Under what condition is taking return air from a kitchen not prohibited?

Taking return air from a kitchen is allowed when it is at least 10 feet from cooking appliances. This requirement is established to ensure proper air circulation and reduce the risks of contamination and the carrying over of cooking odors or grease particles into the building's air supply. The distance helps to maintain air quality and prevent any adverse effects on the HVAC system's performance. Proper separation from cooking equipment ensures that the air being circulated through the system does not negatively impact air quality in other areas of the building, particularly in spaces dedicated to occupancy or sensitive uses.

Other conditions presented in the options do not align with code standards or may present additional challenges. For example, using return air from a kitchen to serve a bathroom or for heating purposes may not provide adequate air quality or create undesirable airflow patterns. Additionally, an open design does not inherently qualify for taking return air from a kitchen, as the proximity to cooking sources remains a critical factor.