Ventilation Rate Calculator – Calculate Required Airflow (ACH & CFM) per ASHRAE

Design healthy indoor spaces with our Ventilation Rate Calculator. Enter room volume, occupancy, and space type to calculate the required air changes per hour (ACH) and CFM airflow rate per ASHRAE 62.1 standards.

Length

Width

Height

Unit

Room Type

Number of Occupants

Results

Enter room dimensions and click Calculate to see results

Understanding Ventilation Requirements

Proper ventilation is essential for maintaining indoor air quality (IAQ). ASHRAE 62.1 provides guidelines for minimum ventilation rates in buildings.

ACH (Air Changes per Hour): Number of times the air in a room is replaced per hour.
CFM (Cubic Feet per Minute): Volume of air flow rate.
Formula: CFM = (Room Volume × ACH) / 60

Note: These are minimum requirements. Consider additional ventilation for high-pollutant activities, climate conditions, or specific health requirements.

How to Calculate Ventilation Rate

Enter Room Dimensions

Input length, width, and height of your space in feet or meters.

Select Room Type

Choose from preset room types with ASHRAE-recommended ACH values.

Get CFM Requirements

See required airflow in CFM, L/s, and m³/h for HVAC sizing.

Why Use This Ventilation Rate Calculator

ASHRAE 62.1 Compliant

Uses industry-standard ACH values from ASHRAE 62.1 for various room types.

Dual Calculation Methods

Calculates based on both room volume (ACH) and occupancy (CFM/person).

Multiple Unit Output

Get results in CFM, liters/second, and cubic meters/hour for international use.

14 Room Type Presets

Pre-configured ACH values for bedrooms, kitchens, offices, labs, and more.

ASHRAE Recommended ACH Values

Room Type	ACH	CFM/Person	Notes
Bedroom	5	10	Sleeping area
Living Room	4	15	General occupancy
Kitchen	7	20	Cooking pollutants
Bathroom	8	25	Moisture control
Office	6	20	Work environment
Laboratory	10	30	Fume extraction

Frequently Asked Questions

What is a good ACH for a home?

For whole-house ventilation, 0.35-0.5 ACH is typical for energy efficiency. Individual rooms need higher rates: bathrooms 8 ACH, kitchens 7 ACH, bedrooms 5 ACH, and living areas 4-5 ACH.

How do I calculate CFM for a room?

CFM = (Length × Width × Height × ACH) ÷ 60. For a 12×15×8 ft bedroom at 5 ACH: (12×15×8×5)÷60 = 120 CFM required for proper ventilation.

What is ASHRAE 62.1 standard?

ASHRAE 62.1 is the industry standard for ventilation system design, specifying minimum outdoor air rates for acceptable indoor air quality in commercial and institutional buildings.

How much ventilation does a bathroom need?

Bathrooms require 8 ACH or 50 CFM minimum for intermittent fans, 20 CFM continuous. For a 6×8×8 ft bathroom: (6×8×8×8)÷60 = 51 CFM minimum exhaust fan capacity.

What happens if ventilation is too low?

Inadequate ventilation causes poor indoor air quality, moisture buildup, mold growth, CO2 accumulation, odors, and health issues like headaches and respiratory problems.

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