Use this ACH Calculator tool to find the total number of air changes per hour, or per minute, based on your room dimensions and CFM (Cubic Feet per Minute) of your filtration device. (ACH is also referred to as turnover time.)
Need a dental calculator to determine settle time? Check out our dental operatory settle time calculator tool here: Dental Operatory Settle Time Calculator
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ACH or ACPH stands for Air Changes per Hour and is commonly referred to as “air exchange rate” or “air change rate”. It is a measurement of how many times a volume of air within a room will be added, removed, or exchanged with filtered clean air
To calculate Air Changes Per Hour (ACH), find the CFM of your device and multiply that by 60 then divide that total by the total cubic feet of the room to get your total ACH. 
Q= CFM of filtration device
Vol= Room Volume
The formula to calculate ACH is 60 multiplied by the cfm of your air exchange device, divided by the volume of air in the room.
The ACH formula as an expression is: ACH=60Q/Vol
ACH = number of air changes per hour
Q = Volumetric flow rate of air in cubic feet per minute (cfm)
Vol = Space volume L x W x H, in cubic feet
To calculate the volume of air in a room multiple the length, width, and height to get your total cubic air volume.
The formula for air volume as an expression is: Vol = L x W x H
L = Length
W = Width
H = Height
CADR stands for Clean Air Delivery Rate. this measurement is used to show how much of the specific particles to be removed from the air. In other words, CADR rating indicates how fast the air purifier can clean the air within a particular size room.
CADR is used for home appliances and the rating system is tested and certified by the Association of Home Appliance Manufacturers.
Below you’ll find additional ACH requirements for specific types of healthcare related rooms.
Dental Room Air Changes Per Hour
| Area | Minimum total air changes per hour |
| Enclosed Dental Operatory | 12 |
| Open Dental Operatory | 6 |
| Cleanup/ Sterilization | 10 |
| Laboratory | 6 |
| Dark Room | 10 |
| General Dental Centers | 8-12 |
| Oral Surgery Room | 15 |
Air changes/hour (ACH) and time required for airborne-contaminant removal by efficiency
| ACH | Time (mins.) required for removal 99% efficiency |
Time (mins.) required for removal 99.9% efficiency |
| 2 | 138 | 207 |
| 4 | 69 | 104 |
| 6+ | 46 | 69 |
| 8 | 35 | 52 |
| 10+ | 28 | 41 |
| 12+ | 23 | 35 |
| 15+ | 18 | 28 |
| 20 | 14 | 21 |
| 50 | 6 | 8 |
Learn about the Pure Breeze HEPA Air Purifier and related HEPA air cleaning equipment here.
Related: Key Takeaways on How to Slow the Spread of COVID-19 by Clearing the Air
References