ACH (Air Changes per Hour) is the number of times air in a space is replaced each hour. Higher ACH = better ventilation.

How many ACH for different rooms?

Bedrooms: 4-6 ACH, Living rooms: 6-8 ACH, Kitchens: 8-12 ACH, Bathrooms: 8-10 ACH.

Air Changes Per Hour (ACH) Calculator

Air Changes Calculation

ACH is crucial for indoor air quality, removing pollutants, odors, and maintaining fresh air supply. Understanding air changes helps design ventilation systems that keep occupants healthy and comfortable.

What is ACH?

Air Changes per Hour measures how many times the total volume of air in a room is replaced:

1 ACH: Entire room air replaced once per hour
6 ACH: Complete air change every 10 minutes
12 ACH: Complete air change every 5 minutes

Calculating ACH

The formula is straightforward:

ACH = (CFM × 60) ÷ Room Volume
Room Volume = Length × Width × Height
Example: 200 CFM in a 12×15×8 room (1,440 cu ft)
ACH = (200 × 60) ÷ 1,440 = 8.3 ACH

Recommended ACH by Space Type

Bedrooms: 4-6 ACH
Living rooms: 6-8 ACH
Kitchens: 12-15 ACH
Bathrooms: 8-10 ACH
Home offices: 4-6 ACH
Garages: 4-6 ACH
Commercial kitchens: 30-60 ACH
Operating rooms: 20-25 ACH

Why ACH Matters

Indoor air quality: Removes pollutants, CO2, VOCs
Humidity control: Prevents moisture buildup
Odor control: Clears cooking smells, bathroom odors
Health: Reduces airborne pathogen concentration
Comfort: Prevents stuffiness and stale air feeling

COVID-19 Ventilation Guidelines

During the pandemic, higher ventilation was recommended:

CDC recommendation: 5+ ACH for occupied spaces
Schools: Aim for 6+ ACH in classrooms
Offices: Increase to 4-6 ACH minimum
Combined with filtration: MERV-13 or better filters