The filter inside the furnace was completely packed with dirt, and the furnace had overheated, yet dozens of clean filters were scattered throughout the basement. When I told the customer what had happened she said "No way! We change our filters every month! On the 1st day of every month and my husband changes them." I said "Ma'am, have you been in the basement lately?" When I showed her the piles of clean filters... she said something I can't repeat.