Active humidifiers can be described as:

Active humidifiers are devices specifically designed to add heat or water to the gas flow, ensuring that the delivered air or oxygen reaches a suitable temperature and humidity level. This function is crucial in medical settings, particularly for patients requiring respiratory support, as it mimics the natural conditions of the respiratory tract. By actively controlling the temperature and moisture content, these humidifiers enhance patient comfort and prevent complications that can arise from dryness, such as airway irritation or thickened secretions.

Other options do not accurately describe the operation of active humidifiers. For instance, while recycling exhaled heat and humidity does occur in some systems, it characterizes passive humidifiers rather than active ones. Similarly, merely using room temperature water is inadequate for maintaining the therapeutic levels of humidity. Lastly, active humidifiers typically require a power source to function properly, making them distinct from passive systems which can operate without electrical support. This highlights the importance of heat and moisture application in achieving effective humidification in respiratory care.