The Z-Line 500AB *(Air Bear?),700SG *(Aprilaire?), 400HW*(Honeywell F-100?) and HWRSeries *(Honeywell FC40R?) arereplacement options that requireno modification to the existinghousing. All are rigidly constructedutilizing high quality MERV 8 orMERV 11 rated filtration mediabacked with a metal mesh to preventsagging during operation