Ventilation Rate Calculator Formula
Understand the math behind the ventilation rate calculator. Each variable explained with a worked example.
Formulas Used
People Component
people_cfm = occupants * cfm_per_personArea Component
area_cfm = floor_area * cfm_per_sqftTotal Outdoor Air
total_cfm = occupants * cfm_per_person + floor_area * cfm_per_sqftVariables
| Variable | Description | Default |
|---|---|---|
floor_area | Floor Area(sq ft) | 1000 |
occupants | Number of Occupants(people) | 10 |
cfm_per_person | CFM per Person(CFM) | 5 |
cfm_per_sqft | CFM per Sq Ft(CFM) | 0.06 |
How It Works
ASHRAE 62.1 Ventilation
Outdoor Air = (People x CFM/person) + (Area x CFM/sqft)
ASHRAE 62.1 uses a two-part calculation: a per-person rate for bioeffluents and a per-area rate for building emissions. Office spaces typically use 5 CFM/person and 0.06 CFM/sqft.
Worked Example
1,000 sq ft office with 10 occupants.
- 01People = 10 x 5 = 50 CFM
- 02Area = 1000 x 0.06 = 60 CFM
- 03Total = 50 + 60 = 110 CFM outdoor air
Frequently Asked Questions
Why are there two components?
The per-person rate handles CO2 and odors from occupants. The per-area rate addresses off-gassing from building materials, furniture, and finishes regardless of occupancy.
Is this the total supply air?
No, this is only the outdoor (fresh) air portion. Total supply air also includes recirculated air needed for temperature control, which is typically much higher.
Ready to run the numbers?
Open Ventilation Rate Calculator