How often should the clothes dryer vents be cleaned?
Once a year is the recommended time from most manufacturers. Remove the vent from the back of the dryer and use a shop vac to suck out the lint. Also your lint filter should be done twice a year. A quick test to see whether this film exists, is to take your filter to a sink and run water into it, while observing whether the flow can easily pass through the mesh, or just pools in the filter. Use a very soft nylon brush and warm soapy water to clean your filter, and repeat the above test – the flow should no longer be restricted.