When it comes to heating, ventilation, and air conditioning (HVAC) systems, the right air filter size is essential for efficient operation and clean air. The recommended minimum filter area is 2.50 cubic feet per minute (cfm) per square inch of filter area, with a maximum speed of 300 feet per minute (fpm) for disposable filters. To calculate the right size for your system, follow these steps:Step 1: Measure the length and width (L x W) of the filter. If it's not square, use the smallest measurement first. Step 2: Use a basic formula of 2 CFM of airflow per square inch of disposable air filter.
Compare this size to the required number of square feet determined in step one to determine how many filters you need. Step 3: Choose the appropriate pore size of the final filter to retain the smallest microorganism to be removed. Step 4: Measure the pressure drop of the new filter after replacing the old one to ensure it works as intended. Filter pressure drop tests allow a technician to effectively evaluate the type of filter needed to fit the system. Since two filters are needed to obtain an adequate filter surface area, they should be installed in a V-type installation or multiple filter grids. Millipore has developed a constant flow sizing technique, Pmax, that can be used to select and size depth filters. Be sure to change your air filters every 30 to 90 days, depending on the type and efficiency of the filter. If the filter pressure drop is extremely low, look for signs of filter bypass or a poorly constructed filter grid assembly.