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. 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.
Be sure to keep 90-degree bends to a minimum. Every 90-degree bend is the equivalent of ten feet of vent run. Never install a dryer vent which has a bend greater than 90 degrees. Sharp bends restrict airflow and will lead to excessive lint buildup.
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.
Termination. The exhaust duct should terminate outside the building at least 3 feet from any building opening, and at least 10 feet from an air conditioner or heat pump condenser (reference).
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 effective length of a dryer duct with bends increases by 2.5 feet for each 45 turn and 5 feet for each 90-degree curving. If a clothes dryer vent is 25 feet long and has three 90 elbows, which is very common, it would have an equivalent measure of 25 + (3×5) = 40 feet!
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.
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.
Dryer Vent Locations
The best place is usually an exterior wall, which allows the duct type to be as straight and short as possible, minimizing lint buildup and reducing the fire hazard.
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.
In most states, indoor dryer vents are not legal. Colorado's residential code, for example, initially states that dryers must be vented according to manufacturer instructions, which could allow for indoor or outdoor venting. The next section, however, says that dryer exhaust vents shall convey moisture outdoors.
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.
What does the D90 error code mean? If the display panel on your LG dryer is displaying the D90 error code, it means the airflow through your dryer's ventilation system is obstructed, and hot air cannot exit your dryer through the vent. The code is caused by a build-up of lint or other debris in the ventilation system.
Termination of dryer venting must be to the exterior with a proper hood or roof cap equipped with a backdraft damper. Small orifice metal screening should not be part of the hood or roof cap as this will catch lint and block the opening in a very short time.
The tables include two 90-degree elbows. The table values should not be derated for venting systems with one or two elbows. For each additional elbow over two, (see Figure 510.1. 2) derate the table values by 5 or 10 percent, depending on the angle of the elbow.
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.
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.
The minimum duct air velocity during normal operating 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.)
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.
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.
If you have a gas-fired dryer, it's not only a bad idea to vent it into your garage, it's potentially deadly.
PVC is plastic and not conducive for dryer vents. When lint travels through a PVC pipe, static electricity created by the plastic will pull the lint to the sides. Over times this causes a 4” pipe opening to shrink dramatically. This leads to poor airflow which creates drying exhaust issues.
Fire Hazards: Running a traditional dryer without a vent leads to dangerous lint buildup, increasing the risk of fires. Moisture Damage: Without proper ventilation, trapped humidity can encourage mold and mildew growth, affecting indoor air quality and structural integrity.