The volume and structures of the sauna affect the selection of heater power. An average of 1 kW of heater power is required for each cubic metre of sauna volume. The power requirement increases if there are window surfaces or heat-storing surfaces such as brick, concrete or massive logs in the sauna.
One square metre of stone, glass or similar non-insulated surface increases the heater power requirement as much as if the sauna room volume were increased by 1.2 cubic metres. If the interior walls of the sauna room are made of non-insulated logs, the corresponding factor is 1.5.
If the heating capacity is too small, the heater needs to be heated longer and more intensely, which reduces its life span.
Calculate the volume here