I need to replace normal 2" pleated filters,Merv 7 or 8, with Merv 14 pleated. The cost between Merv 13 and 14 is substantial, any one know what difference there is between the 13 & 14? Also, in one of the AHU's, I have 12" Pleated Box Filters" and 2" pre-filters, does anyone know if I can add the 12" Merv rating to the normal 2" pleated {7 or 8 merv} and achieve my 14 Merv? Thanks.