Dryer ducting is what I use my friend. You answered your question before i could post. Another good thing to get is a "Y" fitting for the intake fan. Then you can run two small pieces of ducting to opposite sides of the closet. The "Y" fittings cost about $5 or $6

In this pic you can see that I have partitioned the closet into two areas. All my equipment is on one side and the intake and exhaust are at the top and bottom. (well I guess you cant see the exhaust fan but just imagine another fan just like that one bolted to the ceiling. lol) I have a "Y" to distribute the intake air all over the grow room. It's also helpful because you will need to direct the air as the plants grow. Sometimes foliage gets so thick that it blocks the air flow.

Laterz