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CFM Calculator

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Room air change per hour requirementsWhat is CFM? How to calculate CFM for a room?Air change per hour formulaHow to use our CFM calculatorSample on how to calculate airflow in CFMWant to learn more?FAQs

This CFM calculator will help you determine the required air flow rate in CFM units for any room square footage and air change per hours, or ACH. But what does CFM stand for? In the article, we explain the CFM meaning, together with a computational example. Our tool also works as an air changes per hour calculator when used in reverse.

With this calculator, you will also learn how to estimate airflow in CFM (cubic feet per minute), how to calculate CFM for a room of any floor area and ceiling height, and how to calculate air changes per hour. You can also learn how we can use the formula for CFM airflow to get the air changes per hour formula. Keep on reading to start learning.

Room air change per hour requirements

In any building, there will be a variety of rooms with various functions and purposes. We commonly find a living room, bedroom, dining area, kitchen, and bathroom in a basic house. In most workplaces, we usually have a lobby or receiving area, hallways, function rooms, offices, restrooms, and so much more. Each room has a specific purpose, and we stay in each room for different amounts of time during the day.

Depending on the activities we do in a room, the ventilation required to maintain a fresh air flow will change. Having adequate ventilation and airflow in a room is essential for breathing and for some appliances and equipment to work properly.

Aside from that, with correct ventilation, we can control the humidity and temperature in a room and quickly remove any odors, fumes, and even particles that might linger, like in the kitchen or living room.

In order to remove these air pollutants, we have to change the air in the room by introducing new volumes of air. Depending on the room, we might need to perform multiple air changes per hour to achieve our desired air quality in that room. Here are some of the typical values of recommended air changes per hour for some of the most common types of rooms:

Building/Room

Air Changes per Hour (ACH)

Residential

Basements

3-4

Bedrooms

5-6

Bathrooms

6-7

Living rooms

6-8

Kitchens

7-8

Laundry room

8-9

Non-residential

Offices

Business offices

6-8

Canteens

7-12

Conference rooms

8-12

Medical procedure offices

9-10

Copy rooms

10-12

Main computer rooms

10-14

Smoking area

13-15

Restaurants

Dining area

8-10

Food staging

10-12

Kitchens

14-60

Bars

15-20

Public places

Hallways

3-5

Waiting rooms

4-8

Banks

4-8

Hospital wards

6-8

Gymnasiums

6-10

Malls and retail stores

6-10

Lavatories

6-15

Classrooms

6-20

Foyers

8-10

Churches

8-12

Theatres and auditoriums

8-15

Restrooms

10-12

Swimming pools

10-15

Hospital facilities

10-20

Auditoriums

12-14

Smoking rooms

15-20

We consider one air change per hour or 1 ACH to occur when an entire room's air volume is replaced once with new air within an hour. As an example, a 30 m³ room that requires four air changes per hour would need 30 m³ × 4 = 120 m³ of air to flow in it within an hour.

Calculating the airflow requirements for a room will help us decide what actions to take to provide quality air in any room. Also, choosing the right appliances for our home often leads to lower electric bills. In the next sections, let's learn about CFM meaning and discover how to calculate airflow in the CFM unit, which is the mostly-used unit of measure used for airflow.

🙋 Do you know the relative humidity and temperature are related to the dew point temperature? Check our dew point calculator to learn more.

What is CFM? How to calculate CFM for a room?

CFM, or cubic feet per minute, is a unit of measure used for volume flow (usually for fans). To calculate CFM, we have to determine the volume of any room in cubic feet, multiply it by its recommended ACH, and divide everything by 60 minutes per hour. Below is the formula for CFM airflow:

airflow = room's floor area × ceiling height (ft) × ACH / 60

where:

  • airflow — Required air volume flow rate across the room in the CFM unit;
  • room's floor area — The room's floor square footage;
  • ceiling height — The room's average height from floor to ceiling in feet; and
  • ACHAir change per hour required for the given room.

Air change per hour formula

As you already know what CFM means, you shouldn't have any problems evaluating its corresponding parameter, ACH.

If you need to determine the air change rate of a room, provided that you know its volume and airflow, we can rearrange the formula for CFM airflow to derive the ACH formula, as expressed below:

ACH = 60 × airflow / room's volume

Please note that the room's volume must also be in cubic feet and the airflow is also in cubic feet per minute.

You can use our volume converter if you ever have the room's volume in different units.

How to use our CFM calculator

Using our CFM calculator is very easy and straightforward. All you have to do is:

  1. Input the room's dimensions (length and width for a rectangular one).

  2. If you know the room's floor area that you are considering, you can instead enter that value in the calculator, together with the ceiling height.

  3. From the air change per hour table, choose your desired ACH to input in our calculator.

  4. The calculator will instantly provide you with the airflow in CFM and other units.

To use our CFM calculator as air changes per hour calculator, simply input the airflow first and then the room dimensions. As a result, you obtain the value for the air changes per hour.

Sample on how to calculate airflow in CFM

Let's say we want to install a ventilation system that would provide 8 ACH to a 250 ft² home kitchen with a ceiling height of 8 ft. Using the formula for CFM airflow, we can estimate the required CFM for the kitchen, as shown below:

airflow (CFM) = floor area × ceiling height × ACH / 60

airflow = 250 ft³ × 8 ft × 8 ACH / 60

airflow = 2000 ft³ × 8 ACH / 60

airflow = 266.6666 CFM ≈ 266.67 CFM

We now know that we have to install a ventilation system that could generate roughly 270 CFM for the said kitchen from the calculation above. If we plan on building an energy-efficient house with a centralized ventilation system, it would be best to work out the CFM requirement for each room. This way, we can tell if we would need a robust ventilation system to supply adequate airflow to each room.

Want to learn more?

If you found our CFM calculator useful, you might also find our air conditioner room size calculator interesting, especially if you are also considering installing an air conditioner in your house.

FAQs

How do I calculate CFM?

To calculate the CFM or airflow of a room, please follow the steps below:

  1. Multiply the room's floor area by the ceiling height to obtain the volume.
  2. Multiply the volume by the recommended air change per hour (ACH) of the room.
  3. Finally, divide the result from step 2 by 60.
  4. The result is the airflow of the room in CFM (cubic feet per minute).

How much CFM do I need for 2000 square feet home?

The needed airflow of a 2000 ft² home is 1866.7 CFM, assuming the ceiling height is 14 ft, which makes the volume 28,000 ft³.

How much CFM is good airflow?

Generally speaking, the higher the CFM, the better. If the room is under 200 ft², a good airflow value would be 2000 to 3000 CFM. But keep in mind that the CFM requirements vary with the size of the space and the purpose of the airflow.

For instance, a residential bathroom should have an exhaust fan with an airflow of 50 CFM, whereas for a kitchen hood (depending on the size), 100-300 CFM airflow is considered good.

What is the formula to calculate CFM?

The formula to determine the CFM of airflow is easy to apply.

Airflow (CFM) = Room's floor area × Ceiling height (ft) × ACH / 60

where:

  • ACH — Air change per hour.

The unit of airflow is CFM, which means cubic feet per minute.

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