Why is my dryer taking longer to dry clothes?
This usually happens because the dryer vent is getting clogged with lint (the lint-catcher isn't 100% effective, so some does escape).  You should clean it out regularly because a clogged vent can cause fires.  If the vent is short enough, you may be able to use a vacuum cleaner to clear it; otherwise use a dryer vent brush (can also be called a dryer duct brush) to reach the places the vacuum can't: