Commercial Ventilation Requirements Under Title 24
Ventilation is driven by people, not floor area. Section 120.1 derives the zone outdoor airflow rate from the expected occupant count the designer specifies, and where demand control ventilation applies it brings CO2 sensors with specified accuracy.
The rate follows expected occupancy
For spaces designed for an expected number of occupants, or with fixed seating, Section 120.1 determines the zone outdoor airflow rate by equation from the expected occupant count stated by the building designer. That figure is a design input with consequences: it sets the ventilation obligation for the life of the building.
It is also why a classroom or a restaurant dining room carries far more outdoor air than an office of the same size. The area is the same; the people are not.
Demand control ventilation, and its sensor rules
Where demand control ventilation applies, CO2 sensors are installed in each room meeting the Section 120.1(c)3 criteria, at no less than one sensor per 10,000 square feet of floor space.
The sensors themselves are specified, not left to the installer. Each must be certified by the manufacturer as accurate to within plus or minus 75 ppm at 600 and 1000 ppm concentration, measured at sea level and 25 degrees Celsius, factory calibrated, and certified to require recalibration no more often than once every five years.
The control target
The controls must maintain CO2 at or below 600 ppm plus the outdoor air CO2 concentration in every room carrying a sensor. Note the form of that: it is a figure above ambient, not an absolute ceiling, so the target moves with the outdoor air rather than being fixed.
It is acceptance tested
Demand control ventilation is functionally tested on site and documented on NRCA-MCH-06-A by a technician certified for mechanical acceptance testing. Sensor accuracy and calibration certification are part of what has to hold up, which is why specifying a compliant sensor matters more than it looks on a schedule.
Where this decides a project
On any occupancy with dense or variable occupancy — classrooms, dining, assembly, conference. Those are the buildings where the ventilation load is large enough that modulating it is worth the sensors, and where the acceptance test is most likely to be in scope.