The maximum developed length of a clothes dryer exhaust duct shall not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet for each 45-degree (0.8 rad) bend, and 5 feet for each 90-degree (1.6 rad) bend.
Some dryers can exhaust beyond 25 equivalent feet without a booster fan. Dryer Duct Booster Saves significant energy - reduces drying times 50% or more. Reduces lint build-up, dust & fire hazards by maintaining proper velocity in duct runs up to 150 equivalent feet.
The International Association of Certified Home Inspectors (InterNACHI) establishes length requirements for dryer vents. The length cannot be more than 25-feet; it should also be as straight as possible. If there is a 90-degree angle in the vent, then it shouldn't be more than 20-feet.
M1502.
According to the M1502. 5 code, the construction of a dryer duct has to be a minimum of 0.4 mm thick with a smooth interior. This means ribbed vents are no longer being used. Additionally, all duct joints must point in the direction of airflow.
Too long of a vent puts extra strain on the dryer. It's also a safety hazard because the reduced airflow can allow lint to build up in the pipe.
The maximum developed length of a clothes dryer exhaust duct shall not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet for each 45-degree (0.8 rad) bend, and 5 feet for each 90-degree (1.6 rad) bend.
For most dryer models, you can't run the exhaust duct more than 25 feet from the dryer to the exhaust port. Ducts should be as short and straight as possible to reduce lint buildup. Read on to learn more about the nuances of correctly venting a dryer so you can get your laundry dry and keep you and your family safe.
Per the requirements of the International Residential Code, Section M1502 (2009-2021 IRC), the clothes dryer exhaust duct should be a rigid or semi-rigid metal duct made of galvanized steel or galvanized aluminum with a smooth interior finish and a duct diameter of 4 inches.
Dryer venting tips and practices
All dryer ducting must be a minimum of 4" in diameter. Clean, unobstructed, frictionless ducts encourage air flow efficiency, quickens drying times, adds longevity to clothing's life and reduces utility bills.
Route the dryer vent horizontally to the home's outside wall. Duct work should pitch 1/4-inch per foot to the outside. This keeps moisture out of the pipe. For basement laundry areas where your ductwork will run vertically to the outside wall, you may need to use 90-degree elbows.
Long vertical runs can result in greater humidity and lint accumulation, which will reduce drying efficiency. Vertical runs may require the installation of a booster fan to maintain effective exhaust air flow.
Here's a quick rundown: If you can't vent your dryer outside, there's a risk of fires due to lint buildup, a chance for mold to grow, your laundry room might get too hot, and drying times could increase, possibly causing damage to your clothes and higher energy bills.
DO NOT terminate dryer vents in crawl spaces or attics. Dryer vents that terminate in crawl spaces or attics allow for moisture to deposit and encourage mold growth and health hazards. Dryer vents must terminate outside of the building.
Dryer cords are usually a maximum of six-feet-long as the code requires that an outlet be close to the connected appliance. Check to see if you need a 3-prong vs. 4-prong dryer cord and take that into consideration when shopping for new appliances.
Venting a dryer through the roof is possible, but there are important considerations to remember. This method can be practical when sidewall venting isn't an option due to your building's layout. However, overall, sidewall venting is considered the safer option.
The maximum length of a 4-inch (102 mm) diameter exhaust vent shall not exceed 35 feet (7620 mm) from the dryer location to wall or roof termination, and shall terminate with a full opening exhaust hood. A reduction in maximum length of 2.5 feet for each 45-degree bend and 5 feet for each 90-degree bend shall apply.
You can use a 4-inch flexible aluminum foil duct that is UL 2158A listed and marked for safe dryer venting. Look for a product that is constructed from heavy duty, fire resistant aluminum foil with a high density, corrosion resistant wire helix. Remember that only ducts 8 feet or less can be UL listed and marked.
Reducers like 4″ to 3″ will cause a 25% or more reduction in airflow and increase the cost of operations. PVC can build up a static discharge and ignite the lint, causing a fire! Long Ductwork will reduce airflow and cause long dryer times.
Here's the brief: A dryer vent can typically run up to 25 feet for electric dryers and around 35 feet for gas dryers, with adjustments for bends and turns along the venting system. Always check your dryer's manual for specific recommendations.
In situations where outdoor venting is not an available option, the vent bucket serves as an efficient indoor solution. It collects lint and moisture, ensuring they do not disperse throughout your living area. It is particularly convenient for apartments or temporary setups.
Dry Vent Rules
Any dry vent must rise at least 6 in. vertically above the flood rim of the fixture before turning horizontally or connecting to a vertical vent pipe. The horizontal run must be sloped to allow any condensation that forms within the pipe to run back to the drain.
Flexible duct collects lint.
The typical maximum-allowable duct run for dryers is 25 ft.; anything longer than that requires a booster fan.
conditions should be at least 1,200 FPM (feet per minute) to keep lint moving through the vent. (In a 4" (102 mm) diameter pipe, this requires at least 105 CFM of air flow.) Back pressure should be measured with an empty dryer, a clean lint screen and with the dryer operating in the Air Only cycle (no heat).
High Concentrations of Carbon Monoxide
Gas dryers, without proper venting, are also capable of filling the home with carbon monoxide gas. As the gas leaves the exhausts of the dryer, it becomes concentrated indoors and can potentially poison the inhabitants of your home.