If you need building ventilation consulting or testing discussed in this article, call us at 973-366-4660 or e-mail us at info@atlenv.com for details and a free estimate.
Written By: Robert E. Sheriff, MS, CIH, CSP, President
March 18, 2020; Updated November 2021
Atlantic Environmental Inc. has 42+ years of experience in evaluating Industrial Ventilation Systems. Industrial facilities seldom, if ever, have all the roof vents, wall vents, exhaust fans, and local exhaust ventilation systems installed at the same time. This is even more true for the make-up air system. It is almost universal that the facilities or engineering departments have no idea how much air is moving through the building. When it is difficult to open the doors because of the strong negative pressure in the building (too much exhaust and lack of make-up air), it confirms that the system is not operating the way it should.
The many types of industrial facilities have different air changes per hour (ACH) depending on the activities taking place. This rate of ACH is dependent on the volume of air exhaust from general ventilation (wall fans, roof fans, etc.) and local exhaust systems (intended to remove air contaminants from the air before they get into the building air.) It is also dependent on the amount of make-up air supplied to the building.
Atlantic Environmental can measure the volume of air exhausted from all equipment (general ventilation and local exhaust ventilation) and measure the make-up air to determine if the total air supply and exhaust are capable of moving enough air for temperature, general air quality, and local contaminant control exhaust ventilation.
The following is a good reference table for some of the more common building uses and the ACH for those uses. The following list comes from “the Engineering Toolbox website at www.engineeringtoolbox.com and is a reasonable reference for ACH’s.
| Building/Room | Air Change Rate in ACH |
| All Areas in General | 4 |
| Auditorium | 8 – 15 |
| Bakeries | 20 – 30 |
| Beauty Shops | 6 – 10 |
| Boiler Rooms | 15 – 20 |
| Classrooms | 6 – 20 |
| Computer Rooms | 15 – 20 |
| Dental Centers | 8 – 12 |
| Garages –Repair | 20 – 30 |
| Hospital Rooms | 4 – 6 |
| Kitchens | 15 – 60 |
| Machine Shops | 6 – 12 |
| Malls | 6 – 10 |
| Municipal Buildings | 4 – 10 |
| Police Stations | 4 – 10 |
| Precision Manufacturing | 10 – 50 |
| Shops, Paint | 15 – 20 |
| Wood Shops | 5 |
| Theatres | 8 – 15 |
| Warehouses | 6 – 30 |
| Waiting Rooms, Public | 4 |
Please note that the above list identifies ACH rates without special consideration for industrial/commercial processes that may introduce air contaminants into the air that should be using local exhaust ventilation.
Measuring the ACH
There are two methods of determining the ACH rates in a building. The first, and most obvious is to actually measure the actual air flows.
The second method is to introduce a tracer gas into the air and measure its decline over time to determine the ACH.
Actual Measurement of Air Flows
Using a velometer, thermometer or vane anemometer, airflow measurements should be taken at all the exhaust and air supply points. These include all the local exhausts that may be used to control specific operations. Then the calculation of ACH is simple.
ACH = total air supply rate (feet/minute) x 60 minutes
The volume of space (ft³)
or ACH = total air exhaust rate (feet/minute) x 60 minutes
The volume of space (ft³)
As Industrial Ventilation Measurement Specialists, our primary service areas for Measurement and Consulting are New Jersey NJ, New York NY, (New York City), Pennsylvania PA, Connecticut CT, Delaware DE, Massachusetts, (Boston) MA, Rhode Island RI, Washington DC, Wisconsin WI, Maryland MD, Michigan MI, Illinois (Chicago) IL, Virginia VA, Indiana IN, Georgia (Atlanta) GA, Alabama AL, North Carolina NC, South Carolina SC, Tennessee TN, Texas (Dallas, Ft Worth) TX, Oklahoma OK, DC, Arkansas AR, Florida FL. We can service most other areas of the U.S. but additional travel charges will be applied.
As mentioned earlier, local exhaust building ventilation is the more appropriate method of capturing emissions from a particular process before it can get into the workroom’s air. The best reference for this approach is the ACGIH Publication, “Industrial Ventilation—A Manual of Recommended Practice,” 30th edition, a two-volume set.
The method of using a tracer gas to measure air changes per hour (ACH) is covered in other articles related to building ventilation on our website. Also under Ventilation.
If you are in need of building ventilation consulting or testing discussed in this article, call us at 973-366-4660, e-mail us at info@atlenv.com, or use our online form to get more information and a free estimate. We are professional Industrial Ventilation Measurement Specialists who are ready to help you.