Florida Dryer Vent Code: A Homeowner's Guide
Under the Florida Building Code, a home dryer vent must be smooth 4-inch metal duct that ends outside with a damper and no screen. A standard run is limited to 35 feet, minus 5 feet for each 90° elbow and 2.5 feet for each 45°, unless the dryer maker allows more. The hose behind the dryer must be a single listed length of 8 feet or less, never hidden in a wall. Since the 2023 edition, ordinary household booster fans aren't allowed.
About this guide
This is a plain-English summary of the dryer exhaust rules in the Florida Building Code, Residential (Section M1502), which is based on the International Residential Code. It's meant to help you understand your own vent. Your local building department has the final word, and your dryer's installation instructions can change some limits.
Duct material and size
- Metal, smooth inside. The duct must be metal at least 0.0157 inch thick (No. 28 gauge), with a smooth interior. Ribbed foil or plastic flex duct isn't allowed as the main run.
- 4 inches. The duct is 4 inches nominal diameter.
- Its own system. The dryer exhaust can't be tied into a bathroom fan, range hood or any other exhaust.
The 35-foot length limit
The duct can run up to 35 feet from the dryer connection to the outside cap, not counting the transition hose. Each fitting counts against that length:
| Fitting (4-inch duct) | Deduct from 35 ft |
|---|---|
| Standard 90° elbow | 5 ft |
| Standard 45° elbow | 2.5 ft |
| Smooth long-radius 90° (6-inch radius) | 1 ft 9 in |
| Smooth long-radius 45° (6-inch radius) | 1 ft |
Example: a run with two standard 90° elbows can be at most 25 feet long. If the dryer manufacturer's instructions allow a longer run, those apply, and a run longer than 35 equivalent feet must be marked on a permanent label within 6 feet of the dryer connection.
Runs over the limit clog again quickly no matter how often they're cleaned. The fix is a shorter route. See dryer vent rerouting.
The hose behind the dryer
- One single length, listed and labeled to UL 2158A for dryer transition ducts.
- No longer than 8 feet.
- Never concealed inside a wall, floor or ceiling.
White vinyl hose doesn't meet this, and most thin foil hose isn't listed. See transition hose replacement.
Where the vent ends
- Outside the building. Never into an attic, crawl space, soffit, garage or under the house.
- At least 3 feet from openings into the building, such as windows, doors and ventilated soffits, unless the dryer maker specifies otherwise.
- With a backdraft damper, the flap that closes when the dryer stops.
- No screen. Screens trap lint and aren't allowed at the termination.
See dryer vent cap replacement.
Joints, fasteners and supports
- Each section's male end points in the direction of airflow, so lint slides past joints instead of catching on them.
- Joints are sealed and mechanically fastened. Screws can't stick more than 1/8 inch into the duct, where they would catch lint.
- The duct is supported at least every 12 feet and secured in place, so it doesn't sag.
Booster fans: the 2023 change
The 2023 Florida Building Code added a rule (M1502.4.8) that domestic booster fans shall not be installed in dryer exhaust systems. The right fix for a run that's too long is a shorter route. If you already have a fan, keep it clean and make sure its shut-off switch works, and ask about rerouting.
What we find most in Pinellas homes
- Foil or vinyl hose running inside walls or ceilings.
- Vents that end in the attic, a soffit or the garage.
- Bathroom-fan caps or screens on dryer exhausts, especially on roofs.
- Runs well over the length limit after a laundry room was moved.
- Screws through the duct, and sections joined backwards.
- Post-storm rebuilds that reused old foil duct.
Worried about your vent? A dryer vent inspection gives you airflow numbers and photos in writing.
Want it done for you?
Same-day dryer vent service across Pinellas County. Standard cleaning from $99, airflow tested before and after, price before any extra work.
Clearwater team
1727 Coachman Plaza Dr
(727) 454-0061
Clearwater area
Largo team
13801 Walsingham Rd
(727) 662-5045
Largo area
Seminole team
7821 Seminole Blvd
(727) 855-3490
Seminole area
Questions
How long can a dryer vent be in Florida?
35 feet for a standard 4-inch duct, minus 5 feet for each standard 90° elbow and 2.5 feet for each 45°, unless the dryer manufacturer allows more.
Can a dryer vent go through the roof?
Yes, as long as it ends outside with a proper dryer cap that has a damper and no screen, and stays within the length limit.
Are dryer booster fans allowed in Florida?
The 2023 Florida Building Code says domestic booster fans shall not be installed in dryer exhaust systems. Shortening the run is the fix.
Is foil dryer duct allowed?
Not for the main duct, which must be smooth metal. The short hose behind the dryer must be a single listed transition duct, 8 feet or less, and never hidden in a wall.
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