Clothes dryer designs

[Stephen Tashiro]

Are their any clothes dryers that pull air directly from outside the dryer to go over the heating element and into the drum?

The dryers I've taken apart pull air from inside the dryer cabinet to go over the heater and into the drum. I can see that this design might be more efficient since the air inside the cabinet is pre-heated by what's going on inside. But the inside of the cabinet gets a lot of lint in it and the air inside is probably more humid that the outside air.

[Bill Howatt]

Most of our dryer use is in the winter and -20F or colder outside air to heat up isn't exactly what we are looking for. I agree outside air is dryer in the winter but in an AC house it certainly isn't in the summer. Of course, things in NM aren't the same.

[Stephen Tashiro]

Most of our dryer use is in the winter and -20F or colder outside air to heat up isn't exactly what we are looking for..

I'm thinking of "outside" air as being the air in the room where the dryer sits - as opposed to the air inside the dryer chassis. (Of course, if it sits in an unheated area, I suppose -20 F is possible.)

[Mark Wedel]

The air in the dryer chassis is coming from somewhere - most likely from the room itself. I could imagine there is a slight increase in efficiency by using the chassis air, as that is probably warmer than the room air (which will replace it)
I've not looked, but wonder what electric heat pump dryers do - in theory, those could be more closed loop - one side of the heat pump warms the air, passes it over the clothes, this hot and humid air then passes over the cold side of the heatpump, which dehumidifies the air and recovers some of the heat before going back to the hot side. Though in that case, you would need a drain for water so condensed, which might be more an issue for some dryer install locations.

[Stephen Tashiro]

The air in the dryer chassis is coming from somewhere - most likely from the room itself..

Given how much lint builds up inside dryers, I'd say a lot of the air in the chassis is leaking out from the drum. I guess that counts as recycling some air.

[Bill George]

The air for the dryer comes from room air and then goes thru a Lint filter and should be exhausted to the outside the building air. Otherwise the moisture would never be removed from the wet clothes.

[Roger Feeley]

I think we are missing the point here. Stephen is right. I have never seen a clothes dryer with a defined air inlet. The air comes from the room and through the cabinet to a blower. I don’t doubt that this leads to lint buildup inside the cabinet.

so the question is whether there’s a dryer out there that has an air inlet duct.

my answer might not be exactly what you want Stephen. I have a ductless dryer. They are very popular in the EU and are catching on here to in apartment and condos. In my dryer, air flow is a closed circuit. Air flows through the drum and picks up moisture. Then it goes through a dehumidifier condenser. At some point, it blows excess heat into the room but it’s dry air. The water is collected and is pumped out to a drain. I have to remove the condenser plates a couple of times a year and rinse off the lint. No big thing.

so, as far as I know, my dryer would meet Stephens test.

[Bill Howatt]

I'm not clear on the lint build-up mechanism but I have seen it in old dryers so I'm certainly not denying it.
The lint comes from the clothes being dried - not the room. So why is it worse that the air comes from the room rather than an outside duct. The lint is in the airstream after it goes through the dryer, not before. Is the issue, that the "hot waste air" is not being ducted to the filter properly?

[Stephen Tashiro]

The air for the dryer comes from room air and then goes thru a Lint filter and should be exhausted to the outside the building air. .

I agree that it should do that theoretically. However, since lint comes out of the drum and gets into the chassis, it's clear that some air is also coming out of the drum - at least in the dryers I have opened up. A dryer designed so the blower sucks in room air through an inlet in the chassis and blows it directly into the drum would use room air exclusively. But that is not how the dryers I have seen are designed.

[Stephen Tashiro]

Is the issue, that the "hot waste air" is not being ducted to the filter properly?

If you are talking about the issue of lint build up inside dryers, yes, it is because not all the hot waste air is ducted through the filter. There are many felt seals in dryers, including a felt seal around either rim of the drum. I think these are a leaky type of seal.

Before I took apart some dryers, my guess about their operation was that there would be a direct path from the outside air over the heating element and into the drum. This is not the case. In the typical dryer, a blower sucks air out of the drum and blows it out the back of the dryer. The inlet to the heating element is not directly connected to room air. It takes in air from inside the chassis near the front fo the dryer. There is a vent to admit room air at the back of the dryer and the chassis itself is not air tight. Lint from the chassis can get sucked over the heating element since the inlet to the heating element has no filter. It's common to find burned bits of lint around the heating element in a used dryer.

In spite of that disadvantage, I assume there are reasons why this design is used.

[Tom M King]

Not exactly to the point of this thread, but something else to think about with dryers. When I was building new houses, I had to design them anyway since a lake house needs two fronts-one on the road side and one on the water side. One thing I always did was put the dryer backing up against an outside wall so it direct vented through the wall, so that no flex hose was used or needed. I expect we all know how lossy flex hose is, and that they always accumulate fine lint from dryers. The wall vent was removable and in a panel that it could be located in a different spot in the future if needed. You could install the wall vent after the dryer was in place.

[Lee Schierer]

My pet peeve with dryers is why the interior cabinet duct work is so convoluted and small that it is impossible to clean your the lint that gets past the lint filter.

[Stephen Tashiro]

One thing I always did was put the dryer backing up against an outside wall so it direct vented through the wall, so that no flex hose was used or needed.

I'm curious how you arranged that. Did you have a standard type dryer vent with a door flap to keep bugs out? How do I arrange the connection so the dryer can be pulled away from the wall when the need arises. One thing a flexible hose does is give enough slack to pull the dryer out enough to work behind it.

[Tom M King]

It goes directly into a standard wall vent with flap. Once the vent is in the right place, the dryer can be taken out and put right back. Just a friction fit but the dryer stays in place fine. Feel in the cap from the outside to make sure it’s being slid in correctly. We’re probably on our fourth dryer here, and I’ve never even needed to move the wall cap.

[Tom M King]

I have one I can take a picture of tomorrow in the rental house. It goes out the side to a direct vent through the wall. Since it’s out the side I can see it with the camera.

[Bill George]

It goes directly into a standard wall vent with flap. Once the vent is in the right place, the dryer can be taken out and put right back. Just a friction fit but the dryer stays in place fine. Feel in the cap from the outside to make sure it’s being slid in correctly. We’re probably on our fourth dryer here, and I’ve never even needed to move the wall cap.

So all the noise and vibration gets transmitted directly to the wall. Here most of the washers and dryers are in the basement, dryer vents are usually low so your direct venting would not work.
I use metal hard pipe not flex pipe to the outside vent with the flapper of course.

[Bill Dufour]

I use a snorkel vent. Metal no plastic.
Bill D

[Tom M King]

Never heard any extra noise, and no one who bought one of my houses ever complained about it either. We have two going in our house at the same time sometimes, and we never hear them. No dryers in basements here in my houses, although all the spec houses on the lake have daylight basements. I think maybe even more noise might be transmitted through plastic dryer hoses. It might be louder on the outside though. I'll check the db on ours to see, but I'm sure there is no extra noise.

I've been doing them like this since the mid 1970's.

[Mel Fulks]

I remember that years ago , 1960s ? The clothes dryers were used by college students to see how many turns ,or minutes , they could stand. They boldly rolled in their small piece of space ! Heat was available, but there was no air conditioning !

[Tom M King]

I either forgot to remember that we had people coming to the rental house this weekend, or that today was Friday. In any case, I'll try to remember to take pictures of that dryer vent and dB readings next week. Pam, who can hear a lot better than I can, says that there is no dryer noise, and they're all much quieter than the washing machines.

[Tom M King]

dB of our dryer in the dogroom running, which is such a direct vented one as are all the ones I've installed, is 62 to 65 dB three feet in front of it. I just checked it a few minutes ago. Couldn't figure out how to take a screen shot with the phone ap. dB of 24" fan running 24 feet away was 76. dB for dryer may have been less if I turned that fan off.

[Tom M King]

Here's the picture of the side exit dryer in the rental house. The old one that was in there had metal flex 4" hose behind it and running around to the side to go out this exit. That flex hose was pretty smashed up from the dryer being pushed against it, and probably stuff getting dropped on it.

Pam said the old one never "worked very good". We gave the old washer and dryer to someone who needed them and wanted them. They said the dryer works fine. I expect it was the restricted vent.

I used the side exit kit for this dryer and had to use a little bit of the flex dryer hose because the exit through the wall was a little higher than where it came out of the dryer. This allowed us to push the dryer all the way back against the wall.

It works fine. dB right in front of the dryer is 69 to 71 dB, and without the dryer on the AC vent in there is 44 dB. I didn't turn the system off to check the noise. When I put the phone down beside the dryer where the vent is, it read 82 dB.

I don't see that there is any benefit to using any length of flex hose. I would rather not have had to use even this little bit, but had to work with what I had. I didn't build that house. This is the longest dryer hose I've ever used. The block of wood between the dryer and baseboard is to keep the dryer from getting shoved and damaging the pretty fragile flex hose.

The dryer had a knockout cover where the side exit comes through the side. https://www.amazon.com/383EEL9001L-Perfectly-Compatible-Dryers%EF%BC%8CReplacement-PS7784989/dp/B0BDRJRG8C/ref=sr_1_3?hvadid=409938671727&hvdev=c&hvlocphy=9009786&hvnetw=g&hvqmt=e&hvrand=6890821039223645608&hvtargid=kwd-5018985405&hydadcr=24632_11410076&keywords=lg+dryer+side+vent+kit&qid=1696870524&sr=8-3