Flow Rate: — CFM
Air Filter Flow Rate Calculator
Understanding the airflow through an HVAC system is crucial for its efficient operation and for maintaining good indoor air quality. The flow rate of an air filter, often measured in Cubic Feet per Minute (CFM), indicates the volume of air that passes through the filter over a one-minute period. This calculation is fundamental in selecting the correct filter size and type for a given application, ensuring optimal performance without overworking the fan motor.
How to Calculate Air Filter Flow Rate
The flow rate (Q) of air through a filter can be calculated using a simple formula derived from the principles of fluid dynamics. It directly relates the speed at which air moves (velocity) to the surface area it passes through. The formula is:
Q = V × A
Where:
- Q is the volumetric flow rate (in CFM – Cubic Feet per Minute).
- V is the average velocity of the air passing through the filter (in FPM – Feet Per Minute).
- A is the face area of the filter (in sq ft – Square Feet).
To use this calculator, you need to know two key pieces of information about your air filter and HVAC system:
- Air Velocity (FPM): This is the speed at which the air is moving. In HVAC, a common target velocity for filters is around 500 FPM to balance efficiency and resistance. You can often find this information in your HVAC system's specifications or by using a specialized airflow meter.
- Filter Face Area (sq ft): This is the total surface area of the filter that air passes through. It's typically calculated by multiplying the filter's width by its height. For example, a 20″ x 20″ filter (which is 1.67 ft x 1.67 ft) has a face area of approximately 2.78 sq ft (1.67 * 1.67).
By inputting these values into the calculator, you can easily determine the CFM rating of your filter, which is essential for ensuring your HVAC system operates efficiently and effectively.
Example Calculation
Let's say you have an air filter with a face area of 20 square feet and your HVAC system is designed to move air through it at a velocity of 500 feet per minute.
Using the formula Q = V × A:
Flow Rate (Q) = 500 FPM × 20 sq ft = 10,000 CFM
This means the filter is capable of handling 10,000 cubic feet of air per minute. It's important to match this flow rate to the requirements of your HVAC unit to prevent strain and ensure proper air filtration.