Lennox Healthy Climate HCXF14 MERV 10 expandable-type replacement furnace filter - X8311. Filter dimensions: 20" x 20" x 5". Note: this item DOES NOT come with the replacement inner housing reusable filter frame. If you need to convert from a standard box-type media filter, purchase the Lennox X8305 filter kit which includes the expandable filter and the inner housing reusable filter frame. If you need a standard box-type 20" x 20" x 5" filter, purchase the Lennox X0585.