The 2428WFC MERV8 is manufactured CUSTOM for WaterFurnace and is considered to be the OEM replacement 1" MERV 8 air filter for their Geothermal Comfort Systems that use a 24 x 28 x 1 pre-filter.
The replacement filters used with WaterFurnace units that use a 24 x 28 x 1 pre-filter must use a filter that is a full 24" x 28". If you use a smaller filter sold by other manufacturers, your filter will not seal properly and you could get unfiltered air leaking around the edge of the filter, this is called bypass. The 2428WFC MERV 8 air filter is approximately 24" x 28" x 1" .
This package ships with 12 filters - and are Custom non-returnable once ordered.