We distinguish between two heating systems: the collective system, in which the same type of installation is shared by one or several buildings with more than one dwelling, and the individual system, in which the installation is independent from the rest of the dwellings in the building.

We do not consider as having a heating system or installation those dwellings that exclusively possess a mobile or fixed appliance which enables the temperature of one or all the rooms to be raised, including mobile electric radiators. These cases are included in the heading for occasional heating.