Indoor Air Quality Ventilation Rate Calculator
Calculate the minimum outdoor air ventilation rate required for acceptable indoor air quality based on ASHRAE Standard 62.1 (Ventilation for Acceptable Indoor Air Quality). The calculator uses the Ventilation Rate Procedure combining people-related and area-related components.
Per-person outdoor air requirement (ASHRAE 62.1 Table 6-1)
Per-unit-area outdoor air requirement (ASHRAE 62.1 Table 6-1)
ASHRAE 62.1 Table 6-2 — affects zone minimum outdoor air
For single-zone systems use 1.0; for multi-zone use ASHRAE 62.1 Section 6.2.5
Results will appear here.
Formulas Used (ASHRAE 62.1 Ventilation Rate Procedure)
Step 1 — Breathing Zone Outdoor Airflow:
Vbz = Rp × Pz + Ra × Az
- Vbz = Breathing zone outdoor airflow (cfm)
- Rp = People outdoor air rate (cfm/person) — ASHRAE 62.1 Table 6-1
- Pz = Zone population (number of occupants)
- Ra = Area outdoor air rate (cfm/ft²) — ASHRAE 62.1 Table 6-1
- Az = Zone floor area (ft²)
Step 2 — Zone Outdoor Airflow:
Voz = Vbz / Ez
- Ez = Zone air distribution effectiveness (ASHRAE 62.1 Table 6-2)
Step 3 — System Outdoor Airflow:
Vot = Voz / Ev
- Ev = System ventilation efficiency (1.0 for single-zone systems)
Steady-State CO₂ Concentration:
Ci = Co + (G / Vot) × 10⁶
- Co = Outdoor CO₂ concentration (400 ppm assumed)
- G = CO₂ generation rate (0.0106 cfm/person for sedentary adults)
Air Changes per Hour:
ACH = (Vot × 60) / Vroom where Vroom = Floor Area × 9 ft
Assumptions & References
- Standard: ASHRAE Standard 62.1-2022, Ventilation and Acceptable Indoor Air Quality in Residential Buildings — Ventilation Rate Procedure (Section 6.2)
- Outdoor air rates (Rp, Ra) are taken from ASHRAE 62.1 Table 6-1 for common space types. Custom values can be entered manually.
- Zone air distribution effectiveness (Ez) values are from ASHRAE 62.1 Table 6-2 based on supply air delivery method and temperature differential.
- System ventilation efficiency (Ev) is 1.0 for single-zone systems. Multi-zone recirculating systems require the more complex procedure in ASHRAE 62.1 Section 6.2.5.
- CO₂ generation rate is 0.0106 cfm/person (≈ 0.005 L/s·person) for sedentary adults per ASHRAE 62.1 Informative Appendix B.
- Outdoor CO₂ is assumed to be 400 ppm (current global average).
- Ceiling height for ACH calculation is assumed to be 9 ft (standard commercial). Adjust manually for other heights.
- CO₂ thresholds: <1,000 ppm = excellent; 1,000–1,500 ppm = acceptable; >1,500 ppm = poor (OSHA/NIOSH guidance).
- This calculator applies to commercial and institutional buildings. Residential ventilation is governed by ASHRAE 62.2.
- Results represent minimum required outdoor air. Local codes, energy recovery, filtration, and occupant health needs may require higher rates.