What is ASHRAE 241?
ASHRAE 241 is the ASHRAE standard Control of Infectious Aerosols, published in 2023. It sets requirements for equivalent clean airflow per occupant by space type, which can be met through outdoor air, filtration and air cleaning, and asks buildings to have a plan for operating in an infection risk management mode.
What it is
ASHRAE 241 introduced equivalent clean airflow as the key measure. It counts outdoor air, filtered recirculated air and air treated by cleaning devices toward a per occupant target that depends on the space type.
The standard requires a building readiness plan that describes how the building will meet the targets when infection risk management mode is in effect. The mode is decided by the owner or authorities, often during periods of elevated risk.
Because outdoor air is only one route, teams can combine ventilation with filtration and air cleaning to meet targets with less energy.
Where it is used
Schools, offices, healthcare, public buildings and other spaces where people gather. The standard is voluntary unless adopted by an authority or required by an owner.
Many owners use it as a reference for preparedness even when it is not required.
How it is measured
Equivalent clean airflow is assessed from design data and verified through operation.
- Outdoor airflow per space
- Filter efficiency and recirculated airflow
- Air cleaner capacity and performance
- Occupancy per space during occupied hours
How Aqueduct helps
Aqueduct supplies per-room air records and ventilation response in occupied hours.
- aQ AirSafe CO2, particulate and occupancy sensing per room
- Ventilation and filtration response flagged when a room drifts
- Outdoor air increased where control is enabled, with owner approval
- aQ Assurance records of room conditions during risk periods