Air changes per hour
Air changes per hour is a measure of how many times the air within a defined space (normally a room or house) is replaced.
The actual percentage of an enclosure's air which is exchanged in a period depends on the airflow efficiency of the enclosure and the methods used to ventilate it. The actual amount of air changed in a well mixed ventilation scenario will be 63.2% after 1 hour and 1 ACH.  In order to achieve equilibrium pressure, the amount of air leaving the space and entering the space must be the same.
ACH equation in Imperial units
- N = number of air changes per hour
- Q = Volumetric flow rate of air in cubic feet per minute (cfm)
- Vol = Space volume L × W × H, in cubic feet
Air change rate 
|This table does not cite any references or sources. (February 2013)|
|Commercial kitchens & Toilets||15–30|
- Bearg, David W. (1993). Indoor Air Quality and HVAC Systems. CRC Press. p. 64. ISBN 0-87371-574-8.
- "International Passive House Association - Guidelines" (in english). Retrieved 23 March 2013.
|This standards- or measurement-related article is a stub. You can help Wikipedia by expanding it.|