TOPIC: Dryer pipe

I was in a house today that the dyer pipe was about 20 + feet long. This seem to be long but just wanted to know if there is a lenght requirment? The reason for the lenght is that it was a semi-detached house and it was going to the closes wall out.
Don

Our laundry room is in the front middle of the house and the dryer vent goes down from the laundry and out of the back of the house.  The length of the pipe is 33'.  I don't know if there is a length requirement, but the fact that the vent you refer to went to the nearest exterior wall is the most important thing.