Dryer Lint

Factual Questions
1

So yesterday I took a closer look at the dryer lint system. What we have is a gas dryer connected from behind to a duct in the wall which runs up through the attic and out the roof. Occasionally when the dryer starts taking longer to work I’ve gone up into the attic and disconnected the duct there and cleaned out some lint, but I’ve never looked at the part behind the machine (we once got a guy to clean it but I wasn’t home).

Anyway, the flexible duct from the machine is connected to the duct behind the wall via an opening in the wall about 18 inches or so off the floor. But the duct in the wall extends about a foot or so below that point, and there’s an opening at the bottom of that duct, unconnected to anything but covered with a metal cover. I disconnected the flexible duct from the wall duct, and also removed the cover from the bottom opening. What I found is that the opening that the dryer was connected to and points above that were mostly unobstructed, but from that point and down was completely filled with lint. (Never seen such a large collection of lint in my life - if anyone needs any lint I have extra :)) So my questions are:

[ul]
[li]What determines whether lint goes up or down? (I’m guessing that it goes up when the exhaust goes up but that some settles down after the exhaust ceases to rise.)[/li][li]Is there any practical short-term effect of having the point below the dryer connection filled with lint? Or is the only issue there if it eventually rises to the point where it blocks the dryer exhaust?[/li][li]Does having a huge collection of lint in that bottom part make the attic/roof section clog up faster (possibly some of this stuff rises up?) or are these unrelated?[/li][/ul]
Basically, what I’m wondering is if someone can explain the structure of a lint-collection duct system like this one. Thanks.

2

I don’t know but dryer lint is extremely flammable so I’d clean that out immediately.

3

I think that’s a cleanout access point so you can use a long straight brush to clean the whole pipe.

4

How far up does the dryer lint need to go so that it’s exhausted out the roof? Because I don’t think the force of the dryer exhaust by itself is going to move the lint up very far.

5

I’m reading this and trying to wrap my head around the system you’re describing. Let me see if I have this right.

So, the dryer ducting leaves the laundry room and then, behind the wall there is some sort of T or Y, with one branch going down (terminating with the metal screen over the end) and the other branch going straight up through the roof. Or maybe the dryer vent pipe is one single run but has a bend of some sort and at the low end is the screen your found.

Do I have that about right? I’m still uncaffeinated so may be suffering ID-10-T problems. But that’s how I read that.

If I have that right, that begs more questions. First, where does the downward-pointing branch of the dryer vent end? In a wall? Basement? Crawl space? Dryer vents must be vented to the outside, as moisture being blown into the crawlspace (or basement or, God forbid, into the wall cavity) can—and will eventually—cause all sorts of problems. Moisture will cause mold and mildew to grow and potentially cause rot, the little bits of dryer lint that make it past the lint screen can accumulate and create a significant fire hazard (as you discovered).

I can’t for the life of me understand why a dryer vent would have two openings, especially if one is somewhere in the house. I’ve seen a few places where the dryer vent is routed through the roof, but they seem to cause a lot of problems simply because they’re hard to clean out and extends the length of the vent line—you want it as short as possible for maximum efficiency and lowest fire hazard. Additionally if you live somewhere where ice is a concern you could potentially have an ice dam buildup where the vent exits. If I were in your shoes I’d see what it would take to vent the dryer out the nearest wall, hopefully creating a much shorter run of vent pipe.

As I’m thinking about this I’m wondering… I’ve only used electric dryers, but if your dryer is gas then does the combustion gasses get mixed with the dryer exhaust and both sent out through the same duct? If so (and I have no idea if that’s the case, but it makes sense to do it that way) then you have added incentive to ensure that it’s vented properly outside.

Either way, I think you need to get rid of the second opening where you discovered the lint buildup. The dryer exhaust pipe should be smooth and straight as possible. In your setup I’m envisioning the pipe entering the wall from the laundry room, making a 90-degree turn and going straight up and out through the roof. There shouldn’t be additional elbows or bends and certainly no additional vents or screens. Keep It Simple and all that.

Since there seems to be a lot of lint bypassing your dryer’s lint screen you might want to invest in a supplemental lint trap that you can mount in the vent line before it enters the wall and hopefully reduce the amount of buildup in the line.

(Storytime: years ago my in-laws moved into a smaller house. The house had a carport attached with a small storage/tool shed attached to the carport but not the house. There’s about 6 or 8 feet of space between the house and the tool shed. Since this space is under cover my FIL uses it as a sort of storage spot for scrap lumber, old bicycles, and similar junk. However, the laundry room is immediately on the other side of the wall and the dryer vent exits the house about 4 feet up the wall, directly above his pile of junk. Since he never uses or even messes with that pile, all the little bits of dryer lint that have made it past the lint trap in the dryer itself accumulate on that pile of junk.

And has for 20+ years.

Today that pile looks like a giant, organic… thing. Whatever is under the three or four inches of lint is unidentifiable. It looks like a giant, mold-covered blob. I rue the day they pass away and we have to clean that disgusting mess. )

6

IANA general contractor or builder, so take this with whatever size grain of salt is necessary.

I’ve never seen or heard of a dryer vent clean-out or access point, and a quick Google search shows that if they even exist they certainly aren’t common. If that’s what it is I wonder if someone built it themselves thinking it would be beneficial.

Indeed, the vent pipe should be as smooth and as straight as possible. Avoid the corrugated metal pipe if at all possible (do NOT use the plastic stuff) and keep the bends and elbows to a minimum. Long runs of pipe reduce flow and can help create lint build-up. Additionally, any spot in the vent where lint can snag of accumulate will cause the lint to do exactly that. Some sort of a screen within the pipe would simply create more problems.

7

I would guess about 13 feet to the roof from the point where dryer connects to the wall duct.

I’ve not said anything about a screen. There is no screen anywhere that I can see.

The duct in the wall goes from about level to the floor (where it’s solidly capped off) up through the ceiling into the attic and on through the roof. There are two places in the laundry room where this duct opens into the room. One is about a couple of inches off the floor, and this is covered with a metal cap (not screen) - the cap has a handle on it and is evidently intended to be removed and replaced. The other opening is about a foot or so higher, and is connected to the dryer.

I don’t know if this was (solely) intended as a clean-out/access point, but in any event I am sure that it’s not something that someone built themselves. I had this house built from scratch and it was done completely to code (the inspectors in my town are notoriously tough - and the HVAC guy in particular - to the point where some contractors are reluctant to work here).

8

Ah, ok. Somehow I read that it ended in a screen, not a solid cover. ::goes and gets more coffee::

So you have two openings to the vent in the laundry room: one at floor level (the one with the cap) and one above that where the dryer itself attaches.

According to this page of building codes (see 504.3), “each vertical riser shall be provided with a means for cleanout.”

So I’m guessing sitchensis got it. It’s an access point for cleaning the duct.

Now that my brain is working, lemme take a stab at your actual questions.

1). Most of the lint should get blown out (note that the very next point on that list of codes notes that screens covering the exit point are prohibited because the lint that makes it into the pipe would build up on the screen). Whatever doesn’t should fall and collect against the cap you discovered.

  1. Dryer lint is extremely flammable. However, as long as there isn’t much accumulated against the cap you found the danger should be negligible—after all, the hot exhaust gasses are going up, not down.

  2. Having lint accumulate in the short section meant as an access for cleaning the pipe shouldn’t affect the airflow in the pipe as it’s basically just sitting there as the air rushes by above it. However, as you note, some may get pulled into the stream of air and pushed up. I imagine that would only happen if the lint accumulation got to the point where it was beginning to impede the flow of air.

9

I’m wondering why so much lint is even getting into the vent?

You should check the dryer to see why the lint is not being caught in the lint filter, maybe its installed incorrectly or is defective and doesn’t sit properly. Plus, make sure you clean it after every load if you’re not already.

I read some clickbait on how bad accumulated lint was - reducing dryer efficiency and being a fire hazard. Since we’d moved in to the house I’d never cleaned the vents and I doubt the old lady we bought it from had ever done it either. I bought a lint removal kit similar to this: https://www.homedepot.com/p/Everbilt-Dryer-Lint-Removal-Kit-BPCKHD/203626491

Bottom line - I barely got any lint out of it. A few pieces that maybe totalled to the size of my palm. I also brought it to my parents and did theirs. Same story - after never being cleaned for over 35 years, the total lint was maybe 2 palms worth.

10

It’s possible that you guys don’t do that much laundry. We have a big family and the machine is used quite a lot.

From looking around, I see the experts seem to recommend cleaning the ducts every year at least, and more often if there’s heavy use.

11

Maybe the difference us due to usage, but we have a family of four with young kids and are doing multiple loads a week. In our dryer, I’d guess 99% of the lint is caught in the lint trap on the machine. We clean that religiously, every single use.

I do clean mine annually now, but like I said, I get almost nothing.

12

In my area, building codes forbid the use of flexible dryer vent hose. The corrugated surface collects more lint than the smooth kind, and in case of a vent fire, the plastic will burn. Get the metal stuff.

The amount of lint that clings to the duct varies with the kind of fabrics you’re drying, and whether or not you use fabric softener.

Now, tools. Most of them are a round brush on the end of a long flexy shaft. Seems like most of them are 10 feet long. Here’s an assortment at Amazon. The Deflecto model can be chucked into a drill. If your duct is longer that 10’, as mine is, you can duct-tape the end of the brush to a electrician’s “fish tape” to extend it as far as you need. Most hardware and home improvement store will have at least one kind.

The vent cleaners: https://smile.amazon.com/s/ref=nb_sb_ss_i_7_10?url=search-alias%3Dgarden&field-keywords=dryer+vent+cleaner&sprefix=dryer+vent%2Caps%2C186&crid=3A505E4BKWPEJ

The fish tapes: https://smile.amazon.com/s/ref=nb_sb_ss_c_1_16?url=search-alias%3Dgarden&field-keywords=electrician+fish+tape&sprefix=electrician+fish%2Cgarden%2C179&crid=KJJ5TNTGLIG3&rh=n%3A1055398%2Ck%3Aelectrician+fish+tape

13

Weird.

I wonder if maybe the vent was originally going to go down and then underneath the floor to the outside?

2 unpleasant stories from our houses here.

Our last place, a townhouse, had the dryer in the basement. The vent pipe went up behind the dryer, then horizontally along the ceiling to a vent outside. So far so good. But then we developed a problem with birds nesting in the kitchen vent, so we put wire mesh over that - and did the dryer vent outlet for the same reason.

And forgot about it for years.

Well, that 12 feet or so of vent pipe wound up nearly completely clogged with dryer lint, to the point that it was full of soggy lint (no fire hazard here!) and was causing drips into the drywall ceiling. OOPS!!! :eek:

Our current place: whomever designed the ducting system had to have been on crack. The dryer is on the main level, almost directly above the furnace room. The vent goes down, through the furnace room ceiling, and is connected to flexible (as in, mylar with a wire spiral - totally flimsy), loops around a couple of other vents, then goes back (through the finished basement ceiling) to the back door. I seem to recall that the floor joists are perpendicular to the direction it needs to go, as in we’d have to cut holes in floor jousts to improve the situation.

Well, after a few years, that gradually became clogged and we bought some vent-cleaning tools. Something like this. My husband had to purchase an additional set of extensions, as the kit itself was not long enough. He managed to get several large bagsful of crud, but then we checked the loopy mess in the furnace room and realized he’d punctured that bit in at least one place. It was still so full of lint - soggy, nasty lint, that all we could do was put a basin underneath it and collect the drippings. It took several days before it stopped dripping, and he was able to finish clearing things out.

I can’t imagine how anyone put that kind of crappy ducting - there is stronger flexible ducting available.

In both cases, while dryer lint is normally a fire hazard, I think we were in no danger as the stuff was soaked. There were certainly other health issues if we’d breathed in much of that crap.

14

It just depends on the situation. At my parent’s house the vent is all solid pipe, not too long and about as straight as a run as you can get for their setup. However, once a year or so I’ll take a section down and it’ll be so packed with lint, the 10 foot section of pipe will feel like it’s filled with concrete. In fact, once or twice it actually fell off the adjacent pipe. I don’t know if it was the weight or the exhaust blowing against the restriction, but you’d think someone would have noticed the basement felt like a sauna.
OTOH, I’ll take mine apart from time to time and the most I’ve ever found in it is a little bit snagged on some of the sheet metal screws. It wasn’t even worth the trouble of taking it apart, though I do want to clean out ducting inside the dryer itself at some point.

Then there’s the case that I either read here or saw on imgur where the exit (to the outside) had insulation stuffed in it and the duct was packed with years worth of lint. That thing probably wasn’t drying properly almost since the very beginning.

From time to time I’ll poke around in the exhaust, from the outside, with a stick or a long piece of wire, while the dryer is running and a handful or so of lint will come out. The thing you linked to looks like the same idea.

15

I have to clean mine out at least one every 3 months. Typical house in Chicago has a small section of solid leading to outside and the rest is that corrugated flexible type. Stick a messed up clothes hanger in it after you take the grill off on the outside and clean it out, then replace the entire section of corrugated on the inside. Takes about 20 minutes, the biggest pain in the ass is reaching the worm clamp at the bottom since a slop sink is between the washer and dryer. I wash and dry clothes 3 times a week, and those things get really insanely filled with lint. Having a permanent smooth duct doesn’t make sense to me, moisture and condesation will cause it to stick and build up, the corrugated it seems to stick loosely.

Just my 2 cents.

16

May I suggest a simple solution that may help eliminate most of the lint problem? If you have the room, construct a box of anything Preferably out of sheet metal about a foot square and several feet long, (the longer the better). install a coupling in one end to attach the pipe from the drier leaving about 2 to 3 inches protruding through inside.
Attach another adapter to the other end that goes to the outside exhaust. Use a Ladies silk hose (or part of a panty hose) to slip over the 2 or 3 inch portion on the input side from the dries. This will catch almost all the lint. Just don’t forget to clean it out occasionally. Be sure the top access door is air tight. This works fine. Some people I know from long time ago didn’t have an outside vent and only used the silk
hose!

17

An additional in-line lint filter (which is what you’re describing) is fine as long as you’re committed to cleaning it out often. And OP’s situation is a gas dryer, which you can’t vent into the house unless you love dying of carbon monoxide poisoning. (Never mind that venting into the house, even when safe – an electric dryer, for instance) would make the room vented into very hot and very humid during the drying cycle. In some climates (near-Arctic), this may be temporarily acceptable.

18

It’s a good idea. We had a lint fire many years ago. Luckily, it only amounted to a brief ball of flame, then went out, but it scared the crap out of my ex.

19

So, suppose that you run a wet load of clothing through the dryer when it has a half-blocked, linted-up lint trap. (Half of the trap is free and still lets air pass through.)

  1. If the dryer temp is 135 F, does that mean it can’t build up to higher than 135 F? (unless that means that incoming air is actually something more like, 150 F?)

  2. How much of a fire hazard is a one-time mistake of that? (running the load without having cleared the lint trap)

20

Finally, how hot usually is the temperature that makes the dryer’s thermal fuse go off?