My dyer is in the basement and behind the dryer is a periscope duct inside the wall that runs from the floor up about 5 feet or so and goes outside to the crawlspace. That was probably originally vented to outside but a room addition was built above where the vent discharged so it is now crawlspace. Anyways, from the end of that vent, semi-rigid duct is run inside the crawlspace which discharges into a flapper style vent that vents outside. I want to replace the flapper vent because it does not shut all the way so I probably want to get a better style and I also noticed the semi rigid duct is just laying on the ground in there anyways until it gets to the vent. It has been that way since I had the house (over 10 years) but am wondering if that is ok or if I would be better off running rigid duct through the crawlspace to connect the periscope to the outside vent. Running rigid would require at least 3-4 elbows to account for the elevation change and to get it around beams and ducts.

 

You should use rigid and you should pitch it down towards outside so the lint moves with the air.
Get the variable angle elbows and try to use them less than 90°. Two 45°s are much better than a single 90°.

 

Not sure what "semi-rigid" means, there is solid/hard duct and then there is the krappy flex duct.

Any thing flexible will collect lint, that can lead to fires so best to eliminate!

 

I could try that. The top of the periscope duct is higher than where it discharges outside so I could try to run it downhill and at an angle so there is less of a run and less sharp turns. I have never installed this before, so how do you connect the pieces? It looks like one end is tapered to fit inside of another piece, but how are they secured? Also, can you recommend a good vent for outside? The flapper type i have now has a guard around it that I clean lint out of every month or so, but it doesn't shut all the way anymore. Is that still a good kind, or are louvered better? Or something else? Thank you.

 

WIth screws, they probably have a name, but they are hex head with a point that helps get them centered and started in the metal, usually 3 per joint with foil tape to seal!

 

I do not use screws in dryer duct because the ends can catch and accumulate lint. Foil duct tape will hold and last a long time.

 

I also use duct tape, preferably the foil type. If the duct is secured well with hangers it doesn't take much to hold it together.

 

For those who do not want to use rigid duct work, there is a semi-rigid that I will recommend. Not that tin foil crap, but this stuff...https://www.homedepot.com/p/Smart-Choice-8-ft-Semi-Rigid-Dryer-Vent-5305512431/204188345?cm_mmc=Shopping%7CG%7CBase%7CD29A%7CMulti%7CNA%7CPLA%7CMajor_Appliances%7c71700000032407466%7c58700003840694625%7c92700030982803212&gclid=CjwKCAjwstfkBRBoEiwADTmnEP3oGtSx8cGHqBywtKP9oTvYmNX7qRF4ZcaUMr3-2_LgCzSrSA2q6hoCnGcQAvD_BwE&gclsrc=aw.ds

Not the best but better than the tin-foil.

 

I've taken apart ducts that had never been cleaned and the amount of lint stuck to a screws is miniscule, that is of course assuming you use the 1/4" screws not something 1" long.

 

That's cool, Marq. I've seen screws in perfectly clean ducts too, and I've seen ducts without screws that were packed right full of lint, so wasn't advocating or debating. Didn't say "shouldn't use screws", just provided another option, along with the reason, right, wrong, or of zero consequence that I do it.

 

Dryer vent duct work should be check and cleaned at least once a year. I should also practice what I preach.

 

Dryer ducts are a double edged sword. They need to be sealed but they need to be removable to be cleaned. Using something as smooth as rigid vent pipe with no screws is the best way to go.... especially in horizontal runs,

 

That semi rigid that Norm posted is what is in there now. It probably has a bunch of lint in it. I also read about not using screws, but that seems crazy that a little 1/4 inch screw will collect lint, but it also makes sense since the rest would be smooth. What about clamps to hold the pieces together? Or tape with a clamp over it? What type of vent hood do you guys like?

 

The best is all rigid, force fit with no screws or fasteners.What PJ says. I use all rigid with no screws. However, occasionally the elbow from the dyer unit tend s to work loose.

 

The rigid pipe force fits together, adding tape to the joints makes it a little more secure.

 

I tackled this project today and while it took a little longer than I thought, I got it done. I guess there isn't a periscope in the wall afterall, it looks like they just ran 4 inch duct in the wall with an elbow at the top and bottom. The old flex duct in the crawlspace had quite a bit of buildup in some places where it was damaged. I had to put one 90 to get it down under the joists and other ducts but the other bend is about a 45 or less. Anyways, when the dryer was installed, they put some 90 degree piece that goes into that flexible stuff and it makes a big loop around before it goes to the wall. It looks like they did that because of the offset and that seems pretty inefficient to have a 4 foot looped piece of flex line to go from the dryer to the wall when it is only offset about 6-8 inches. I think I would be better off just getting two 90 degree solid elbows and adjusting them so it will fit instead of having this big loop of duct back there. When I took that out, there was a big ball of lint in it. Thanks again for the help.

 

It they used semi ridge is OK and the loop lets you pull dryer out for servicing.