About

Proper ventilation is not merely about comfort; it is a critical component of occupant health, pathogen control, and CO2 management. This tool calculates the required airflow in Cubic Feet per Minute (CFM) or Cubic Meters per Hour (m³/h) using two distinct methods: the Air Changes per Hour (ACH) method and the ASHRAE 62.1 Ventilation Rate Procedure (VRP). The ACH method focuses on replacing the entire volume of air in a room a specific number of times per hour, which is essential for dilution ventilation in medical or industrial settings. The VRP method accounts for the number of occupants and the floor area, ensuring adequate fresh air per person to minimize bioeffluents.

Inadequate ventilation leads to Sick Building Syndrome, characterized by fatigue, headaches, and respiratory issues. Conversely, over-ventilation results in unnecessary energy costs for conditioning outside air. Engineers and facility managers use these calculations to size fans, ducts, and air handlers. This calculator includes a reference database derived from ASHRAE standards and medical guidelines for environments ranging from residential living rooms to hospital isolation wards.

Formulas

The calculation of required airflow relies on the room volume and the target frequency of air replacement.

1. Air Changes per Hour (ACH) Method:

V × ACH60 = CFM_req

Where V is the room volume in cubic feet and 60 converts hours to minutes.

2. Ventilation Rate Procedure (ASHRAE 62.1):

CFM_vrp = (N_p × R_p) + (A_z × R_a)

Where N_p is the number of people, R_p is airflow per person, A_z is the zone floor area, and R_a is airflow per unit area.

Reference Data

Room Category	Target ACH (1/h)	CFM per Person	CFM per ft²
Residential Living Room	0.35	5	0.06
Residential Kitchen	5.0	20	0.12
Office Space	2 - 3	5	0.06
Classroom	3 - 4	10	0.12
Restaurant Dining	8 - 12	7.5	0.18
Commercial Kitchen	20 - 30	20	0.20
Hospital Patient Room	4 - 6	25	-
Operating Room	15 - 25	30	-
Laboratory	6 - 12	20	0.18
Gymnasium	4 - 6	20	0.12
Restroom (Public)	10 - 15	-	50 (per unit)
Conference Room	4 - 8	5	0.06

Frequently Asked Questions

[{"question":"Why is the calculated CFM different between ACH and Per-Person methods?","answer":"The ACH method is volume-based, focusing on diluting pollutants in the entire air mass. The Per-Person (ASHRAE 62.1) method is load-based, focusing on providing enough fresh oxygen for occupants. For design purposes, engineers typically calculate both and select the higher value to ensure compliance with the strictest safety standard."},{"question":"Does this calculator account for air recirculation?","answer":"No. This tool calculates the "Outside Air" or "Effective Ventilation" requirement. In modern HVAC systems, total supply air is a mix of recirculated air and fresh outside air. The value generated here represents the fresh air component required to maintain air quality, or the total flow if using 100% fresh air systems (common in hospitals)."},{"question":"How does ceiling height affect the requirements?","answer":"Ceiling height directly increases the room volume (V). In the ACH method, a higher ceiling means a larger volume of air must be moved to achieve the same turnover rate, requiring larger fans. In the per-person method, ceiling height often has less impact unless the volume helps buffer pollutant buildup."},{"question":"What is a safe ACH for a home office?","answer":"For residential spaces, ASHRAE 62.2 generally suggests a baseline, but for a dedicated home office, 0.35 ACH is the minimum standard. However, increasing this to 3 or 4 ACH (similar to commercial standards) during working hours can significantly reduce CO2 levels and improve cognitive function."}]