What type of heating methods does indirect heating typically involve?

Indirect heating typically involves utilizing radiated heat. This method relies on the transfer of heat from a heat source to a substance without direct contact with the heating medium. In this way, the heat is radiated or transferred through a medium, allowing the substance being heated to accumulate the energy without being exposed to the flames or direct heat.

Radiant heating systems, for instance, warm the surrounding environment by emitting infrared radiation, which is absorbed by objects and surfaces, thus providing a comfortable heating effect. This type of heating is common in various systems, such as space heaters that use panels or floors heated by radiant energy.

The other heating methods presented do not fit the definition of indirect heating. For example, direct heat from a flame involves direct contact with flames, which is characteristic of direct heating. Compressed air heating would be more aligned with forced air systems rather than indirect methods, and acoustic energy heating is a unique form of heating that utilizes sound waves, which is not relevant in the context of standard indirect heating practices.