Q:
# How do I calculate air changes per hour?

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### Quick Answer

**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.

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Q:
## How do you calculate percent efficiency?

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Full Answer >**Percent efficiency is calculated by determining the actual output and then dividing by the maximum possible output.**The result is multiplied by 100 in order to move the decimal two places to the right.Filed Under: -
Q:
## How do you calculate the BTU of an air conditioner?

A:BTU is an abbreviation for British Thermal Unit, which is the international measure of energy. An air conditioner's BTU must be matched to the size of the room for adequate cooling. BTU tables estimate different energy requirements.

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Q:
## How do you calculate the proper air conditioner size for a house?

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Full Answer >**Measure the square footage of all the rooms in the home that will be cooled, and then compare that number to the government's recommended British thermal unit capacity list.**A 2,500-square-foot house requires 34,000 Btu.Filed Under: -
Q:
## What is the formula for calculating porosity?

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Full Answer >**Porosity is calculated is the ratio between the pore volume of a medium and its total volume, and it is expressed as n=Vv/Vt.**The Vv refers to the pore or void's volume, and it can have air (Va) and Water (Vw).Filed Under: