Sears does not make furnaces or any other HVAC item. Sears buys the furnaces etc off some manufacturer (Usually the cheapest)and has there name (sears) and other paperwork attached to the unit fooling the general public into thinking that Sears actually manufactured the unit. As to when Sears started to make that furnace it was never made by Sears. As for Sears starting to sell that model number to the unsuspecting general public?? That is a good question and you might be given some type of a date at the sears part site/customer care.