Dryer Vents – The Exhaust System for Dryers

dryer vents In our last publication, we talked about dryer ducts.  Dryer ducts are attached to the clothes dryer and run to a dryer vent intended to vent to the exterior of the home.  Dryer ducts and the dryer vents are part of the entire dryer ventilation system.  Often times, these terms will be used interchangeably.

Clothes dryers evaporate the water from wet clothing by blowing hot air past them while they tumble inside a spinning drum. Heat is provided by an electrical heating element or gas burner. Some heavy garment loads can contain more than a gallon of water which, during the drying process, will become airborne water vapor and leave the dryer and the home through an exhaust duct leading to a dryer vent.

Recap on Fire Hazard – Dryer Vents

As we mentioned in our previous article, dryer ventilation systems are potential fire hazards.  Along with water vapor evaporated out of wet clothes, the exhaust stream carries lint – highly flammable particles of clothing made of cotton and polyester. Lint can accumulate in an exhaust duct or vent reducing the dryer’s ability to expel heated water vapor, which then accumulates as heat energy within the machine. As the dryer overheats, mechanical failures can trigger sparks, which can cause lint trapped in the dryer vent to burst into flames. This condition can cause the whole house to burst into flames. Fires generally originate within the dryer but spread by escaping through the ventilation duct, incinerating trapped lint, and following its path into the building wall.

Venting Requirements – Dryer Vents

A vent that exhausts moist air to the home’s exterior has a number of requirements:

Check Connections

It should be connected. The connection starts with the ducting and is usually behind the dryer but may be beneath it. It then leads into the wall to the vent at the exterior of the home.  Look carefully to make sure all parts are actually connected.

Keep it Straight

Ducting and venting should be as straight as possible and cannot be longer than 25 feet. Any 90-degree turns in the vent reduce this 25-foot number by 5 feet, since these turns restrict airflow.

Vent to the Exterior

Exhaust ducts shall terminate on the outside of the building or shall be in accordance with the dryer manufacturer’s installation instructions. In general, an inspector will not know specific manufacturer’s recommendations and will not be able to confirm the dryer vent’s compliance to them, but will be able to point out issues that may need to be corrected.

Vent Away from Doors & Windows

Exhaust ducts shall terminate not less than 3 feet in any direction from openings into buildings.

Keep it Going One Way

Exhaust duct terminations shall be equipped with a backdraft damper. A backdraft damper is an isolation damper allowing air in one direction only.

Avoid Screens

Screens shall not be installed at the duct termination.

Unsafe Findings for Dryer Vents

dryer vents Ed Lawton, Inspector at B to B Home Inspections, has seen many dryer vents terminate in to crawlspaces or attics.  This is not a safe place to vent.  Remember, we mentioned above, how much water vapor moves through the vent system?  Vents discharging to a crawlspace or attic is depositing moisture to that area, which can encourage the growth of mold, wood decay, or other material problems.

Sometimes, Ed has seen vents terminate just beneath attic ventilators. This, too, is a defective installation.

Remember, dryer ventilation systems must terminate at the exterior and away from a door or window.

Ed has seen screens present at the duct termination.  Screens are often installed by unknowing homeowners seeking to keep critters out.  However, screening provides an optimal place for lint to accumulate.

Interesting Finding

As we mentioned, the dryer vent is not vented properly when venting to the crawlspace.  A completely unsafe condition is this interesting finding: dryer lint being collected into a large produce bag in the crawlspace. Ed recommended that the dryer venting system be properly vented to the exterior with rigid metal vent and flexible metal vent connectors.  He further suggested that the buyer find a qualified contractor for further evaluation and repair.

How to Clean Dryer Vents

As with the dryer ducting, the dryer vent at the exterior can become clogged with lint over time, causing the dryer to dry less efficiently and resulting in dangerous house fires. To clean your dryer vent, remove the outside cover on the vent, and use a special lint brush with an extendable handle to clean the inside of the pipe.

Periodically check while the dryer is operating to make sure that the air exhaust vent pipe is not restricted and the outdoor vent flap will open. Clean lint out of the vent pipe once a year.  Learn how to clean your dryer vent in the video below.  Please note – this is not Ed.

Watch video!

Caps for Dryer Vents

There are a lot of vent caps on the market.  Many of these caps come with screening or caging, both of which are potentially unsafe as mentioned above.  You want a vent that keeps pests out, minimizes drafts and wind clap.  You want optimal air flow to save energy and thus dry your clothes faster.  However, you don’t want a screen to clog the lint.  You don’t want flaps that can break off and clog the vent. 

To prevent unwanted visitors, consider installing a back-draft damper within the duct line.  The damper has a spring-controlled flap that remains shut until the force of the dryer air pushes it open.

It is our hope that, after reading these two articles on dryer ducts and dryer vents, you are checking your own dryer ventilation systems and ensuring they are free of lint.  If you have any questions, please don’t hesitate to call Ed at 609-287-7880 or contact him via email at ELawton@btobinspections.com.  Stay safe!