Dryer vent question

New construction.

I want to install a dryer vent to a centrally located laundry in a standard 1 story ranch. I have a choice of going straight vertical (8ft room rise plus approx. 8-10 ft in attic. It's an 8/12 pitch roof so there is alot of vertical distance in the attic. The vent would terminate on the back side of the roof.
The other option is approx. 8 ft vertical rise and then 90 to an approx 10 ft horizontal run to exit into an exterior gable end wall above the driveway.

What is the best option here? Depending on the answers, I may have a lot more questions. Thanks in advance for any help.

Straight through the roof will give you less restriction than using the 90. The run lengths are about the same. It would be more what you want it to look like as far as where it terminates. Use solid pipe for the run.

Your dryer installation specs should give you the maximum horizontal and vertical runs. and max number of elbows. Either of your methods is probably within specs. BUT, dryer efficiency is directly impacted by the exhaust run. You would be well advised to install an exhaust booster. They are not expensive, and have a sensor such that they turn on automatically whenever the dryer runs.

dryer

The vertical run will give you a lot less problem with condensation, and also lint buildup.

Thanks guys for the replies. Jimbo, thanks for the heads up on the booster fan, I didn't know they existed.

Cass, when you talk about smooth pipe are you thinking metal or PVC? It seems that PVC at least outside the roof would be a more long lasting choice.

I'm leaning toward the straight vertical installation with 3" or 4" PVC pipe.

I've read that the IMC (Intl. Mech Code) requires that dryer vents be a max of 25' and this distance should be reduced by 5' for every 90. I was thinking of exiting the roof with PVC and then terminating with 2 4" 90's, creating an upside down "J" such that the dryer exhaust would exit straight down toward the roof and rain can't enter the pipe. But the distances might not work (and the concept may suck too). I dunno. That's the way my current house is, but the distances are much shorter.

Any hints on other ways to terminate this thru the roof, without the 2-90's. Is there a rain cap type fitting made?

One final question- can you easily transition between standard metal flex dryer vent needed inside the laundry and PVC which I would like to use for the vertical run?

I'm not sure about PVC. When I said smooth pipe I ment galv. steel pipe.

If you terminate towards / at the roof, over time you may get some visible lint build up.

Not a pro by any stretch but, based on my experience, you WILL get lint build up - particuarly if you terminate the outlet with any sort of weather cap.

If you execute your "J" idea you'll get build up on the roof (not to mention possible back drafting) unless the J is well above the roof level. If you use a weather cap then the lint will build up in it over time and you'll be on the roof cleaning it out from time to time.

I'm thinking the verticle run to above the driveway. That way you can at least keep an eye on it to ensure it's clear of lint, and get to it easily if it isn't.

Insulate the verticle, and pitch the horizontal towards the outlet.

JMHO....

Dan

The pipe needs to be smooth wall AND metal. The only exception to smmoth wall is a short section of corrugated to make the final hookup at the dryer.

If you don't have a damper on the outlet, expect a significant draft into the house whenever the thing is not running, and birds nests , the occasional squirrel and who knows what coming down that pipe.

Thanks again Jimbo and also thanks to ss and Jim. I'm still mulling this over and appreciate the ideas. The joist layout in the basement precludes running thru the floor and and then horizontal between the joists . There's a garage at the end of that run. I don't want to go into the basement and then turn 90 under the joists because I would then have to rise up again with fittings to get thru the rim joist, thus creating a puddle in the pipe.

Going vertical and then turning 90 thru the sidewall to exit above the driveway may be pushing the limits. This would mean a 90 thru the laundry wall then 8 ft rise thru ceiling, then 90, then 12ft run to sidewall. If I go straight vertical then the distances are the same with one less 90. Just have to figger how to terminate at the roof.

Like I said, I'm still mulling it over. I appreciate the comments, they keep me thinking. Jimbo, still looking into that booster idea.