Last Updated on October 4, 2026 by Umar Farooq
A dryer vent hose replacement is a twenty-minute job with one decision that matters: buy a listed metal duct, not a plastic one. The hose behind the dryer must be a single length, no more than 8 feet, metal, clamped at both ends, and never buried in the wall — and the white flexible plastic version sold alongside it is no longer approved for the job at all.
That last sentence is the whole reason this page exists. The wrong duct sits on the shelf next to the right one, at a lower price, with a picture of a dryer on the packet.
Which duct material is permitted, and which is sold anyway
The rule is written in two places and they agree. The residential code requires that “Exhaust ducts shall have a smooth interior finish and shall be constructed of metal not less than 0.0157 inch (0.3950 mm) in thickness (No. 28 gage),” with the duct “4 inches (102 mm) nominal in diameter” (2021 Residential Code, M1502.4.1).
GE Appliances states the same thing from the manufacturer’s side, and is blunter about what changed: “Any Dryer ducting used must be UL-listed. UL now requires that all Dryers be installed with either rigid or flexible metal ducting. Rigid is preferred.” On plastic it is unambiguous — “Plastic duct work is no longer approved for a safe installation. The white flexible plastic ducts tend to contract over time where there is a curve and allow less than a 4″ diameter at 90 degree turns. Lint tends to build up in these areas and has caused fires in some cases” (GE Appliances: installation information for exhaust ducting).
Foil is where most of the internet gets it wrong, in both directions. Foil flexible duct is not simply banned and it is not simply fine. GE’s wording: “UL-listed foil Dryer ducts are only allowed under very strict criteria. For example, foil Dryer ducts can only be used in lengths of 8 feet or less.” Semi-rigid metal gets the same ceiling — “A UL-listed semi-rigid Dryer duct can be used if the vent length is 8 feet or less.” A short, listed, labelled foil transition duct can therefore be legitimate; an unlisted one, or a long run of it inside a wall, is not.
| Material | Where it is allowed |
|---|---|
| Rigid metal, 4″ | Anywhere in the run. GE: “Rigid is preferred” |
| Semi-rigid metal | Transition only, 8 feet or less |
| Foil flexible, UL 2158A listed | Transition only, 8 feet or less, strict criteria |
| White flexible plastic / vinyl | Nowhere. “No longer approved for a safe installation” |
| Anything other than 4″ round | Nowhere. Larger ducts drop air velocity and drop lint |
NFPA’s dryer safety sheet reduces the whole table to seven words: “Rigid or flexible metal venting material should be used to sustain proper air flow and drying time” (NFPA, Clothes Dryer Safety).
The transition duct is not the same thing as the vent
This distinction decides which rules apply to the part in your hands, and almost no retail packaging explains it.
The transition duct is the short flexible piece joining the dryer’s outlet to the duct opening in the wall. The exhaust duct is everything from there to the hood outside. They are different components with different requirements, and the hose you are replacing is almost always the first one. The code is specific about it: “Transition ducts used to connect the dryer to the exhaust duct system shall be a single length that is listed and labeled in accordance with UL 2158A. Transition ducts shall be not greater than 8 feet (2438 mm) in length. Transition ducts shall not be concealed within construction.”
Three constraints in three sentences. Single length means no joining two short ones to reach. Listed and labelled means the UL 2158A marking is printed on the product, not implied by the aisle it sat in. Not concealed means it stays visible and reachable — if your flexible hose disappears into a wall or floor cavity, that is not a transition duct in the wrong place, it is the wrong component for that part of the run.
Thirty-five feet is a budget, and elbows spend it
The length rule is not a straight tape measure. It is an equivalent length, which means every bend is charged at what it costs in airflow rather than what it measures in inches.
The code sets the allowance at “35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal,” and then deducts for fittings: a 4-inch-radius mitred 90-degree elbow costs 5 feet, a mitred 45 costs 2 feet 6 inches, and a smooth 6-inch-radius 90 costs only 1 foot 9 inches. The same corner, at three different prices, depending purely on how the bend is shaped.
Manufacturers quantify the same effect with their own numbers, and they do not match the code. Samsung states a flat deduction: “Every 90 degree turn reduces the maximum length by 6 feet” (Samsung: clothes are not dry after using Samsung dryer). Maytag hedges — “Many dryers perform best with total equivalent vent lengths under 35 feet; each 90-degree elbow adds resistance” — and sets no limit at all. The code says 5 feet, Samsung says 6, Maytag declines. There is no single industry figure here, so use the one in your own dryer’s installation instructions — the code itself defers to them, and only falls back on its own table “in the absence of fitting equivalent length calculations from the clothes dryer manufacturer.”
What this means in practice: if the run is tight, the cheapest airflow you will ever buy is swapping two mitred elbows for swept ones, before you touch anything else.
Dryer vent hose replacement, done in the right order
Unplug the dryer at the wall before you start. On a gas model, close the shut-off valve in the supply line as well. Let the machine cool. Do not reconnect the gas until the duct is finished and clamped.
- Measure before you buy. Pull the dryer out far enough to see both connection points and measure the straight-line distance, plus enough slack to push the machine back without folding the hose. Buy that length, not the 8-foot one because it cost the same.
- Undo the old clamps and keep them if they are sound. Most are a worm-drive band with a screwdriver slot. Cut the old duct away rather than fighting it off.
- Clear the lint from both openings. The dryer’s outlet collar and the wall opening both hold a ring of packed lint that would otherwise go straight into the new hose. Look down the wall duct while you are there — if it is furred, do how to clean a dryer vent now rather than in six months.
- Fit the new duct with the male end pointing downstream. The code states it plainly: “The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow.” Get this backwards and every joint presents a lip facing into the airstream, which is a lint hook with a long and patient career ahead of it.
- Clamp both ends. Do not use screws through the duct. The code limits fasteners to those that “protrude more than 1/8 inch (3.2 mm) into the inside of the duct” — anything deeper catches lint exactly where you cannot see it. Band clamps hold without entering the airway. Foil tape over a clamped joint is fine; tape on its own is not a mechanical fastening.
- Push the dryer back gently and look behind it. Leave the duct curved, not folded. Samsung’s two-part test for a finished run is the one worth copying: “Free from kinks or flattening. The vent should be completely open the whole way through.”
- Run a cycle and go outside. You should feel a steady push of warm air at the hood, and the flap should open. If it does not, the restriction is in the duct run rather than the hose you just replaced.
Five things the code says not to do behind a dryer
These are prohibitions rather than preferences, and each one exists because of a failure that has already happened somewhere.
- No screen or grid at the outlet. “Screens shall not be installed at the duct termination.” GE repeats it: “Never install a screen or grid of any kind in or over the exhaust duct. This could cause lint build up.” A backdraft damper is required instead, and the flap does the animal-exclusion job a screen was supposed to.
- No booster fan. “Domestic booster fans shall not be installed in dryer exhaust systems.” GE agrees: a booster or power ventilator “cannot be used or placed on an individual Dryer’s vent exhaust to boost airflow. It is not approved.” A long run gets shortened, not assisted.
- No concealed transition duct. The flexible piece stays visible. If it has to vanish into construction, that section needs rigid metal.
- No shared or indoor termination. GE: “do not terminate the exhaust into a chimney, under an enclosed house floor (crawl space), a common duct with kitchen exhaust or into an attic.”
- No larger-diameter “upgrade.” GE: “We do not allow anything other than a 4″ round duct. Larger ducts reduce the air velocity and increase the opportunity for lint to ‘fall out’ of the airstream.”
If the section needing replacement is inside a wall, through a ceiling, or longer than you can reach, get a quote instead — dryer vent cleaning cost covers what that work is priced at.
FAQ
How often should a dryer vent hose be replaced?
There is no published interval, because a listed metal duct in a straight, uncrushed run does not wear out. Replace on condition: crushed, kinked, split, detached, rusted through, or plastic.
Is foil dryer vent hose safe?
Only if it is UL 2158A listed, used as the transition duct, 8 feet or less, in a single length, and left visible. Those conditions do most of the work in that sentence. Unlisted foil, or foil inside a wall, is not an approved installation.
How long can a dryer vent hose be?
The flexible transition duct is capped at 8 feet. The rigid exhaust duct beyond it gets 35 feet of equivalent length, reduced by every fitting. Your dryer’s own installation instructions override both.
Can I use duct tape on a dryer vent?
Not as the joint. The code requires joints to be sealed and mechanically fastened, which means a clamp. Foil tape over a clamped joint is a reasonable extra; cloth duct tape dries out and lets go.
Do I need a clamp at both ends?
Yes. A duct clamped only at the dryer end works loose at the wall, and a disconnected duct discharges warm, wet, lint-laden air into the cavity behind the machine. That is a moisture problem as well as a fire one.
Will a new hose fix long drying times?
Only if the old one was the restriction. If it was crushed or plastic, expect a real improvement. If it was fine, the cause is further along the path — dryer taking too long to dry goes through the rest in order.
Rigid metal, short run, two clamps
Three things, if nothing else: buy metal, keep the flexible section under 8 feet and visible, and clamp both ends with the male end facing the way the air goes. That is most of what separates a compliant installation from the one already behind the machine.
And if the duct you are pulling out is white plastic, do not reuse it anywhere, not even temporarily. It is the one material in this whole job that every source agrees on.
