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.
The general rule of thumb is that your dryer vent shouldn't exceed 25 feet (7.6 meters) in total length. If you have gas dryers, then, these dryers can have vents up to about 35 feet long because they have stronger fans. However, there's a catch! Every bend and turn in the vent acts like a speed bump for the airflow.
The maximum length of the exhaust duct does not include the transition duct. This means that vents should also be as straight as possible and cannot be longer than 35 feet. Any 90-degree turns in the vent reduce this 35-foot number by 5 feet, since these turns restrict airflow.
The exhaust duct should be rigid metal 4 inches in diameter and no more than 35 feet in length or as specified by the duct manufacturer. This length should be decreased by 2.5 feet for every 45-degree bend the duct makes and 5 feet for every 90-degree bend the duct makes.
The most common place to vent your dryer is horizontally through the exterior wall near the dryer, which is the ideal placement. Other common locations are through (but not into) the basement or the attic/roof.
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.
Dryer venting tips and practices
Flexible transition hose between the dryer and the wall outlet should be either the foil type or the aluminum flexible duct (most preferred). Do not use the plastic or vinyl. Concealed ducting must be rigid metal (galvanized or aluminum) duct.
A summary of the typical codes relating the dryer venting is as follows: Dryer vent systems shall be independent of all other systems and shall convey the moisture to the outdoors. Terminations shall be a minimum of three feet from property line and 12" above the ground and not exhibit any type of screen.
The vent hood should have hinged dampers to prevent backdraft when the dryer is not in use. The total length of flexible metal duct must not exceed 8 ft. (2.4 m).
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.
Avoid Long Vertical Runs: If vertical runs are necessary, they should be as short as possible.
Dryer Vents should never be longer than 35 feet
The 4″ smooth metal pipe between the laundry room and the outside should never be longer than 35′. 5′ should be subtracted from the 35′ number each time a 90-degree elbow is used. GOOD! Flame-resistant steel 90-degree metal elbow for dryer ducts.
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.
It works just fine and never gives us any trouble. We just fill it with water and connect the dryer duct. The water in the bucket collects the lint, and we change the water from time to time.
Close vent offsets between dryer and wall vent located on same wall as dryer (Offsets between 6-9 inches): The MV-90 can be coupled directly to a standard 4 inch diameter, adjustable, 90 degree elbow which creates a 9 inch offset.
When installing a dryer vent for laundry centers in basement locations, the vent hood on your home's exterior must be at least 12 inches from the ground. A dryer duct should be 25 feet or less. Subtract 5 feet for each 90-degree turn and 2 1/2 feet for each 45-degree turn.
Duct vents at exterior should be a minimum of 3 feet from any other opening; window, door, other vents, etc. Duct vents at exterior should be at least 6 feet from the A/C condensing unit. Duct vents should never be terminated in the attic or crawlspace. Never combine dryer venting with any other venting source.
If the dryer is against an exterior wall that is not underground, run the duct straight out from the back of the dryer. Set the vent a minimum of 12 inches above the outside ground. Note: This is the simplest, most ideal solution. The shorter the distance and fewer the turns the better for dryer vent installation.
Flexible duct collects lint.
The typical maximum-allowable duct run for dryers is 25 ft.; anything longer than that requires a booster fan. The 25-ft. limit presumes a 4-in. -dia.
When a dryer vent becomes disconnected the warm moist air terminates wherever the damage to the vent has occurred. Air from a dryer vent provides a conducive condition for mold and other fungal growth. Because attics and crawlspaces are unfinished areas of a home, they are already more susceptible to mold growth.