Online it says 35 ft max
Book that I purchased a week ago says 25ft
I studied the book since i didn’t have access to a computer and took the online quiz after I came home and got that answer wrong. Went back to read it online and see that its 35ft instead of 25ft max.
The maximum duct length should be 35 feet but it can also be determined by the manufacturer
https://codes.iccsafe.org/content/IRC2018/chapter-15-exhaust-systems
Thank you @jyoung32
May still be 25 feet in some jurisdictions. Not everyone is operating off the newest code.
Either answer should not be wrong. Test questions should be changed to anything over 35’.
Better question: do you know why it was increased from 25 to 35?
Big money, big homes. Money always talks… 
Nice try, but no 
Then why the 10’ change? Ahhhhh!! The architects/ builders that can’t make their design work…Lol!!
I’ll give you a hint, the same reason why the standpipe for clothes washers increased from 1.5 to 2"
The 1.5” standpipe could not handle the volume from the clothes washer.
So 35’ feet of a dryer vent can’t handle the extra air push from a dryer without larger sizing? Just asking based on @srechkin analogy?
Code changed in 2012, I would say it has to do with newer more efficient dryers being the market. @srechkin It could also have something to do with more efficient washers on the market.
Tony with the sensible answer and the fact the “code” has changed and not been updated…like the test questions. 35’ is what it should be based on (along with manufactures installation) and all the other requirements.
If I had to guess I would say modern clothes dryers are similar to modern clothes washing machines. The pumps are very efficient and more powerful than they were 20 years ago. It is possible the exhaust on a modern clothes dryer is capable of easily traveling 35 feet.
They’re probably aren’t many washers and dryer‘s from 20 years ago still in service today.
Yeap! 
The fan is now powerful enough to push through 35feet of vent, that simple.
I can tell you this Simon my new clothes dryer can dry a full load of clothes in less than 20 minutes.
Yeap, people want everything NOW, they no longer can wait – or the world is going to end in front of their laundry load
Not joking… I prefer to “air” dry mine. I do so during summer, weather permitting. Dryers kill clothes.
Probably, but mine are close going on 18 years with our Whirlpool washer and dryer. We probably won’t get new until they are dead dead. We’ve moved them to 4 places because we know they how well they work.
Thus the requirement should note " depending on…25’ to 35’ should be max.
just going back to the OP’s question and why one or the other is wrong on a test.
