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Old 08-25-2008, 06:50 PM   #1
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Question about dryer venting


Hi guys, question for you about proper dryer ventilation, hope this is the right forum. I've got a 30 year old house that we just purchased. We discovered when we moved in that the dryer just vents to inside the drywall. It's an interior wall and there is no insulation in the wall. I went up in the attic and there's a vent at the top of the wall so apparently it just rises through the wall and vents into the attic. Is this a saftey concern? I dug out a bunch of lint from the wall from the previous owners and I'm concerned about the buildup.

What's the proper procedure for something like this in new houses? And what would we use to prevent a lint buildup in the wall even if we get it vented to the outside somehow? Thanks.

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Old 08-25-2008, 08:33 PM   #2
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Question about dryer venting


Venting a dryer into an interior wall is not accepted by the code and neither is it acceptable for it to lead to the attic. You must change this and vent the dryer directly through an exterior wall. Read your dryer installation manual for maximum distance that the dryer duct can run. Try to make it as short as possible below maximum distance. This may require moving the dryer closer to an exterior wall. This is a fire waiting to happen. So get this fixed immediantly. If you need to drill through concrete or brick, you can rent a core drill and diamond bit for a 4 inch hole or a heavy duty drill with a 4 inch hole saw to go through drywall, Plywood and metal siding. Make sure you check the outside where the hole will come through. You don't want the hole too close to electric meters, lines or gas meters and lines.
If you have drywall, also make sure there are no electric lines behind it. And do not drill through a rim joist as that is not approved either.
Run smooth solid metal duct for all or most of the run and if you have to, then finish the run with metal collapsable duct. Do not use vinyl or foil type duct ( also not approved) as these are not fire resistant like metal. Run the duct with the male end facing the exterior path. This will prevent lint from forming in the smooth solid metal duct.
The only part of this installation that will collect lint is the collapsable metal duct. But it will take 3 to 6 years before you may need to clean it. Home centers usually sell a cleaning kit for 4 inch ducts.

I believe I read that some say its ok to vent an electric dryer in the house. I have to disagree. Anything that provides a heat source can malfunction. Mold problems can also make an appearance from the moisture.

When this is all done, then plug up the holes in the interior wall and the opening in the attic.

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Old 08-25-2008, 10:04 PM   #3
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Question about dryer venting


Very, very, very solid advice from Rjordan392. I'd suggest the same actions, because this is absolutely a life safety issue.
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Old 08-26-2008, 12:21 AM   #4
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Thanks for the quick replies. Unfortunately there really is no other place for the dryer unless it goes in my dining room and the wife isn't going to go for that....

I can run an exhaust to the attic with no problems. From there should I continue up and exhaust through the roof? The other option would be to run a vent to the overhang of my roof. I'd prefer this since I wouldn't have to make a hole in my roof to worry about waterproofing. Both of these are within the allowable distance for my dryer. My concern still is where any lint that finds it's way into the duct would end up. I guess most of it will just pass straight through and come out the vent? Thanks for the help guys.
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Old 08-26-2008, 07:15 AM   #5
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Question about dryer venting


If using the garage, if you have one, to set up the washing machine and dryer is not an option, then I see no choice but to go as you plan. What distance does the install manual say for the dryer duct run? Does it also say how many elbows are allowed for that distance? You will need 3 elbows. One at the dryer discharge, another in the attic and then one at the soffit vent. The soffit vent is more preferable over the roof vent. You want to make sure all the moisture and lint leaves by the vent and not leak into the soffit area.
You did not say what the distance is for the horizontal run and the vertical run and my concerns are that if you are near the maximum distance, your dryer has to work harder to push the air and moisture. You may also need a backflow preventer in cold weather. Having none is like leaving a window slightly open when the dryer is not in use. So a few elbows and a backflow device does cut down on the flow of air and moisture. You must allow for this in your calculations. See if the install manual gives differant spec's for vertical runs.
Do not use the wall cavity as a duct. If 4 inch smooth duct will not fit between the drywall and the outside wall, then oval duct should fit. let us know of your progress.
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Old 08-26-2008, 07:32 AM   #6
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Question about dryer venting


Is it possible to go down through the floor and use the joist space to get to an exterior wall? Just a thought.
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Old 08-26-2008, 08:41 AM   #7
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It can't go down through the joist space. It's a 1 story house (no basement) built on a slab and that's part of the problem with relocating the washer/dryer. I would have to get water plumbed to the new location and that would be very difficult.

The maximum exhaust length with 3 90 degree turns for my dryer is 35 feet. I've got 10 feet to get into the attic and another 15 or so to get to the overhang that I would like to vent from. A run to the roof would only have the 1 90 degree turn and I could go 54 feet, which is way more than I need. I'd still prefer option #1 though.

I'm glad to hear they make an oval duct, I was wondering if I would be able to fit a 4" round duct in the wall. Should I stick with oval all the way or should I convert to round once I get in the attic?
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Old 08-26-2008, 09:23 AM   #8
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Question about dryer venting


I think the smallest size available is 3 inches (minor axis) by 8 inches (major axis). You will need to convert it to 4 inch round just before the vent. Someone with duct experience will need to step in and tell you if its economical to convert as soon as it reaches the attic.
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Old 08-26-2008, 09:43 AM   #9
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Just an added thought. You will probably get a lot of condensation inside the ductwork in the attic during the winter so make sure you put a little slope on it towards the soffit so that it doesn't drip back down to the dryer. Does anyone ever insulate dryer vent ducts in unconditioned attics to reduce condensation in the pipe? I would think the condensation would tend to cause the lint to build up faster.
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Old 08-26-2008, 10:23 AM   #10
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Quote:
Originally Posted by jogr View Post
Just an added thought. You will probably get a lot of condensation inside the ductwork in the attic during the winter so make sure you put a little slope on it towards the soffit so that it doesn't drip back down to the dryer. Does anyone ever insulate dryer vent ducts in unconditioned attics to reduce condensation in the pipe? I would think the condensation would tend to cause the lint to build up faster.
Sounds like a good plan, thanks.
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Old 08-26-2008, 11:37 AM   #11
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Question about dryer venting


Wrap insulation around the ducts in the attic. You can use plastic ties to secure it.

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