http://www.bengromicko.com/images/dryer-transition-duct-length-ben-gromicko.jpg
Clothes dryer transition ducts should be metal, should not be concealed within construction, and they should be limited to a single length not more than _____ feet.
What’s your answer? (try to refrain from looking it up 
)
Seems I remember 8ft?
I was thinking 6…
8 feet
6 ft.
6 Feet
I am revising my answer…
8 feet for IRC
6 feet for UMC
It depends on where you live and what code they are enforcing.
Although sold in 8’ lengths, needs to be installed per the Manufacturers installation requirements and listed for that installation.
Even better, install one of these and elliminated the lint collector venting.
Here is an actual installation.
Marcel,
I’m not quite sure I understand what your showing here.
That looks like a box, inside the wall, inside which the end of a smooth-metal dryer duct is extended, ready to connect to a flexible duct to the dryer. Yes?
Many vents are further than 8’. Depends on the age of the dwelling and the location of the utility room, which in many instances, was rougly dead center.
You can have a 28’ deep raised ranch, with the dryer installed in a utility room, on the ground floor in the center of the dwelling. Distance to exterior wall may be 10 feet as a horizontal run, with a vertical run of 8’ and two 90 degree elbows.
I see it every day and simply state that the configuration is potentially problematic and may not meet current code requirements. Additionally I state that there are more dryer fires annually than chimney fires, and thay should have the dryer vent cleaned twice a year.
If I spend more than two minutes looking and evaluating the existing condition, I am spending too much time on it, IMO.
Transition ducts…Scott’s got it.
That’s what it is Ben, a Dryer box that only needs 2’ of flex duct and the dryer can be pushed close to the wall without kinking or crushing the duct as we see too often. Smooth duct from that point on. 
the flexible style dryer connection adds 10 feet, in the distance
the straight metal is 6 ft, i think
Transition ducting is not calculated into the length of the dryer vent to determine the maximum length. I don’t know where you were going with the straight metal comment though.
6 feet here in my neck of the woods… and none 'o that silly vinyl crap.
If it vents or extends vertically a trap should be installed. The other thing builders forget while on the subject is back draft prevention devices.