Dryer Vent Code and Requirements in Florida: Duct Type, Length, and Hood Rules
Most dryer vent problems are not caused by lint alone. They start with how the vent was installed. Here is a plain-English look at the rules that generally apply to dryer exhaust ducts, and the installation mistakes we run into most often.
Why Dryer Vent Rules Exist
A dryer pushes a lot of hot, moist, lint-filled air through the duct. If that duct is the wrong material, too long, or full of bends, lint collects and airflow drops. The rules are there to keep that air moving and to keep the lint from becoming a fire hazard. Our Dryer Vent Fire Safety page explains what is at stake when airflow is restricted.
The Main Rules at a Glance
| Topic | What Is Generally Expected |
|---|---|
| Duct material | Smooth-walled metal duct, not plastic or vinyl, and not thin foil or accordion-style duct hidden inside walls |
| Duct size | Typically 4 inches in diameter, unless the dryer manual says otherwise |
| Short connector (transition duct) | A short, listed flexible metal connector between the dryer and the wall duct, kept to a limited length and not hidden in walls |
| Maximum length | Commonly 35 feet from the dryer to the outside, reduced for each bend, unless the manufacturer’s instructions allow a different length |
| Joints and fasteners | Joints sealed so lint can’t leak out, and no screws sticking into the duct where they would catch lint |
| Exit point | Outside the home, with a backdraft damper and no screen over the end |
| Where it must not end | Into an attic, crawlspace, garage, wall cavity, or another duct system |
Duct Material: Rigid Metal Is the Standard
Rigid metal duct has a smooth inside surface, which lets lint slide through instead of catching. Flexible foil or vinyl duct has ridges that trap lint, and it can sag, crush, or tear. Plastic and vinyl are also not made to handle the heat a dryer produces. If you can see a ribbed, accordion-style duct running through a wall or ceiling, that is usually a sign the installation should be looked at.
A short length of flexible metal connector is sometimes used behind the dryer so the machine can be pushed back against the wall. That is generally fine as a short link, but it should not be the main duct run.
Length and Bends: Where Airflow Gets Lost
Every foot of duct and every bend slows the air down. That is why model codes commonly set a maximum length and subtract an allowance for each elbow. A 90-degree bend typically counts for around 5 feet, and a 45-degree bend for less. For example, a 25-foot run with three 90-degree elbows could be treated as roughly 40 feet, which is already past the usual 35-foot limit.
Many dryer manuals set their own limits, and some are shorter. A long or twisty run does not mean the vent is illegal, but it does mean it will clog faster and need cleaning more often. Our cleaning frequency guide explains how to adjust the schedule for long or complicated runs.
The Exterior Hood
The vent should end outside, with a hood that has a flap (a backdraft damper) that opens when the dryer runs and closes when it stops. That flap keeps outside air, pests, and rain out. Two things we see often go wrong here: a screen or mesh covering the opening, which catches lint and clogs quickly, and a hood that has been painted shut or has a stuck flap. Coastal salt air makes stuck flaps more common in St. Augustine, and our guide to birds, pests, and nests covers what happens when animals move in.
Common Installation Problems We See in St. Augustine
- Foil or vinyl duct used for the whole run instead of rigid metal
- Screens over the hood that clog with lint
- Screws through the duct that catch lint and build up into a clog
- Venting into an attic, crawlspace, or soffit instead of directly outside, which puts hot, damp, lint-filled air where it should not be
- Crushed or kinked duct behind the dryer where the machine was pushed back too far
- Very long runs with several bends, especially in older homes or after a renovation (see our note on renovating or remodeling)
If your vent has any of these, cleaning helps, but it won’t fix the underlying installation. That is when repair or replacement makes sense.
Does an Older Home Have to Meet Today’s Code?
Generally, homes aren’t required to be rebuilt every time the code changes. But when a new dryer vent is installed or the duct is substantially altered, the work is usually expected to meet the current rules. Whether a permit is needed for your project depends on the scope, so it is worth asking the local building department before starting. Even where an old vent is not required to be updated, replacing a thin foil duct with rigid metal is often a worthwhile safety upgrade.
Frequently Asked Questions
Can I use flexible foil duct if the run is short?
A short, listed flexible metal connector behind the dryer is common. Using ribbed foil or vinyl duct for the main run, especially inside a wall or ceiling, is not recommended because lint catches in the ridges and the duct can crush easily.
How do I know how long my vent run is?
Measure the duct from the dryer connection to the outside, and count each bend. If you can’t see the whole run, a professional can check it during an inspection and tell you whether it is likely to cause airflow problems.
Do you do code inspections?
No. We clean and inspect dryer vents for airflow and condition, and we point out problems we find. We are not building inspectors, so questions about permits and what your local code requires should go to your building department.
Not Sure If Your Vent Is Installed Right?
A quick inspection shows the duct type, the hood, and how the airflow is, so you know where you stand.