HEPA filters only need replacing when restricted (clogged), dark color may be an indication of a sooty environment where frequent filter changes would be wise. FLT4825, True-HEPA Replacement Filter for AC4800 Series (Filter B), $27, is projected to last 6 to 8 months. ...
REPLACEMENTS Replace the filter every 3 to 4 months and the UV-C bulb every 10 to 12 months; Filters: Germ Guardian filter Q 4-Pack (Model FLT200); UV C Bulb (Model LB200) GENUINE REPLACEMENTS Only use Genuine GermGuardian replacement parts to maintain performance View more...