1() they do not fit very well! I need 20X25x4" and that is what I ordred. The real size was at lest 1/2 inch smaller! This WILL allow a substantial amount of unfiltered air to enter the furnace. 2) Brand was tested and found their rating is way off. They do not filter as they shou;ld Bottom line, buying these CHEAp filters are not only bad foryour furance but also your health. PYRE RUBBISH! Oh yes if you return them you get tp pay the shipping!!!!