In some of the newest and recently renovated houses each apartment has its’ own ventilation unit, These units increase the living comfort and give tenants the possibility to control the ventilation of their own apartment.  Where the traditional ventilation system operates at a certain level in each apartment,,ventilation units in apartments make it possible to take into consideration the individual ventilation needs of the tenant and the apartment. For instance in apartments on the southern side of a building the ventilation need is often higher than on the northern side of the building. In most cases ventilation units use electricity to heat up the fresh air and, therefore, they should not be operated at high power during the winter season. Units’ electricity costs are included in the apartment’s electricity bill.