Our houses use the sun’s energy for a good bit of their heat. Most rooms have large south facing windows which soak in winter sunlight. Not only do these windows help heat the house, they also flood it with light. The result is a brighter, more enjoyable, more livable space.
Being conservative with non south-facing windows is also important. Even though windows are much tighter now than they used to be, they still aren’t good insulators. North facing windows never get direct sunlight, so they are cold holes in the house during winter months. Because of its height in the summer, the sun won’t heat south facing windows. But the sun’s low position in the morning and evening will cook a house with too many east and west windows. That’s why non-south facing windows bring down the efficiency of the house and should be used carefully.