Restricting the duct could affect the dryer's performance. If going up inside of the wall is your only option, then I suggest using oval duct. It will have a larger capacity than the 4" round and is made to fit into walls. You may have to get some transitions from oval to 4" round fabricated to put on each end. Any sheet metal shop can do this.
It is better to run the ducting outside the wall. That's the only way I've ever seen it done and there are several good reasons I can think of. 1. The insulation of what is presumable an exterior wall will be compromised far less. 2. It will be easier to access or service ithe ducting n the future should the need arise. 3. That vent will get hot and could be a fire hazard if placed inside a wall.
I know it sounds neat to hide the vent inside the wall but I do not see it as a good idea
You must have a duct with the same cross-section area as the 4in duct. Since a 4in duct has a cross -section of about 13 sqin, you must have a rectangular duct of at least that cross section.
I have done what you are trying to do; installed a dryer on the second floor and moved the vent up a wall, into the attic and to the top of the roof. Total linear footage is about 12 feet, vertically, with only one bend, the 90 degree between the dryer and the wall. My 4in duct goes into a rectangular 3inx10in heating duct, and then connects at the roof with a 4in discharge vent. I thought that I might have a problem with the velocity of the discharge (since the area in the rectangular duct is much larger than the area of the 4in duct), and I have checked periodically to see whether lint accumulated at the bottom of the rectangular duct, and none is present. That's been seven years since I moved our laundry room to the second floor. I have had no problem whatever. FWIW, it's a Maytag Neptune gas dryer.
Yes, I have a pan connected to a drain under the washer. Thanks.
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