I came up with this:
The International Mechanical Code article 504.6 stipulates the requirements for Domestic clothes dryer ducts. In brief, the maximum length of duct permitted is 25 ft. This maximum length should be reduced by 2.5 ft for each 45-degree bend and 5 ft. for each 90-degree bend. The duct should be a minimum nominal size of 4 inches in diameter and shall have a smooth interior finish.
Appears the 2009 edition changed it;
**[FONT=TimesNewRomanPS-BoldMT][size=3][FONT=TimesNewRomanPS-BoldMT][size=3]504.6.4.1 Specified length. [/size][/FONT][/size][/FONT][FONT=TimesNewRomanPSMT][size=3][FONT=TimesNewRomanPSMT][size=3]The maximum length of the
exhaust duct shall be 35 feet (10 668 mm) from the connection
to the transition duct from the dryer to the outlet
terminal. Where fittings are used, the maximum length
of the exhaust duct shall be reduced in accordance with
Table 504.6.4.1
[/size][/FONT][/size][/FONT][FONT=Arial-BoldMT][size=1][FONT=Arial-BoldMT][size=1]
**[/size][/FONT][/size][/FONT]
ahh Marcel, this is not from the IRC my friend. 
The correct answer is 25 ft.