ASHRAE 241 is the first ASHRAE standard aimed specifically at controlling infectious aerosols indoors. It sets how much effectively clean air each occupant should receive during periods of elevated risk and how buildings plan, commission and operate for it. Related ventilation rules sit in ASHRAE 62.1.

Is ASHRAE 241 mandatory?

Only where an authority adopts it. Otherwise ASHRAE 241 is voluntary, and the AHJ decides when the infection risk mode is triggered. Many owners use it as a planning benchmark for health care, schools and offices even without a mandate.

Does CO2 measure infection risk directly?

No. CO2 shows exhaled air building up, which reflects outdoor air per person, but it misses filtration and air cleaners that also count toward clean airflow. It remains a useful operating signal through CO2 monitoring, read alongside equipment status.

What does a readiness plan contain?

A building readiness plan documents how a building will meet its clean airflow target: the systems used, their settings for infection risk management mode, and how performance is checked. Commissioning then confirms the plan, and monitoring data helps show the mode works when activated.

Glossary

Education, airports and industry

What is ASHRAE 241?

Definition

ASHRAE Standard 241 sets minimum requirements to reduce airborne transmission of infectious aerosols indoors, expressed as a target rate of equivalent clean airflow per occupant.

Where it applies

ASHRAE published it on 7 July 2023. It covers new and existing buildings and major renovations, across residential, office, school and health care settings.

Core requirements

Per ASHRAE, the standard is built on these elements:

A target for equivalent clean airflow per occupant, delivered by outdoor air, filtration and air cleaning
An infection risk management mode for periods of elevated risk, with the authority having jurisdiction deciding when it applies
Requirements for filtration and air-cleaning technologies
Planning and commissioning, including a building readiness plan

Checking the mode in occupied rooms

Clean airflow is set at design, but occupancy moves. Aqueduct overlays CO2 with occupancy per zone and counts exposure in zone-hours, a practical check on whether outdoor air keeps up with people once the risk mode is on. Smart Controls can raise outdoor air or fan speed over BACnet or Modbus where control is enabled, with owner approval.

What is ASHRAE 241?

Where it applies

Core requirements

Checking the mode in occupied rooms

ASHRAE 241: common questions

See Aqueduct on your own facility.