Just purchased a new dryer and trying to upgrade my venting system. I have rigid 4" pipe on about a 20 ft run from laundry room to outside. My problem is getting from the back of my dryer to the straight run. Here are some pictures. Feel free to jump in. I HATE flex ducting. Opinions? I can't cut any farther to the right as the current cut is right up against the floor joist. I can cut more to the left. You can see my 4" rigid pipe is pretty tight as it is. The vent in the dryer will not line up with the current hole as it is more to the right and I can't cut the floor joist.
I think I would build a raised platform from 2"x 10"/3/4" plywood to gain more clearance for venting. Make a easy opened access panel at bottom to hook up the vent when dryer is setting there. Does the dryer have a optional bottom vent outlet? Mine did. If so you could use that outlet. Raising the washer/dryer would also help the bending over stuff. Can you return dryer and get a bottom vent if yours doesn't have one?
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Just looking at it some more, I think one adjustable elbow to get it pointing up and then flex the rest of the way. Get a hinged cover plate to hide the gap where the duct comes through the floor. Covering up the rest of the hole will finish it off.
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- Look at the dryer owners manual to determine longest allowable vent length. It varies by brand and each elbow (90 or 45) reduces the allowable length considerably. At 20 ft. in your OP, you are getting close to maximum with any elbows. There are long vent dryer models and booster fans. Whether you use flexible metal or 3 els. described above by SWS, you need to adhere to maximum length guidelines. - Duct hidden within walls/floors must be rigid. UL transition duct from dryer to rigid can be flexible. - Floor trusses(not joists)..... any chance you can re route the rigid pipe in the floor trusses to come up further to the right. This would require a new hole. - I would explore the products of companies like Builders Best and maybe Dundas Jafine to look for problem solver products. http://www.buildersbest.com/product-industry/dryer-vent-kit/
Here's one example of UL listed semi rigid flexible transition duct:
EDIT: just noticed that the final piece under the floor is an adjustable elbow. You should be able to make it turn up a bit to allow smoother transition to the flex pipe.
My last dryer allowed me to vent downward by installing an elbow This way it vents out the bottom and not the back. Maybe then it would move farther left. Just a thought. Thats how I did mine and then you can push dryer right against the wall.