I live in a highly energy efficient house with an Mini-Split HVAC system. I use the filter for my air intake /make-up air opening in the ceiling. The Filtrete filter is the only one I have found that accurately fits the duct opening. Other makes I have tried  are slightly smaller than the stated 12 x 12 size which means they allow unfiltered air to enter the house through the gaps around the filter. An additional annoyance is that the filter falls out of the opening when I open the hinged cover.