My dryer vent runs 20 ft horizontally, and when the top of my dryer felt warm I new there was a problem. I purchased a brush with fiberglass sections that attaches to my drill. Ran that through a few times and then duct taped my leaf blower to the inside connection. I am not kidding it looked like it snowed in my back yard.

Its amazing how much faster clothes dry now.

Check it annually.