Heat exchangers transfer thermal energy between fluid streams as their primary function, while equipment classified here actively changes the temperature of a material being processed (e.g., a kiln firing ceramics or a test chamber cycling a product through temperature extremes). If the unit's principal function is processing or treating a material rather than exchanging heat between streams, this residual heading is the more appropriate classification.

Semiconductor processing equipment such as diffusion furnaces and chemical vapor deposition reactors may fall here if their primary function is thermal treatment of materials, but they can also be classified under dedicated semiconductor manufacturing equipment headings depending on their specific design and function. The classification analysis should focus on the machine's principal function and the heading that most specifically describes it.