Which of the following is NOT a common method of greenhouse heating?

Ceiling fans are primarily used for air circulation and temperature regulation within a greenhouse, but they do not provide heat themselves. Instead, their function is to help distribute warm air that has been generated by other heating systems, promoting even temperatures throughout the space. In contrast, electric heaters, under-bench heating mats, and gas heaters are all direct methods of generating heat to maintain ideal growing conditions for plants. Using ceiling fans effectively can complement heating systems by preventing hot spots and improving overall air movement, but they are not a heating method.