(as well as more people in the home), the more water is used. Really big houses are not a wise, eco-friendly way of living.