I like to think that I use my own residence as a test study for things that we do for our clients. Recently, as I was driving home I noticed two fire trucks coming down my street. I didn’t think of any relevent issue until I arrived at home and told my wife about it. She said that she had received a phone call from a neighbor down the street that she smelled smoke from her dryer and called the fire department. She explained that she had a build up of lint in her exhaust vent and that was the cause. The next day my wife called the gentleman that cleaned out our neighbors vent to come and examine ours. That night I opened the front panel of the dryer and was amazed at the amount of lint laying around the mechanical parts of the dryer. This was a safety hazard. When the service company came we were amazed as to the amount of lint that was removed. The amount of lint that had accumulated in the vertical stack was unbelievable. We were told the vent should be cleaned out every one to two years. After this experience I would instruct you to have your vent examined if it is veritcal and extends to your roof. Even if it goes straight out the wall behind your dryer, you should still have it inspected. You should service your vent every year or two, it sure beats having a fire.