The location of your fireplace should be determined by various factors such as size, design, and budget. It is important to have adequate space for both moving around in front of it while you are seated on a comfortable chair or ottoman. Generally speaking, a hearth that is 40-50 cm deep will allow enough room for most people even if there is also a mantelpiece above the firebox. If this sounds too small then go deeper but remember that going beyond 50 cm can affect how much heat gets into the adjoining living area so check with an installer before deciding what works well (or better) for your specific situation. A good rule of thumb when sizing up the fireplace is to imagine the size of a comfortable armchair that you would sit in front of.