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25 feet is the maximum length for a dryer vent; any length longer needs to have an inline supplemental fan midway to push the air out. I would recommend that the entire pipe be rigid 4" metal duct. This length does make the dryer work harder, in that drying times will take longer; the shorter the duct run, the faster the clothes will dry- thus less energy and less money to run. Rigid metal duct is smooth and allows the exhaust air to flow better and more efficiently. Ribbed flexible duct, makes it much harder for the air to move and has a higher potential of lint build-up, which is a fire hazard. It is against code to use any vinyl type flex hose.
I would not recommend using any system that blows the air back into the house. I know that these kits were being sold, but they are not good; they dump too much moisture back into the house, raising the humidity levels and increasing the growth of mildew/ mold, leading to decay of materials.
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Best of Luck, Brian
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