Last Updated on October 6, 2026 by Umar Farooq
A dryer vent wall cap is the hood where the duct leaves the building, and its only two jobs are to let exhaust out freely and keep weather, wind and wildlife from coming back in. It must have a backdraft damper, and it must not have a screen — the residential code says so in the same sentence. That second half is where most of the bad advice on this subject lives.
This part matters more than its size suggests because it is the one component in the vent system nobody looks at. The lint screen gets cleaned every load; the duct gets a mention once a year; the cap sits eight feet up an outside wall behind a shrub, and the first anyone knows about it is a cycle that will not finish or a stain spreading down the cladding.
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What a dryer vent wall cap is actually doing out there
Air leaves your dryer warm, wet and carrying whatever the lint screen missed. It arrives at the cap, pushes a flap open, and exits. When the cycle stops the flap has to fall shut, not for comfort but because an open hole in a wall is an invitation: cold air comes back down the duct and condenses, lint settles where the airflow stopped, and birds find a round cavity at about the diameter they were looking for with a door that swings inward under almost no pressure.
So the cap does three contradictory things at once — opening under very little pressure, closing reliably when the pressure stops, resisting anything pushing the wrong way. Every design in the category trades between those three, and the cheap ones resolve it badly.
The code sets the floor. “Exhaust ducts shall terminate on the outside of the building”, terminations are made to the manufacturer’s instructions, and where those are silent “the exhaust duct shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings” (clothes dryer exhaust, M1502.3, as adopted in Colorado). That three-foot clearance is the check nobody runs. Go and look at where your cap sits relative to the nearest window, soffit vent or fresh-air intake, because no hood fixes a hole in the wrong place.
The flap: one wide gravity damper beats four small louvres
This is the specification that decides whether your cap still works in three years, and it is almost never described properly in a product listing.
A single wide gravity flap on a hooded cap handles the contradiction best. It is one hinged plate as wide as the duct, lifting on the airflow — large enough to need very little pressure to move, heavy enough to fall fully shut, with the hood above keeping rain off it.
A spring-loaded damper closes harder, which is better against wind-driven rain and against something trying to lever it open. The cost is that the dryer pushes against that spring every cycle, which is pressure out of a system that may not have much spare.
Four small plastic louvres are the version sold in multipacks and fitted by builders. Each one is light enough to flutter and small enough to jam. Lint builds along the bottom edge of each, and once one is half stuck the others carry its share of the flow and stick too. This is the style usually responsible when somebody says their cap has stopped opening.
Screens are banned at the termination, and the code says it plainly
Here is the costly myth, and it is costly because the product that causes it is sold as a feature.
The same code sentence that requires the damper forbids the screen: “Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.” Not “screens should be fine mesh”. Not “with caution”. Shall not.
The mechanism is obvious once you have seen one. Lint is fibrous and arrives warm and slightly damp. Any mesh across the opening is a felt-making machine: the first fibres bridge the gaps, the next catch on those, and within months there is a mat you cannot see from the ground choking the one point in the system where air is supposed to be free. That is the failure behind the smell GE describes — “If this odor is noticeable on installed Dryers, check the venting for possible build up of lint. A lint build up odor may emit a burning smell or musty scent” (GE Appliances, contentId 18962) — and NFPA’s research attributes about a third of home dryer fires to a failure to clean, with 27 percent igniting in dust, fibre or lint.
Which leaves the genuine problem the screen was trying to solve. Birds do nest in dryer vents, because the duct is the right diameter and the damper is the easiest door in the building. The allowed answers are a heavier damper a bird cannot lever open, a hood that makes the approach awkward, and a wide guard bar rather than mesh. Several caps ship with a removable bird screen, and removable is the only acceptable form of the thing: take it out before you fit the cap, and keep it in the drawer with the manual.
Discoloured siding, frost and the other tells that yours is leaking
No manufacturer publishes a diagnostic chart for this, so treat what follows as mechanism and observation rather than cited specification — but it is what to look at.
A stain fanning down or sideways from the hood. The exhaust is warm and humid. Escaping around the collar instead of out through the flap, it condenses on cold cladding and whatever fibre it carries sticks to the wet patch. Over two winters that reads as a grey or brown smear whose shape points back at the leak.
Frost around the hood in cold weather and nowhere else on the wall. Same cause, different season: moist air reaching the outside of the cap instead of being thrown clear of it.
A flap open when nothing is running. Jammed with lint, nested behind, or a corroded hinge. Maytag’s instruction takes ten seconds: “Outside, confirm the vent hood flap opens freely during operation and clear any lint, debris, or nests” (Maytag Product Help).
A rattle in the wind. A flap that has lost its stop, or a spring that has gone. Harmless, annoying, and a sign the cap is finished.
If the flap is not moving at all while the dryer runs, the cap may be innocent — a blockage further up the duct reduces the pressure arriving at it. How to clean a dryer vent has the airflow test, and if drying times are the real complaint, dryer taking too long to dry ranks the five places restriction actually occurs.
Material, size and the hole you already have
Duct diameter, not wall opening. Residential dryer duct is 4 inches — GE’s wording is “we recommend the use of a solid metal vent pipe 4″ in diameter for adequate operation” — and the collar has to match it. A 6-inch cap on a 4-inch duct leaves a step where air slows and lint settles. Measure the pipe, not the hole in the siding.
Collar length. The spigot behind the cap has to reach through siding, sheathing and insulation to meet the duct. A short collar on a deep wall gets bridged with tape, and tape is what fails and produces the stain.
Material. Galvanized steel is the default: rigid, cheap to make heavy, and it carries a damper that still falls shut in ten years. Aluminium is lighter, will not rust, and comes painted white. Copper is for houses that already have copper on them. Avoid plastic on a sunny elevation — UV makes it brittle, and a brittle damper stops being a damper.
The faceplate footprint. You are covering an existing hole and probably an existing paint shadow, so measure what is there. A smaller faceplate means filling and painting.
Three caps worth fitting to a 4-inch run
FAMCO galvanized steel hooded wall vent, the default replacement
A hooded metal vent with a damper, from a manufacturer that has been making exactly this part for decades, and the top-ranked item in Amazon’s dryer replacement vents category. The specification that justifies it is weight: at around 18 pounds packaged this is a substantially heavier assembly than the stamped and plastic alternatives, and heavier is what makes a gravity damper close properly and keeps a bird from pushing it. It is bare galvanized, so to disappear it into white trim you will be painting it. Stock runs thin on this one — the same hood is also made in copper.
Old World Distributors hooded copper vent, for a house with copper on it
A 4-inch hooded copper dryer vent with a backflow damper, made from 16-ounce copper at 0.021-inch thickness and hand-built in Michigan. Buy it for one reason: the building already has copper gutters or flashing and a painted steel hood would look wrong for thirty years. The useful detail is that its bird screen is removable, which is the only form of bird screen that belongs near a dryer — fit the cap, leave the screen in the box, and you get the hood geometry without the lint mat. It will also go bright to brown to green on its own schedule, which is either the point or a problem depending on your taste.
Imperial aluminium wall exhaust hood, sold as a case of five
A painted silver-and-white aluminium hood, 16½ inches long with a 4-inch collar, from a named maker of venting components. Two reasons to choose it: the long collar reaches through a deep wall assembly without an extension joint, and the white finish means no painting on white trim. The thing to know before you click is that it is sold as a case of five, not as one — right if you own a duplex, a rental, or a house whose bath fans terminate the same way and you would rather do all of them in one afternoon, wrong if you need exactly one hood. Amazon also files it under an automotive category, which is a listing artefact rather than a description of the part.
When replacing the cap fixes nothing
If the duct behind the cap has not been cleaned, a new hood buys you a clean flap on a dirty system and the drying times will not move. Clean first, then judge the cap; dryer vent cleaning cost covers what that is worth paying for.
If the flexible transition between machine and wall is crushed, kinked or foil accordion, that is your restriction and the cap is a bystander — dryer vent hose replacement is the cheaper fix.
And if your real complaint is that something is living in the vent, the cap is half an answer. The nest has to come out before the new hood goes on, or you have sealed it in. That is a job with a ladder and, in some places, a protected-species question.
FAQ
Should a dryer vent wall cap have a screen?
No. The code requires a backdraft damper at the termination and states that screens shall not be installed there. Lint bridges any mesh and mats into a blockage at the one point in the system where airflow has to be unobstructed. If a cap arrives with a removable screen, remove it.
How do I stop birds getting into the dryer vent without a screen?
Use a heavier damper a bird cannot lever open, a hooded geometry that makes the approach awkward, or a cap with a wide guard bar rather than mesh. A nest already in place has to come out before the new cap goes on, not be sealed behind it.
What size dryer vent cap do I need?
Match the duct, which in a house is almost always 4 inches. Measure the pipe rather than the hole in the wall. A collar larger than the duct creates a step where air slows and lint settles.
How far does a dryer vent have to be from a window?
Where the dryer manufacturer gives no figure, the code requires the duct to terminate not less than 3 feet in any direction from openings into the building — windows, doors, soffit vents and fresh-air intakes included.
Why is my dryer vent flap not opening?
Either the flap is stuck, with lint on the hinge, a nest behind it or corrosion, or the pressure reaching it has dropped because the duct is blocked further back. Check the flap by hand first, because a new cap does nothing for a blocked duct.
Can I replace a dryer vent wall cap myself?
Usually yes, if you can reach it safely. It is four screws, a caulk line and a duct joint. What catches people out is collar length against wall depth, and matching the existing faceplate footprint.
Fit a damper, skip the screen, check the siding
The cap has a short specification list and all of it is physical. One wide gravity damper rather than four plastic louvres. Metal heavy enough that the damper actually falls shut. A collar matching a 4-inch duct and long enough to reach through your wall. No mesh across the opening, ever, however the listing describes it. And once a year, when the duct gets cleaned, stand outside with the dryer running and watch the flap — that is the whole inspection.
For most houses the galvanized steel hood is the right buy, because weight is what makes a gravity damper work, and that damper is the only moving part out there.
