CFM, or cubic feet per minute, is an acronym that is used to measure how much airflow a particular room needs or how much an airflow device will exchange each minute. It is used in HVAC calculation. HVAC is an acronym which stands for heating, ventilation and air conditioning.
A room’s CFM is calculated to know how many cubic feet of air can be displaced or exchanged each minute. This means that a room having a volume of 1000 cubic ft will need components that have a total CFM of 1000.
The room’s volume is calculated by multiplying its height by length and then multiplying the total by width. But as we all know, not all rooms are strictly rectangular or square-shaped.
If a room is irregularly shaped, you can simply figure out what its actual shape is and measure the corresponding metrics of each wall area, and then calculate using a formula that is used to calculate the volume of that particular shape. For a much simpler approach, simply measure the area of a room and multiply it by the height of the said room to calculate the volume.
CFM calculator: How often should my room exchange air?
The figurative number for how often a room’s air should be exchanged depends solely on the person. Every constructor has a rough idea of CFM, and upon their calculation, they will tell a client how and what their space needs to have acceptable CFM.
Even though this number is specific to every room, here are a few rough speculations to help you:
- Kitchen, cafeteria, bakery, laboratory, bars- every 2-5 mins
Spaces where food is prepared or experiments are conducted need an adequate amount of airflow in order to prevent any sort of air restriction or suffocation. These spaces require moderate to high air circulation.
- Warehouses, go-downs, factories, machine shops- every 3-7 minutes
Spaces, where industrial work is conducted, need high amounts of circulation but also have a comparatively larger base area and volume. They are not as intensive as engine rooms or food spaces, but airflow is still crucial as these spaces typically have more extensive work done inside.
- Classrooms, office rooms, gymnasiums, restrooms- every 4-10 minutes
Homes and commercial spaces like restaurants or offices have less demanding airflow requirements. Airflow in these types of spaces is not particularly crucial but is still a crucial factor when it comes to residential spaces.
Also, it is important to know that many smaller units that conduct air flow or air conditioning are better than having one large unit that does all of the work. Smaller units exchange air faster and more efficiently.
CFM calculator: How to calculate CFM
Calculating the CFM of an enclosure is no rocket science and is a fairly easy task to do so. You can calculate the CFM of any enclosed space through the following steps:
- Calculate the volume of the room.
- Multiply the volume by the desired number of times you want to exchange air through it.
- Divide the total by 60. You can skip this step if you want to know how much airflow you need hourly.
FAQs
Does less CFM affect the quality of the air that is circulating inside an enclosure?
Having a CFM that is less than the required value for HVAC can provide uncomfortable working spaces for workers and, in some cases, can even prove to be hazardous.
Does the RPM of indoor equipment matter when calculating CFM?
The CFM of a certain space is heavily determined by airflow, which is determined by the number of rotations of any equipment, be it fans or air conditioners, in a minute.
