Radiant or convection
Radiant heaters warm people and objects directly in their line of sight. Convection heaters warm the surrounding air. The distinction matters when considering how you occupy a space. Source: doe
Portable or installed
Small space heaters may be portable, while radiant systems can also be built into floors or panels. Installation requirements depend on the system. Read the instructions for the specific equipment. Source: doe Source: radiant
Read the specification
Make a shortlist of questions: where may the heater be used, how is it mounted, what electrical supply does it need, and what clearances does its manual require? Record the answers from the exact model documentation. Source: editorial