ACH Calculator

Calculate the ACH in any room or building to ensure optimal air quality.

Airflow in CFM (cubic feet per minute)


Room Volume (cubic feet)



Air Changes per Hour (ACH):


Learn how we calculated this result below.

Air Changes Per Hour (ACH) Calculator [Free]

Measuring air changes per hour (ACH) is crucial for maintaining healthy indoor air quality and ventilation system performance, especially in buildings like hospitals, office buildings, and homes. Our Air Changes Per Hour Calculator is designed to help you calculate the ACH in any room or building, ensuring optimal air quality and compliance with healthcare standards. Use this tool to determine the number of times air in a defined space is replaced with fresh air in one hour. Understanding the air exchange rate is vital for ventilation planning, HVAC system design, and ensuring safe, clean air.

How to Use Our Free ACH Calculator

Similar to our HVAC CFM calculator and load calculator, our free Air Changes Per Hour Calculator makes it easy to determine the number of air changes needed for proper ventilation based on a formula using basic room dimensions. To use our free ACH Calculator, you need the room's volume and the total airflow rate (measured in cubic feet per minute) of your ventilation system. The ACH is calculated using the formula:

  • ACH = CFM x 60 / Room Volume (Area x Height)

This formula calculates the air change rate or how many times the air within a room is replaced in an hour.

Step #1: Measure Room Volume

Calculate the volume of the room in cubic feet by multiplying its length, width, and ceiling height (L x W x H).

Step #2: Determine Airflow Rate

Find the airflow rate of your ventilation system, usually measured in cubic feet per minute (CFM). This is the amount of air supplied or exhausted by the HVAC system.

Step #3: Input Data

Enter the room volume and airflow rate into the calculator.

Step #4: Calculate ACH

The calculator will provide the ACH, indicating the air change rate per hour.

ACH Calculation Example

Next, let’s walk through each step of calculating the ACH of a room. For this example, we’ll calculate the ACH of a living room with the following specifications:

Room length: 12 ft. Room width: 14 ft. Ceiling height: 10 ft. CFM: 168

  1. Calculate the area of the room in square feet: 12 x 14 = 168 square feet

  2. Calculate the room volume by multiplying square feet by room height: 168 x 10 = 1,680 cubic feet

  3. To calculate the value for the air exchange per hour, multiply the CFM of your device by 60: 168 x 60 = 10,080

  4. Divide the adjusted CFM value by the room volume: 10,080 / 1,680 = 6 ACH

Understanding ACH Results

The result of this calculation gives you the number of times the entire volume of air within the room is exchanged with fresh air in one hour. ACH directly affects indoor air quality by removing dust, contaminants, and air pollutants from room air. Rooms with a sufficient ACH reduce the need for air purifiers, exhaust fans, air filtration, or ventilation systems.

  • A higher ACH indicates more frequent air replacement, which can be crucial in areas requiring stringent air quality control. A higher ACH generally indicates better ventilation and air quality.

  • A lower ACH might be sufficient for less critical environments but could be inadequate for spaces requiring high air quality standards.

Our ACH Calculator can be used in conjunction with the ServiceTitan CFM Calculator to calculate the proper airflow rate for every room.

How to Adjust and Improve ACH

  • If ACH is lower than required, consider increasing ventilation by allowing more fresh air in from outdoors or using additional air purification methods.

If ACH is higher than needed, you might be able to reduce energy costs by adjusting ventilation without compromising air quality.

Benefits of Using Our ACH Calculator

  • Optimize ventilation: Helps HVAC techs know how to design and adjust ventilation systems for optimal air quality.

  • Health and safety compliance: Assists in meeting health and safety standards for air quality in various types of buildings.

Energy efficiency: Enables adjustments to ventilation for energy savings while maintaining air quality standards.

Frequently Asked Questions

The ideal ACH varies based on factors such as the building's purpose, occupancy, and ventilation requirements. Hospitals often require higher ACH (around 6-12), while residential spaces may require lower ACH (about 2-4).

Higher ACH rates can improve indoor air quality by reducing pollutants, particulate matter, and contaminants, and ensuring a constant supply of fresh air.

Yes, areas like laboratories, kitchens, and hospitals usually require higher ACH to ensure safety, control infection, and reduce exposure to hazardous materials.

Properly managed ACH can balance air quality with energy efficiency, reducing unnecessary ventilation while maintaining a healthy environment.