The importance of insulation and some common issues is best shown using a case study. The example below illustrates how heat transfer occurs in a house. Actually heat transfer occurs anywhere and everywhere where there is a temperature difference between two objects and it flows from objects with higher temperature to lower, until both temperatures are equal. We say that warm air rises up or cold air flows down. In winter we say that cold enters the room or heat escapes or leaks. In summer heat enters room/house or warms up cool air. No matter how we call it, it is the same process and the same principle of heat transfer. Sometimes we like it, like direct sun in winter warming up rooms. But most of time it works against us and it is unwanted which is why we are doing what we are doing to slow it down - insulating, sealing gaps improving air circulation. It is important to understand that we cannot completely stop this process, even the best insulated and sealed house will continue to transfer heat in our out until it becomes as cold or as hot outside. Some houses will reach the temperature outside almost instantly, others might take long time. Making our houses keep the comfortable temperature as long as possible is what energy efficiency of our houses is about.