What is the Optimum Air Velocity for Removing Grease Laden Air from a Kitchen Grease Exhaust System?

Neglected Grease Filter Picture

Why is the fan sucking my grease filters up into the hood?  Here are some possibilities

1.  Your fan may be turning too fast.  The ASHRAE research report RP-1033 shows that air movement a 500 fpm is more efficient and preferable to 1,000 fpm, 1,500 fpm and 2,000 fpm for removal of grease laden air from the sides of duct work.      A.  Fans turn too fast when the pullies are the wrong size.      B.  Motors come in 2 speeds, 1725 RPM and 3450 RPM.  Make sure you have the right motor and that it is wired correctly. 2.  You may need heavier filters.  Aluminum filters are considerably lighter than galvanized metal or stainless steel filters.  Simply changing your filters may correct this problem. 3.  Your filters may be clogged as shown in the photograph above.  The air passage through these baffle filters is restricted due to built up grease deposits.  Sometimes neglect prevents this area from being thoroughly cleaned without damage to the filters themselves and filter replacement is required.