Lint can build up in your gas or electric clothes dryer's exhaust vent until it blocks airflow from the dryer, eventually causing the appliance to overheat to the point where the trapped lint catches fire. To prevent this problem, you should clean out the dryer vent once a year -- or whenever you notice warning signs of a vent clog. You can hire a vent cleaning company or buy a do-it-yourself vent cleaning kit from a home center.
Increased drying time can indicate a clogged dryer vent. A dryer must push out hot, moist air for clothes to dry, but a blocked vent can double or triple the drying time. Another warning sign is if the dryer and the clothing get abnormally hot, almost too hot to touch. That means heat is being trapped in the dryer. A burning smell while your dryer is operating means trapped lint may be heating to the point where it could ignite. Check the outside vent hood flap -- if it's not opening because of lint buildup, the airflow that carries lint away is blocked and you should clean the vent out immediately.