# How do I calculate air changes per hour?

The rate of air change per hour is calculated by using the formula ACH = 60 x CFM/V. In SI units, the calculation formula is expressed as n = 3600 x Q/V, according to the Engineering ToolBox.

CFM denotes the cubic feet per minute rating of a fan and is found in a fans manual, specification sheet or literature. Since CFM is expressed in minutes rather than hours, it is converted into cubic feet per hour by multiplying the CFM value with 60. Airflow in physics is denoted as Q, and when it is expressed in cubic meters or cubic feet per second, it needs to be multiplied by 3,600.

V denotes the volume of the room in cubic feet or cubic meters and is determined by using a measuring tape. The length, width and height of the room are measured in feet or meters and then multiplied by each other to get the volume.

The term air changes per hour, also abbreviated as ACH or ac/hr, is obtained by dividing airflow per hour with the volume of the room. It is used to describe the number of times air in the room is completely changed within one hour. It is a measure used in ventilation planning and air purifier ratings.

Q&A Related to "How do I calculate air changes per hour?"
 1. Measure the length, width and height of your room. 2. Multiply the length times the width times the height to calculate the volume of the room. For example, if your room is 10 http://www.ehow.com/how_5984401_calculate-air-chan...
 The calculation involves finding the distance in which someone has been traveling and determining how long it has taken for the destination to be reached in time. http://www.ask.com/web-answers/Reference/Other/how...
 The air entering the room should be the same as the air leaving the room, unless you are excluding "recycled' air. I believe you disregard whether the air is recycled or not, http://answers.yahoo.com/question/index?qid=200811...