How to Calculate CFM in HVAC
People have questions that they are buying the right HVAC system. Is it going to fit correctly? Here the role of CFM comes in.
HVAC technicians measure airflow using cubic feet per minute or a CFM calculator. It is to match the size of an HVAC system to the space or building. If it requires 1200 CFM, then a 3-ton HVAC system is good. Take the support of a leading HVAC company in India.
- What is CFM?
CFM, or Cubic Feet per Minute, is a unit for airflow calculation in HVAC. The contractors calculate CFM for a room for air purifiers, fans, and such.
- Why do we need to calculate CFM?
CFM is important to measure the amount of airflow a particular room needs. It tells how much quantity of an airflow device will spread per minute. In a big room, a small system will not work. It cannot provide the right amount of heating or cooling. There is a waste of energy if the system is overpowered. This is because it involves short cycling.
Hence, it is important to know how to calculate CFM. Large rooms require high CFM as there is more air circulation. Right HVAC system for your space, you need accurate CFM estimates.
- CFM Calculator: How To Calculate CFM? (CFM Calculation + Charts)
If you want to know how to calculate cfm in HVAC, here are the two methods.
In the first method, you need to calculate the airflow requirements of the space. It is based on the frequency and size of the room where the air will spread. Another method is calculating the capacity of the system based on its power. It is measured in the form of tons.
Let us find out about both in detail:
Calculating Ventilation Requirements for a Room
The frequency of change in the air per hour is different in different rooms. For example, a room having dangerous fumes need a frequent air change system. A kitchen needs a system that can change the air every three minutes.
Hence, here the CFM calculation involves the below formula:
Required airflow in CFM= total volume of the space / the air exchange interval
Room’s Volume= length multiplied by height and width and measured in feet.
For example, take a rectangular kitchen with an 8-foot ceiling, a room width of 10 feet, and a length of 20 feet.
The volume of the room comes out to be 1,600 cubic feet. If the air exchange interval is three minutes, the CFM comes out as 533 CFM (1600/3).
Calculation Based on System Output
CFM per square foot leads to the measurement of the airflow capacity of an HVAC unit. It helps identify whether the unit is big enough for the ducts and the space.
Here first need to find how much output there is per unit in tons.
1 ton = 12,000 British thermal units (BTUs)
An average output of an HVAC unit is 400.
Let us calculate this for a 10-ton HVAC unit. It serves a 2,000-square-foot building.
Airflow will be 10 tons x 400/2,000 = 2 CFM per square foot.
If the kitchen is 100 square feet, 400 CFM airflow is enough. This would not be enough for a 400 square feet kitchen.
CFM Calculation:
For example, there is a 300-square-foot bedroom. If you need to convert all air two times per hour/ every 30 minutes, how much CFM is required for such a room?
Here is the calculation.
Room Volume= 300 sq ft x 8 ft = 2,400 ft3.
To make it two times per hour (ACH = 2), we need to deliver 4,800 ft3 per hour. CFM is an ‘ft3 per minute unit. Hence, if you divide the total volume by 60, you will get 80 CFM.
Connect with industrial blower manufacturers if you want a blower with the right CFM.
- CFM Airflow Calculator
Input the area of room/space, ceiling height, and air changes per hour. The calculator will give the required CFM as an answer.
Total Area (Sq Ft):*
Ceiling Height (In Ft):*
Wanted Air Changes Per Hours (ACH):*
Calculated airflow (CFM):
- CFM Calculator How To Calculate CFM For A Room? (Solved Example)
For example, there is a 1,000 sq ft room with a ceiling of 8 ft height. Let us calculate the CFM of a fan exchanging all the air in such a room every 15 minutes (ACH = 4).
There are two ways to calculate fan CFM:
- Use the CFM formula.
- Use the room CFM airflow calculator above.
First method:
Total Area (Sq Ft): 1000
Ceiling Height (In Ft): 8
Wanted Air Changes Per Hours (ACH):4
Calculated airflow (CFM): 533
Second Method:
CFM = (Area x Height x ACH) / 60
Add the figures.
CFM = (1,000 sq ft * 8 ft * 4) / 60 min = 533 ft3/min = 533 CFM
- CFM Chart For Common Room Sizes
With the help of the CFM calculator, it is easy to calculate the airflow of various rooms. To help you out, here is an HVAC CFM chart mentioning the CFM for most common room sizes:
| Room Size: | CFM (At 2 ACH) |
| CFM for a 100 sq ft room | 27 CFM |
| CFM for a 200 sq ft room | 53 CFM |
| CFM for a 300 sq ft room | 80 CFM |
| CFM for a 400 sq ft room | 107 CFM |
| CFM for a 500 sq ft room | 133 CFM |
| CFM for a 600 sq ft room | 160 CFM |
| CFM for a 700 sq ft room | 187 CFM |
| CFM for a 800 sq ft room | 213 CFM |
| CFM for a 900 sq ft room | 240 CFM |
| CFM for a 1000 sq ft home | 267 CFM |
| CFM for a 1500 sq ft home | 400 CFM |
| CFM for a 2000 sq ft house | 533 CFM |
| CFM for a 2500 sq ft house | 667 CFM |
- How Many CFM Per Square Foot?
It is quite a common question. It is related to the ceiling height and ACH. If we take an 8 ft ceiling height, below is the CFM per sq ft for different values of ACH:
0.13 CFM per square foot at ACH = 1.
0.27 CFM per square foot at ACH = 2.
0.40 CFM per square foot at ACH = 3.
0.53 CFM per square foot at ACH = 4.
0.67 CFM per square foot at ACH = 5.
- Duct Diameter CFM Chart
For those using hvac duct CFM calculator, you also need to know the duct diameter to achieve the airflow.
Example: For a 300 CFM airflow, one needs a 10-inch flex duct diameter.
For the right ductwork size, check the below CFM sizing chart:
| Flex Duct Diameter: | CFM (Airflow) |
| 4-inch | 20 CFM |
| 5-inch | 50 CFM |
| 6-inch | 80 CFM |
| 7-inch | 120 CFM |
| 8-inch | 170 CFM |
| 9-inch | 230 CFM |
| 10-inch | 300 CFM |
| 12-inch | 500 CFM |
| 14-inch | 740 CFM |
| 16-inch | 1050 CFM |
| 18-inch | 1400 CFM |
| 20-inch | 1875 CFM |
- Airflow Units Like L/Min Or Cubic Meters Per Hour
CFM, mainly applied in the US, is an imperial unit. If you are using other units, such as l/min or m3/h, below is the formula to convert those units into CFM.
1 CFM = 1.699 m3/h
1 CFM = 28.317 l/minute
Conclusion
The professionals consider many factors while determining the right HVAC system for the room. CFM airflow calculator template is useful in providing the right recommendations. Connect with Envigaurd hvac contracting service near you if you are looking to install an HVAC system in your esteemed industry or business infrastructure.
FAQ
- How many CFM is a 1-ton unit?
It is 400 CFM.
- How to calculate the cfm of the blower?
You can use the formula:
CFM = (fpm * area), where fpm is the feet per minute.
At the place of the FPM value, input the area after it is squared. You will get the result.
- how to calculate cfm required for a machine
CFM = Machine Volume in Cubic Feet x Standard Pressure during a cycle x Cranks per Minute
- how do we figure cfm for the exhaust fan
For a standard 10ft by 10 ft room with an 8 ft ceiling, you will need an exhaust fan of 106.67 CFM. Formula is
Cubic Volume/7.5= CFM Necessary
(10ft * 10ft* 8ft)/7.5 = 106.67 CFM
- how to calculate blower capacity
Blower capacity required = 𝛑 r^2 x Vs