Clothes dryer exhaust vent termination at walls or rooftops:

Clothes dryer vents should terminate outdoors and should be screened enough to prevent entry by animals as well as to minimize cold back-drafting when the dryer is not in operation.

This article describes problems with lint-clogging at the dryer vent screen and suggests regular inspection & cleaning and perhaps installation of clog-resistant dryer vent terminating devices that reduce lint clogging. (They do not completely prevent lint clogging.)

At the top of this page: a sidewalk-level commercial dryer vent in San Miguel de Allende, Guanajuato. This dryer vent is not so easy to clean and is clog-prone.

This article series describes good practices for clothes dryer vent installation, lint traps, wall vents, filters, and screens. We include a list of clothes dryer fire safety hazards and other clothes dryer installation or maintenance mistakes that are either unsafe or that interfere with effective, economical dryer operation. We discuss types of dryer vent ducting and dryer vent doors or opening protection devices

Clothes Dryer Exterior Wall Termination, Covers, Shields & Rooftop Dryer Vent Warnings

Standard or typical clothes dryer wall vents like the angled vent hood shown above have a hinged flapper door that is opened by the pressure of the dryer exhaust air.

Watch out: do not use a wall vent hood that uses a magnetic catch to hold the flapper door from opening.

Magnetic-latched vent hoods may be sold to resist wind uplift and drafts but in a clothes dryer application they're dangerous as the flapper may not open when it should, risking a clothes dryer fire.

Our sketch below shows three types of dryer exhaust vent hoods: from left to right,

• angled hood - a single round hinged flapper door opened by dryer air pressure
• box, hood - operating the same as the angled hood
• louvered hood - with multiple hinged horizontal louvers that are intended to open in response to dryer air pressure

All three of these dryer exhaust vent hoods or wall termination covers appear in a Whirlpool dryer manual as recommended exhaust hood styles.

Animal Entry Risks at Bathroom Vents & Clothes Dryer Vents

Photo: a rusted, inoperative bath or dryer vent termination in the gable end wall of a Poughkeepsie NY home.

This vent has lost its closing cover, is badly rusted, and in windy rainy conditions the vent may also be leaking into the home's exterior wall.

Watch out: In addition to the unpleasant dose of cold air that may be blowing onto people stepping out of a shower (if this is a bath vent), the opening is an invitation to birds or squirrels to nest in the vent, blocking it.

The results of a blocked bath vent are indoor moisture problems and potentially biological hazards, depending on just who built their nest inside the vent or vent duct.

The results of a blocked clothes dryer vent can be more immediately dangerous, risking clothes dryer overheating and a building fire.

Below:

Here is a closer look at this antique, dysfunctional and leaky exhaust vent termination cover.

Louvered-dryer vent clog risks

Below are three types of dryer vent termination hoods.

OPINION: Watch out: we have found serious and chronic lint clogging of louvered dryer exhaust vent hoods IF the hood uses multiple louvers that are small in width. At page top I show an "always open" louvered dryer exhaust vent screen blowing lint onto a sidewalk in San Miguel de Allende.

This is a commercial laundromat facing heavy dryer usage. I have, on occasion seen this opening totally blocked by lint.

Shown at the right side of the sketch (colored orange for identification) is a louvered dryer vent hood sporting six hinged horizontal louvers - a design I think is clog prone.

On the other hand, a louvered vent hood with just two or perhaps three flapper vanes (as I will illustrate below) is in my experience less prone to lint clogging, probably because when the dryer is running and the louvers open the free opening space is larger.

Exterior wall clothes dryer vent termination clogging check

Check the exterior wall dryer vent screen monthly for lint blockage.

Lint blockage and clogging often occurs right at this screen, causing longer dryer operating times and possibly overheating.

Watch out: In addition to lint clogging, some dryer vent terminations and covers, particularly those that rely on a flapper that is opened by the moving exhaust air, can become stuck in the open position, inviting dangerous vent line clogging by entering birds or insects.

Such vents may continue to pass dryer exhaust but you'll notice that when the dryer is off the flapper is not closed.

That's a clue that the vent needs more-frequent inspection and cleaning.

Our clothes dryer vent photos below illustrate lint clogging at an exterior dryer wall vent after six months' of usage.

Screens over the dryer exhaust vent clog quickly and are prohibited in many jurisdictions.

These pictures show why it is so important to inspect and clear lint from the dryer wall vent at least every few months.

Because this was a brand new dryer vent installation, the rate of dryer vent system lint accumulation is unambiguous.

The laundry and clothes dryer system in this home was used by a family of four, including two young children for a period of just six months.

Below we illustrate our inspection of the interior of this six-month-old laundry dryer vent duct system.

We removed the outer screen on this vent as that would allow more lint to blow freely to the outdoors and would slow the system clogging rate. The screen was unsafe.

Below I'm inspecting the vent termination louvers for free movement.

Watch out: like the dryer vent termination snafu shown below (this is from a different building), do not leave off the dryer wall vent hinged, louvered-rodent cover itself: doing so invites birds or rodents to nest in the duct system, leading to unsanitary conditions, vent blockage, and fire risk.

Below I'm showing the plastic screen that was sold with this two-louvered dryer vent termination cover. (We did not re-install this screen.)

Above: I am removing the plastic screen and below I've opened the hinged louvers to show the view of the interior of the dryer exhaust duct.

Above you can see six months of lint accumulation - rather light - in a brand new, solid metal 4" clothes dryer vent system that began with no blockage but that apparently was not checked nor cleaned during six months of use.

Below: We inspected this dryer exhaust vent terminal covering with the dryer running on a chilly night, giving a good view of the freely-opening louvers as well as a large billowing cloud of moisture condensing from the hot humid dryer exhaust air.

Rooftop Clothes Dryer Vents Also Clog & May Be Blocked by Snow or Ice

Our photos just above and below illustrate our investigation of a lint-clogged rooftop clothes dryer vent located on a low slope roof in New York. Below you see years of lint accumulation in the dryer vent duct on this home.

This 20+ year old clothes dryer vent system had become totally blocked with lint (a fire hazard as discuss below) and of course the cost to operate the clothes dryer was multiplied by the long run-time necessary because there was no functional exhaust of hot moist air.

A symptom of the trouble was that the owners noticed that the clothes dryer was really hot at the end of a dryer cycle.

Equally poor design of this clothes dryer vent system was its installation on a nearly flat roof in a climate where winter snow cover could completely cover and block the vent even if its internal ducting were not already clogged by lint.

Below: the same roof where this clothes dryer vent is installed is shown covered in nearly a meter of snow.

No clothes dryer can melt its way through so much deep snow: the dryer vent will be initially blocked by snow, and when the dryer is operated the result may be a rooftop clothes dryer vent that is further blocked by ice from melted snow or even a dryer vent that blocks open and allows melting snow to enter the building.

This rooftop dryer vent design is more likely to cause a dryer fire than to put out the fire by melting rooftop snow.

Watch out: as you can see above, such deep snow will completely block a rooftop clothes dryer exhaust vent.

Air-Operated Exterior Clothes Dryer Wall Vents Avoid Lint Clogging

This topic has moved to its own home page

at CLOTHES DRYER LINT CLOG RESISTANT SCREENS

Fire Hazards from Clogged or Improperly-Installed Clothes Dryer Vents

This discussion moved to a separate page:

CLOTHES DRYER FIRE HAZARD WARNINGS where we include more photos of blocked dryer vents and ducts.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2018-06-30 - by (mod) - Unsafe dryer vent: at ground, lint-clogging screen, dead mice

Kevin

Thanks for your comment, we agree, and go further explaining the fire hazard involved when a too-small-opening screen covers the dryer vent exhaust opening.

Nevertheless, people will continue to either buy these covers or make their own.

Last winter at a home in Two Harbors Minnesota I saw a do-it-yourself dryer exhaust vent screen made out of hardware cloth (wire with small square openings) that the homeowner or her children had installed "to keep mice out of the dryer vent".

It was totally blocked by lint and the dryer was taking a really long time to dry clothing.

The family didn't notice the long dryer time and I figured nobody looks at the dyer vent for clogging.

I pulled off the screen and FOUR dead mice fell out of the vent. The screen was blocking lint but not blocking the mice!

I was wrong on every count.

The homeowner told me that she inspects the screen for lint clogging from time to time but had forgotten to do so.

At my next site visit in the spring, the family had put the vent screen back in place - or made a new one - and it, too, was totally clogged again.

My photo above shows the dryer vent screen as-found and the next photo I'll post is of the mouse corpses that fell out of the vent when I removed the clogged wire screening.

Here are the dead mice - or some of them that were recognizable as mice - when I pulled off the lint-clogged screen

And here you and other readers can see how clogged this dryer vent screen becomes - quickly.

We won't discuss the worry of the dryer vent becoming blocked by snow.

Watch out: the sharp edges of this metal lath used as a home-made dryer vent screen add the risk of a nasty cut when trying to remove, install, or clean the screen. Worse-still, as the vent and screen are a winter mouse hotel, a cut on this lath bears the added risk of infection.

A clothes dryer that senses unsafe temperatures and shuts off improves building safety and is a feature included in new appliances but is not found on older ones.

See details at

CLOTHES DRYER VENT CLEARANCES & TERMINATION - distance to ground & to other features

CLOTHES DRYER TEMPERATURES

On 2018-06-29 by Kevin H. - bird stopping covers over dryer vent exhaust covers are against the mechanical code

Those rodent and bird stopping covers over dryer vent exhaust covers are against the mechanical code (and residential code) in most states (see the International Mechanical Code, aka the IMC from ICC).

There is no UL listing for such covers, and highly doubtful there will ever be one, as the lint can become trapped into the webbing of whatever material the cover is made of.

On 2016-11-20 by Casey - birds getting into the dryer vent

I am renting a duplex home and the dryer duct that vents to the outdoors. Initially it didnt have any covering and birds were getting into the vent. I said something to the landlord because the dryer also was taking way too long to dry a load.

Maintenance staff say their wasn't a build up of lint in the outdoor vent. Then they installed a plastic screen over the vent but never installed a back draft damper.

The vent also vents right above the back patio storage area where there is a small roof covering the back patio storage area. They put these plastic screens on all the outdoor vents.

From what I have read the screen is against code. Also they need to have a backdraft damper installed at the end of the dryer vent. Also is this a fire code with the vent being right above the roofing?

Also on the other vents from what I read screens are allowed. But shouldnt they have back draft dampers to prevent cold air from going into the bathroom vents?

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Continue reading at CLOTHES DRYER FIRE HAZARD WARNINGS, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see this

Article Series

• APPLIANCE DIAGNOSIS & REPAIR
• CLOTHES DRYER INSTALLATION & REPAIR - home
• CLOTHES DRYER ASBESTOS
• CLOTHES DRYER FIRE HAZARD WARNINGS
• CLOTHES DRYER FIRE RESEARCH
• CLOTHES DRYER LINT FILTER HAZARDS
• CLOTHES DRYER LINT CLOG RESISTANT SCREENS
• CLOTHES DRYER SAFETY CHECKLIST
• CLOTHES DRYER TEMPERATURES
• CLOTHES DRYER TEMPERATURE MEASUREMENTS
• CLOTHES DRYER VENTING - home
  • CLOTHES DRYER VENT BOOSTER FANS
  • CLOTHES DRYER VENT CLEARANCES & TERMINATION
  • CLOTHES DRYER VENT CODES
  • CLOTHES DRYER VENT ENERGY SAVINGS
  • CLOTHES DRYER VENT INSTALLATION
  • CLOTHES DRYER VENT TERMINATION & SCREENS
  • DRYER EXHAUST VENT DUCT MATERIAL & SIZE
  • DRYER EXHAUST VENT HOOD TYPES
  • DRYER EXHAUST VENT INSTALLATION & ELBOWS
  • DRYER EXHAUST VENT ROUTING OPTIONS
  • DRYER EXHAUST VENT MISTAKES
  • DRYER EXHAUST VENTED INTO ATTIC
  • DRYER EXHAUST VENTED THROUGH ROOF
  • DRYER EXAUST VENTED INTO CRAWL
  • DRYER INSTALLATION & OPERATION MANUALS

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INDEX to RELATED ARTICLES: ARTICLE INDEX to APPLIANCE REPAIR

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