Healthy Buildings FAQ

Stanford Building Ventilation — COVID-19 FAQs

What has Stanford done to ensure building ventilation is prepared for the return of on-site faculty, staff, and students?

To supplement primary COVID-19 safety measures (i.e., vaccination, universal masking, health screening), the following ventilation-related efforts have been implemented as part of building restart procedures:

  • Mechanical heating, ventilation, and air conditioning (HVAC) systems have been optimized per industry standards and guidelines, with strategies including:
    • Ensuring proper outdoor air exchange:
      • Increasing daily operating hours (by as much as 50%).
      • Maximizing the amount of outdoor air exchange in areas where larger groups gather (e.g., housing, dining, classroom, performing arts, and athletics facilities).
    • Upgrading high-efficiency air filtration (up to MERV-13) where possible to further optimize general indoor air quality. NOTE: Given above air exchange provisions, air filtration upgrades are primarily helpful with building resiliency during wildfire smoke events.
  • HVAC systems are kept on routine preventative maintenance schedules to ensure fans and air filtration continue operating effectively and efficiently.


What if my space is naturally-ventilated?

Natural ventilation means an indoor space receives fresh outdoor air by opening windows. If windows are inoperable, contact your building manager for assistance.

For multiple occupant areas where portable fans are used, avoid blowing air from the breathing zone of one person to the breathing zone of someone nearby.

  • Where possible, securely position the portable fan at the window opening and orient so that the air is blowing to the outside, and
  • Avoid positioning fans that push air horizontally from person to person in the room.
  • For ceiling fans, ensure air flow directionality is upwards where possible.

Flowchart about air ventilation

Talk with your Building or Zones Manager to learn more about the ventilation design for spaces in your building.


How about portable air purifiers?

Portable air purifiers are effective at reducing airborne aerosols and dust indoors; nonetheless, these devices are not needed in most campus spaces because of the existing building features that provide the necessary outdoor air exchange (by mechanical ventilation or by operable windows).

  • HEPA air purifiers are recommended for use in specific higher-risk settings (e.g., non-hospital clinical spaces) where active procedures may result in respiratory aerosol generation. EH&S can review these spaces on a case-by-case basis as needed.

Where local groups wish to purchase portable air purifiers for comfort purposes, below are recommended selection criteria:

  • Provides multi-stage filtration: 1) Pre-filter, 2) HEPA-rated filter, 3) Activated carbon filter (optional),
  • Does NOT contain UV light or ionizer features,
  • Multiple fan speed settings,
  • Quiet,
  • Energy efficient, and
  • CADR (clean air delivery rate) appropriate for room size.


Room Square Footage (10 ft ceiling): Recommended CADR (Clean Air Delivery Rate):
<100 sq ft At least 70 cfm (cubic ft/ minute)
101-500 sq ft At least 330 cfm
>500 sq ft Multiples of at least 330 cfm

Reference: Harvard/ CU Boulder Portable Air Cleaner Calculator v1.3

For a list of California Air Resources Board (CARB)-approved devices, refer to their website:


What about wildfire smoke?

University buildings with mechanical ventilation provide filtered air that help to minimize the infiltration of wildfire smoke particulate matter into the building. Units with naturally-ventilated areas are encouraged to communicate with their management for guidance on wildfire smoke resiliency planning.