We bought this 28 year old home which had a "secret smoker." We discovered this after the purchase and living in the home after the Minnesota cold weather and closed window weather began. We painted all walls and ceilings, recarpeted every carpeted room, put new flooring on all the others. Then it occurred to us to change to a better furnace/air conitioner fan filter. We could detect steady improvement with the use of a Filtrete #15. Today our home no longer has that smoked-in/stale odor, but it has a fresh, clean and wholesome smell.