According to Section 407.4.1.7, a recirculating room HVAC unit serving a single patient room is permitted to provide the recirculated portion of the required air changes. Which of the following is a requirement for such a unit?

• It must provide all required outdoor air changes for the space.
• It must serve multiple spaces to be efficient.
• It may receive nonfiltered outdoor air directly.
• A filter must be located upstream of any cold, condensing surface.