What Are the ACH Values of a Typical Room?

Air Changes per Hour (APH) contributes to the comfort of a room.

Air Changes per Hour (ACH) represents the number of times the total volume of air in a space is either purified or replaced with fresh air. A number of factors, including room geometry, affect the values used in ACH.

Definition

The Environmental Protection Agency has determined that indoor air is up to 100 times more polluted than outside air. ACH is the major influence upon the purification of indoor air. ACH is calculated by determining the cubic feet per minute (CFM) of air that a filtering system can handle and multiplying it by 60.

Residential ACH Values

The Home Ventilating Institute recommends levels of 8 ACH for bathrooms, 15 ACH for kitchens, and 6 ACH for other rooms. You can plot the performance of ventilating fans on a graph which is based upon static pressure for the air ducts and values for sections of duct, elbows and termination devices. The chart will help you find ventilation fans that are able to push the necessary volume of air out of the building.

Importance of ACH

The average person breathes 16,000 quarts of air per day, and there are approximately 70,000 particles in each quart of air. This represents an intake of more than a billion particles per day per person. The exchange of polluted air with fresh or filtered air is vital to our health. ACH represents this exchange.

References

• Touch Briefings: Frequency of Air Changes per Hour
• GreenR: How to Size Ventilation Fans

Resources

• The Engineering Toolbox: Air Change Rates for Typical Rooms and Buildings