A floor furnace can be installed under all the following conditions EXCEPT:

A floor furnace is typically designed to be installed in specific conditions to ensure safety and efficiency. The option regarding placement on a concrete pad is not permissible because floor furnaces are generally not meant to be directly installed on a concrete surface. This is due to the need for proper ventilation and air circulation, which can be obstructed when the furnace is placed directly on a solid, non-ventilated surface like concrete.

In contrast, wooden floors can support the installation of a floor furnace, provided there are necessary safeguards in place to prevent combustion risks. Additionally, floor furnaces can be installed in non-combustible environments and enclosed basements, which typically allow for appropriate clearance and air flow, essential for safe operation.

Choosing to install a floor furnace on a concrete pad poses risks related to heat retention and potential damage to both the furnace and the concrete, making it unsuitable as a installation condition.