With air moving through the garage, you will minimize the corrosive effects of clay/ glaze fumes on exposed metal in the garage and on the outside of the kiln. There will still be fumes, though, and to see the beginnings of corrosion on the outside of an unvented kiln after the first firing is not unusual. With the kiln vent properly installed, ALL the fumes are exhausted, which makes for a lot less corrosion on and around the kiln. Additionally, without the kiln vent, fumes are left to leak slowly out of the kiln. The extra time they spend inside causes the heating elements and the thermocouple to deteriorate more quickly than they would with the vent. Some people get 40% longer element life when they add a kiln vent. While it is not a necessary accessory, we highly recommend it as it pays for itself in overall longer kiln life.