What is the dryer vent rule?

Author: Angelita O'Kon  |  Last update: Tuesday, September 30, 2025

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.

What is the code for dryer venting?

Codes and Standards

In the United States, most home inspectors refer to the International Residential Code (IRC) M1502 for dryer venting. However, some states may have additional regulations. The International Mechanical Code (IMC) 504 also includes extensive clothes dryer requirements.

Does a dryer vent have to be vented outside?

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.

What is the proper route for a dryer vent?

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.

How high does a dryer vent need to be off the ground?

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.

Dryer Venting | Potential Issues & Best Practices

Why does a dryer need to be 18 inches off the ground?

Keep flammable materials and vapors, such as gasoline, away from the dryer. Place dryer at least 18 inches above the floor for a garage installation. Failure to do so can result in death, explosion or fire.

What are the rules for dryer venting?

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.

Where not to put a dryer vent?

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.

How far can you run a dryer vent without a booster?

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.

Is 20 feet too long for a dryer vent?

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.

What happens if you can't vent your dryer outside?

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.

Can a dryer vent have a 90 degree angle?

Vent elbows are available which is designed to turn 90° in a limited space without restricting the flow of exhaust air. Restrictions should be noted in the inspector's report. Airflow restrictions are a potential fire hazard.

Can you use a flexible duct for a dryer vent?

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.

What kind of venting does an electric dryer need?

PVC or plastic ducts are common because they're easy to install but they can trap lint. For clothes dryer venting, a 4-inch, rigid aluminum or galvanized steel duct pipe is a better option. They let air flow more freely and reduce lint buildup.

What is the clearance for a dryer vent termination?

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.

How do you know where your dryer vent is?

On the back of your dryer, you will find the unit's ventilation hose. The hose then leads to the exhaust vent, which will typically be located outside your home.

How long can a dryer cord be?

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.

Can you run a dryer vent up through the roof?

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.

What is the code for venting a dryer?

M1502.

The passageway of dryer exhaust duct terminals shall be undiminished in size and shall provide an open area of not less than 12.5 square inches (8065 mm2).

Does an electric dryer vent have to be vented outside?

In conclusion, while traditional electric dryers do require a vent to the outside to expel moist air, advancements in technology have brought ventless options to the market.

Can you zip tie a dryer vent?

The flexible nature and expandable configuration allow most installs to occur without any modification to the duct or the wall penetration. A pair of jumbo zip ties and you're good to go…at least for a few months until all of the internal bumps and ridges begin to clog with lint.

Can gorilla tape be used on a dryer duct?

A: The tape is flammable and burns very well so I would not recommend it.

What happens if dryer vent is not connected to outside?

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 all dryers have a second lint trap?

Some dryer vent installations also have an external lint trap, which is also known as a secondary dryer lint trap or a 4″ In-Line Dryer Lint Trap.

Is it better to vent a dryer vertically or horizontally?

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.

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