Final answer:
Houses in Northern European nations without heating systems rely on insulation and body heat to stay warm.
Step-by-step explanation:
In some Northern European nations, homes are being built without heating systems of any type.
These homes are very well insulated and are kept warm by the body heat of the residents. When the residents are not at home, it is still warm in these houses due to the insulation retaining the heat that was generated when the residents were present.