Do Americans in dense city centers vent their dryers directly outdoors?

Question

I live in California in a normal single family home.

My normal US dryer vents out the back into a duct that eventually goes out the side of my house - it vents moisture, air and lint directly to the outdoors.

I have never considered any other method of doing this.

HOWEVER, I am visiting a European city center and the dryer here is not connected to a vent at all. Instead, there is a fairly elaborate filter in the front and in the back and inside the filter there is an actual filter insert that is quite aggressive (fine) and prevents all lint from exiting the dryer.

I suspect it is also significantly hindering the drying efficiency but who knows ...

Anyway ... it got me thinking ...

I am fairly certain that this setup is intended to prevent direct venting of lint and the accompanying air pollution that that implies. This is a very dense city center and is kept very clean and pollution free.

Which brings me to my question:

In similar, very dense city centers in the United States - say, Manhattan or central Boston - do people directly vent dryer exhaust like I do in California ? Or do they have weird setups like I see here in Europe ?

Thanks.

Answer 1

You're missing the big picture here

While your concern about lint causing pollution is at least reasonably admirable, the reason European dryers have all that filtering instead of a vent isn't for the sake of keeping lint from being an air pollutant. Instead, the reason for the extra filtration is because while standard American dryers simply heat up air drawn from the inside and blow it through the tumbling clothes, sending all that dearly paid for air out the exhaust pipe, European dryers do something much more clever, effectively using a dehumidifier to condense the moisture out of the air exhausted from the drum so that it can be recycled back into the drum. This is called a heat pump dryer, and is something that is starting to become available in North America as well (albeit only spottily).

This requires the extra lint filtration you see to prevent lint from clogging the refrigeration coil fins, but has the massive advantage of using much less power (and less energy) than a conventional electric dryer, to the point where you can have a combustion-free clothes dryer that plugs into a standard 15/20A, 120V socket. (Miele's North American market dryers do just that, even.) Furthermore, their lack of a vent has a second order impact on energy consumption: not only do they use less power and energy in and of themselves, but by not sending conditioned indoor air out the dryer vent, they reduce the parasitic load put on the building HVAC system, especially during wintertime where well-insulated buildings (think Passivhaus) can trap the heat effectively as well.

Answer 2

TLDR: Often not, due to costs or incentives.

Lint is not a significant pollutant.

The major reasons are:

• The high construction cost of building a dryer vent in every apartment.
• The enormous energy wastage of taking interior air, which is already fully conditioned for temperature and humidity, and ejecting it outside. This is exactly the same problem as "1-hose" portable air conditioners... like them, a 2-hose dryer could cure it, but who's ever seen one of those?
• The air being ejected by the dryer has to be made up somehow - exterior air must now be let into the building. Even modern American construction is tight enough that you have to actively think about that - ordinary window and door seal leaks won't provide that much leakage anymore. Having to deliberately add leakage to support That 70's Dryer is not good for efficiency.

The upshot is, the traditional American "vented dryer" is highly incompatible with a number of best practices in HVAC design and efficient buildings. They are popular because they are cheap to buy -- that is a perverse incentive for Americans to keep buying them even though they are a net financial lose!

My next paragraph would turn political, re: how governments help (or refuse to help) eliminate perverse incentives, so I'll go ahead and not say it.

How it works there (and you can get them here)

Generally these dryers boil down into two technologies.

First is called the "Condensing Dryer". This takes the hot, wet dryer air and runs it through a heat exchanger with normal room air. This cools the hot air (at the cost of heating the room) causing some of the water to condense. The air is then heated again and sent back through the dryer. Wet air is NOT intentionally dumped into the room (that would be bad).

But honestly, this is not great. Ambient room air (think 65-100°F/20-38°C, not all European homes have air conditioning) isn't all that great for cooling the heat exchanger. And obviously the heat exchanger needs to fit inside a dryer! So they are slow as daylights. So they tumble for a long time, which is bad for clothing life.

The cure for those limitations is a "Heat Pump Dryer", which is basically a common freon-based dehumidifier inside the body of a dryer. It is doing the same thing, but using a Freon engine to do the "physics cheat code" :) It efficiently makes a 2°C/35°F "cold zone" for highly efficient condensing, and a proportional "warm zone" to preheat the air being blasted through the tumbler.

These work slick as a whistle. They simply need electricity (and not that much of it thanks to those cheat codes), and a drain to dump the water (they can coat-tail the washing machine's drain in most installations). They do not need gas, and in some cases do not need 240V.

I suspect the lint filter is also significantly hindering the drying efficiency but who knows ...

Not at all. First you don't actually mean "efficiency", what you mean is "drying speed" - not the same thing at all.

The poor performance is owing to "condensing" (non-heat-pump) dryers relying on ambient room temperature to get useful condensing. That can be very adverse if the laundry room is closed in and allowed to heat up. Heat pumps solve this by using those "physics cheat codes" to mechanically make a large temperature difference. They're still not quite as fast as a vented dryer, because drying is super easy with an unlimited supply of pre-conditioned air that was paid for by an "externality".

The self-economic pressure by cheap builders

These types of dryer tend to show up in the USA with large development builders (e.g. a big condo complex) where the cheap builder seeks to reduce the cost of installing the many utilities needed in a laundry room:

• Cold water
• Hot water
• Drain
• Dryer vent
• 120V (for washer)
• 240V (for dryer)
• Gas (for dryer)

The cheap builder can whittle down utilities thusly: First, support only gas OR 240V (probably going to happen regardless). Use a washing machine with onboard water heater, that crosses off "hot water". Use certain models of washer-dryer where the washer daisy chains AC power off the dryer; 120V gone*. And as discussed, dump the dryer vent. The cheap builder has eliminated 4 utilities and are now down to 3: cold water, drain and 240V.

* eliminating 120V only works if it's a laundry alcove just big enough for the machines. If it looks like a laundry room a 120V/20A circuit is required per NEC.

The cheap builder says "I will pay more for the specialty appliances, but I save considerably more than that."

The government pressure

Governments like to promote efficiency, such as LEED buildings. As discussed, a "dryer vent pipe" is a gut-punch to HVAC efficiency. So when a builder is being incentivized, or mandated, to hit efficiency targets, eliminating the dryer vent is a "low hanging fruit". And yes, they are sometimes omitted in the most modern buildings.

Answer 3

A dryer heats air, blows it through the clothes so the air loads up on moisture, and then... you got a load of hot moist air. Oldskool dryers just dump that outside, which gets rid of the moisture and all the energy used to heat the air and evaporate the water.

So a condenser dryer uses an air/air heat exchanger to remove heat from the exhaust and transfer that heat to the air intake. That saves on heating and also causes the water to condense into liquid, so it is evacuated in the drain. There's a filter for the lint. So basically, this type of dryer cycles the same air (from the room) many times while removing the water from it. It works very well. It's supposed to be more efficient than a vent dryer, but... it depends. It does use a little bit less energy, but it's not spectacular. The main advantage is you don't need a hole in the wall.

In winter, it certainly is more efficient because all the energy that was used remains in the house instead of being thrown out through the vent, so you get "free" heating. Well, it's not free, because you pay for the electricity, but at least you get to keep the heat. In summer, it's the same, except you really don't want to keep the heat.

Then there's heat pump dryers. It's the same principle, except a heat pump recovers heat from the hot exhaust, which cools it and condenses the water, then it dumps the heat back into the air which is now dry. It's exactly like a compressor dehumidifier. And it runs in closed circuit (still with some room air). Since it's a heat pump, it'll have a COP>1 so you can expect to pay 2-3x less electricity, but the machine is a bit more expensive.

Answer 4

I randomly picked a current Whirlpool model and checked the installation. Very clearly states that it must be vented to the outside, no ifs, ands or buts. There may be some models that are designed for inside venting through a filter, etc. but that is certainly not the normal setup in the US.

There are 3 issues with venting dryers:

• Lint - This can be mitigated, at least in theory, with a filter to catch the lint. In fact, every dryer includes a filter that catches most of the lint. But even a small amount of lint can cause problems (fire hazards, health hazard) and that is far worse inside than outside.
• Humidity - This is a big problem and can't be solved without a total redesign. That redesign is known as a condensing dryer or a ventless dryer.
• Combustion Products - This is a concern only for gas, but is a real safety issue because incomplete combustion produces carbon monoxide, which is deadly.

So the solution is a ventless, condensing dryer. But that's new technology, costs more (and will always cost more than vented dryers, unless vented dryers are outlawed, simply because the technology is much more complex than vented dryers - vented dryers are little more than heat source + motor/pulley/belt/drum + fan) and can take longer to dry.

What are you finding in Europe? Could be any combination of condensing dryers (i.e., designed to vent inside, a.k.a. ventless), electric dryers (hopefully not gas!) simply being used improperly (my house came with a dryer set up that way, but I moved it many years ago to vent outside) or some other technology. But unless/until US jurisdictions require a change, most people will continue to install traditional vented dryers because they are cheaper (at least in the short run - in a quick search, vented start at around $600, ventless start over $1,000; condensing may be cheaper in the long run once energy costs are included).