These MERV 8 replacement filters are for use with Friedrich FreshAire Series PTACs. They are packaged in a 10 pack. Each Friedrich FreshAire PTAC requires only 1 MERV 8 filter. This 10 pack can be used to replace the MERV 8 Filters in 10 FreshAire PTAC units. Filters should be changed fairly frequently but this also depends on the climate and frequency of use of the PTAC. Filters should at least be checked twice a month. Dirty filters affect the efficiency of your PTAC unit.