My uncle and aunt were 3-4 pack/day smokers (each) for 50+ years, till he quit. She smoked until her death. We went to the house the day prior to her funeral and were completely stunned and amazed. The carpet/drapes/walls/furniture were all still smoke-stained and yellowed, but the air in that house bore no trace of the fact that there had ever been a cigarette in it at all, much less two heavy smokers since the day they bought the house. My cousin had rented a ozone machine and ran it continuously for 2-3 days, and it was amazing!!