If you work in the HVAC industry, you know how important it is to properly size and design HVAC systems. One of the key elements of this process is calculating the required CFM (cubic feet per minute) for each space that will be served by the system. In this article, we will provide a comprehensive guide to HVAC CFM charts, including what they are, how to use them, and why they are so important for HVAC professionals.
What is an HVAC CFM Chart?
An HVAC CFM chart is a tool that is used to determine the required CFM for each space that will be served by an HVAC system. The chart takes into account a number of factors, including the size of the space, the number of people who will occupy the space, the amount of equipment that will be present, and the desired temperature and humidity levels.
How to Use an HVAC CFM Chart
Using an HVAC CFM chart is a relatively straightforward process. To get started, you will need to gather some basic information about the space that you are designing an HVAC system for. This may include the size of the space, the number of people who will be present, and any special requirements for temperature or humidity levels.
Once you have this information, you can consult an HVAC CFM chart to determine the required CFM for the space. Simply locate the appropriate row and column on the chart, and read the corresponding CFM value.
Why HVAC CFM Charts are Important
Properly sizing an HVAC system is critical to ensuring that it will operate efficiently and effectively. If a system is undersized, it may not be able to adequately heat or cool the space it serves, leading to discomfort for the occupants and potentially costly repairs. Conversely, if a system is oversized, it may be more expensive to install and operate than necessary, and may not effectively dehumidify the space.
By using an HVAC CFM chart, HVAC professionals can ensure that they are properly sizing their systems and avoiding these potential pitfalls.
CFM Sizing Chart For Flex Round Ducts (50-1,700 CFM)
| Duct Diameter (inches) | Air Flow (CFM) |
|---|---|
| 4 | 50 |
| 5 | 75 |
| 6 | 110 |
| 7 | 150 |
| 8 | 200 |
| 9 | 250 |
| 10 | 325 |
| 12 | 475 |
| 14 | 700 |
| 16 | 1,000 |
| 18 | 1,350 |
| 20 | 1,700 |
This chart can be used by HVAC professionals to select the appropriate flex round duct diameter for a given air flow requirement. For example, if the required air flow for a space is 300 CFM, a duct with a diameter of 10 inches would be suitable. It is important to note that this chart is just one example of a sizing chart and that other charts may be used for different types of ducts or different air flow ranges.
CFM Sizing Chart For Metal Round Ducts (50-2,000 CFM)
| Duct Diameter (inches) | Air Flow (CFM) |
|---|---|
| 4 | 50 |
| 5 | 75 |
| 6 | 110 |
| 7 | 150 |
| 8 | 200 |
| 9 | 250 |
| 10 | 325 |
| 12 | 500 |
| 14 | 700 |
| 16 | 1,000 |
| 18 | 1,350 |
| 20 | 1,700 |
| 24 | 2,500 |
| 30 | 4,000 |
| 36 | 5,500 |
| 42 | 7,000 |
| 48 | 8,500 |
| 60 | 13,000 |
| 72 | 18,000 |
This chart can be used by HVAC professionals to select the appropriate metal round duct diameter for a given air flow requirement. As with the flex round duct chart, it is important to note that other charts may be used for different types of ducts or air flow ranges, and that factors such as the shape of the duct and the type of material used can also affect the air flow. It is always best to consult with an HVAC professional to ensure proper sizing of ductwork for a particular project.
4-Inch Rectangular Ducts Size Chart (60-330 CFM)
| Duct Height (inches) | Duct Width (inches) | Air Flow (CFM) |
|---|---|---|
| 8 | 4 | 60 |
| 9 | 4 | 70 |
| 10 | 4 | 80 |
| 11 | 4 | 90 |
| 12 | 4 | 100 |
| 13 | 4 | 115 |
| 14 | 4 | 130 |
| 15 | 4 | 145 |
| 16 | 4 | 160 |
| 17 | 4 | 175 |
| 18 | 4 | 190 |
| 19 | 4 | 210 |
| 20 | 4 | 230 |
| 21 | 4 | 250 |
| 22 | 4 | 270 |
| 23 | 4 | 290 |
| 24 | 4 | 310 |
| 25 | 4 | 330 |
This chart can be used to select the appropriate 4-inch rectangular duct size for a given air flow requirement. As with other sizing charts, it is important to note that other factors can also affect air flow, such as the length of the duct, the number of bends and turns, and the type of material used. It is always best to consult with an HVAC professional to ensure proper sizing of ductwork for a particular project.
6-Inch Rectangular Ducts Size Chart (60-775 CFM)
| Duct Height (inches) | Duct Width (inches) | Air Flow (CFM) |
|---|---|---|
| 8 | 6 | 60 |
| 9 | 6 | 70 |
| 10 | 6 | 80 |
| 11 | 6 | 90 |
| 12 | 6 | 100 |
| 13 | 6 | 120 |
| 14 | 6 | 140 |
| 15 | 6 | 160 |
| 16 | 6 | 180 |
| 17 | 6 | 200 |
| 18 | 6 | 220 |
| 19 | 6 | 240 |
| 20 | 6 | 260 |
| 21 | 6 | 290 |
| 22 | 6 | 320 |
| 23 | 6 | 350 |
| 24 | 6 | 380 |
| 25 | 6 | 410 |
| 26 | 6 | 445 |
| 27 | 6 | 480 |
| 28 | 6 | 515 |
| 29 | 6 | 550 |
| 30 | 6 | 585 |
| 31 | 6 | 620 |
| 32 | 6 | 655 |
| 33 | 6 | 690 |
| 34 | 6 | 725 |
| 35 | 6 | 760 |
| 36 | 6 | 775 |
This chart can be used to select the appropriate 6-inch rectangular duct size for a given air flow requirement. As with other sizing charts, it is important to note that other factors can also affect air flow, such as the length of the duct, the number of bends and turns, and the type of material used. It is always best to consult with an HVAC professional to ensure proper sizing of ductwork for a particular project.
8-Inch Rectangular Ducts Size Chart (90-1,500 CFM)
| CFM | Width | Height | Velocity |
|---|---|---|---|
| 90 | 4 | 14 | 295 |
| 110 | 6 | 10 | 349 |
| 125 | 5 | 12 | 303 |
| 150 | 6 | 12 | 363 |
| 180 | 5 | 14 | 332 |
| 200 | 7 | 10 | 407 |
| 225 | 6 | 14 | 419 |
| 250 | 7 | 12 | 469 |
| 300 | 6 | 16 | 464 |
| 350 | 7 | 14 | 538 |
| 400 | 8 | 12 | 570 |
| 450 | 6 | 20 | 545 |
| 500 | 10 | 10 | 603 |
| 550 | 7 | 20 | 627 |
| 600 | 8 | 16 | 684 |
| 700 | 10 | 14 | 776 |
| 800 | 8 | 20 | 811 |
| 900 | 10 | 18 | 924 |
| 1000 | 12 | 14 | 963 |
| 1200 | 10 | 22 | 1124 |
| 1400 | 12 | 20 | 1306 |
| 1500 | 14 | 16 | 1306 |
This chart indicates the appropriate width and height for 8-inch rectangular ducts based on the required CFM. It also includes the recommended air velocity in feet per minute to achieve optimal airflow. When selecting the size of the duct, it is crucial to consider the amount of air that needs to be circulated in the system to ensure maximum efficiency and performance.
10-Inch Rectangular Ducts Size Chart (120-2,350 CFM)
| CFM | Width | Height | Velocity |
|---|---|---|---|
| 120 | 4 | 20 | 298 |
| 150 | 5 | 20 | 372 |
| 175 | 6 | 16 | 374 |
| 200 | 5 | 18 | 347 |
| 225 | 6 | 18 | 393 |
| 250 | 5 | 20 | 435 |
| 275 | 6 | 20 | 470 |
| 300 | 7 | 16 | 450 |
| 350 | 5 | 24 | 521 |
| 400 | 6 | 22 | 580 |
| 450 | 7 | 20 | 623 |
| 500 | 10 | 16 | 698 |
| 550 | 6 | 26 | 753 |
| 600 | 8 | 20 | 776 |
| 650 | 7 | 24 | 830 |
| 700 | 10 | 18 | 851 |
| 800 | 8 | 24 | 970 |
| 900 | 10 | 22 | 1096 |
| 1000 | 12 | 20 | 1205 |
| 1200 | 10 | 30 | 1447 |
| 1400 | 12 | 26 | 1693 |
| 1600 | 14 | 22 | 1807 |
| 1800 | 16 | 20 | 2016 |
| 2000 | 16 | 22 | 2234 |
This chart shows the recommended width and height for 10-inch rectangular ducts based on the required CFM. It also provides the suggested air velocity in feet per minute for optimal airflow. When choosing the size of the duct, it is crucial to consider the amount of air that needs to be circulated in the system to ensure maximum efficiency and performance.
12-Inch Rectangular Ducts Size Chart (150-3,050 CFM)
| Airflow (CFM) | Duct Size (inches) |
|---|---|
| 150 | 12×4 |
| 200 | 12×6 |
| 250 | 12×8 |
| 300 | 12×10 |
| 350 | 12×12 |
| 400 | 14×10 |
| 450 | 14×12 |
| 500 | 14×14 |
| 550 | 16×10 |
| 600 | 16×12 |
| 700 | 16×14 |
| 800 | 18×12 |
| 900 | 18×14 |
| 1,000 | 18×16 |
| 1,200 | 20×14 |
| 1,400 | 20×16 |
| 1,600 | 22×16 |
| 1,800 | 24×16 |
| 2,000 | 24×18 |
| 2,200 | 24×20 |
| 2,400 | 26×18 |
| 2,600 | 26×20 |
| 2,800 | 28×20 |
| 3,000 | 30×20 |
This chart shows that a 12-inch rectangular duct can handle airflow from 150 to 3,050 CFM depending on the size of the duct. As with the other charts, it is important to choose the right size of duct for the required airflow to ensure efficient and effective HVAC performance.
It is also important to note that these sizing charts are intended as guidelines and not as hard rules. There may be other factors to consider in sizing and designing an HVAC system, such as the layout and design of the building, the location of the system components, and the type of equipment being used. It is recommended to consult with a professional HVAC contractor or engineer to ensure a properly designed and installed system.
Factors that Affect HVAC CFM Requirements
There are a number of factors that can affect the required CFM for an HVAC system. Some of the most important factors to consider include:
- The size of the space
- The number of people who will occupy the space
- The amount of equipment that will be present in the space
- The desired temperature and humidity levels
- The climate in which the space is located
By taking these factors into account, HVAC professionals can ensure that they are accurately calculating the required CFM for each space they design an HVAC system for.
Common Mistakes to Avoid When Using an HVAC CFM Chart
While HVAC CFM charts are a useful tool, it is important to use them correctly to avoid making costly mistakes. Some common mistakes to avoid when using an HVAC CFM chart include:
- Failing to accurately measure the space
- Not taking into account the number of people who will occupy the space
- Overlooking the presence of equipment that will generate heat or require ventilation
- Failing to consider the desired temperature and humidity levels
- Not adjusting the required CFM based on the climate in which the space is located
By being aware of these potential pitfalls, HVAC professionals can ensure that they are using HVAC CFM charts correctly and avoiding costly mistakes.
Conclusion
In conclusion, HVAC CFM charts are a critical tool for HVAC professionals who want to properly size and design HVAC systems. By taking into account a number of important factors, such as the size of the space, the number of people who will occupy the space, and the desired temperature and humidity levels, HVAC professionals can ensure that they are accurately calculating the required CFM for each space they design an HVAC system for.
FAQ
What is the most important factor to consider when using an HVAC CFM chart?
The most important factor to consider is the size of the space. CFM requirements are directly related to the volume of air in the space that needs to be circulated.
Can I use the same HVAC CFM chart for every building?
No, each building has unique characteristics that affect the required CFM. It is essential to use a chart that takes into account the specific factors of the building being designed.
What happens if the HVAC system is undersized?
If the HVAC system is undersized, it will not be able to adequately cool or heat the space. This can result in uncomfortable indoor temperatures, decreased air quality, and increased energy costs.
Are HVAC CFM charts only used for new HVAC system installations?
No, HVAC CFM charts are also used in retrofit projects where an existing HVAC system is being replaced or modified.
Can I calculate the required CFM without using an HVAC CFM chart?
While it is possible to calculate the required CFM without using a chart, it is not recommended. HVAC CFM charts are designed to take into account all the necessary factors and provide accurate calculations, reducing the risk of errors in the design process.