If the area surrounding your filter isn't completely sealed, air can be

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filter housing slot, or refer to your furnace instructions manual for more information Measure furnace and ac filter Measure HVAC filter housing Measure

Our Furnace Filter Magnetic Slot Seal is the answer to this question Our air-sealed cover has been specifically designed to eliminate energy loss and stop Your filter should be a bit smaller on each side of the filter housing slot, thus allowing you to slide the filter in with ease Most AC and

linear slot diffuser with plenum box Furnace Filter Slot Cover [Easy fix to HVAC Air Leak with One Hour Heating and Air If your filter slot on your furnace is exposed, dust and dirt can bypass your filter and go