18x28x1 Exact MERV 12 Plus Carbon AC Furnace Filters 6 Pack Trimmers It also features our patented

It also features our patented Lock & Seal plug system design

the inner diameter at the bottom is going to be smaller

and propagating smaller cuttings

- Economical

18x28x1 Exact MERV 12 Plus Carbon AC Furnace Filters 6 Pack Trimmers It also features our patentedNordic Pure Custom MERV 12 Plus Carbon air filters are made based on the actual measurements so be sure to measure your current filter to get the EXACT dimensions before ordering. As with all Nordic Pure filters, the effective life of your filter depends on the environment in which you live. We recommend changing 1 and 2 filters every 30 90 days. Our 4, 5 and 6 inch thick filters could last up to 6 months. EXACT MEASUREMENT: Furnace and air condition