The air inlet and vents have screens to keep out insects. The natural chemical and biological reactions of the aerobic decomposition process generate some heat, which in turn creates convection currents for air circulation and water evaporation, although this may not be sufficient in some locations. At a minimum, a vertical chimney vent is needed to induce air flow through the system. Many commercial units use an electric fan to maintain air circulation. To speed up water evaporation and maintain the proper temperature for the decomposition process, many commercial units have a thermostatically controlled electric heating element.
Some units also have a mechanism that regularly stirs or mixes the compost.
If the vent chimney gets sun exposure, painting it black will increase natural air convection. These systems can be installed in areas where there is no electric utility service. A properly operating composting toilet will produce odorless carbon dioxide, nitrogen, and water vapor. If there is too much moisture or not enough oxygen, anaerobic bacteria, which live without oxygen, will become active. Anaerobic bacteria produce various gases that give off odors.