>Houses were build with the assumption, that they are heated. Yes and no. It depends on the country and areas within it and it applies mainly to houses built

>Houses were build with the assumption, that they are heated. Yes and no. It depends on the country and areas within it and it applies mainly to houses built in the last 60-70 years or so, maybe a few more years back in cities (for heating with radiators) before that time many, many houses were (poorly) heated by fireplaces and/or stoves. Besides, the permeability of the building materials was traditionally much better, and windows/doors were leaky, guaranteeing a much better ventilation. At least here in Italy the heating was a luxury until well after World War II, particularly in the country and in small vilages, anecdotally my family used to have a house in a small village in central Italy where the heating until the '70's was based on the devices that can be seen here (Italian): https://www.muet.it/storie/tutte-le-storie/item/il-riscaldamento-domestico.html https://www.muet.it/storie/tutte-le-storie/item/il-riscaldam... Particularly the kitchen and dining room was heated by the "stufa economica" that was also used to cook meals, the sitting room had a fireplace that heated also (a little) the bedroom behind it, and there was another large bedroom heated by a "stufa in terracotta", having a "prete" for each bed was needed. The house was anyway very, very cold, particularly at night/early morning.