Should a dryer vent have a flap?

Whether or not a dryer vent should have a flap is an important consideration for homeowners. The flap on a dryer vent serves an important purpose, but also comes with some drawbacks. In this article, we’ll look at the pros and cons of having a flap on a dryer vent so you can decide if it’s right for your home.

What is the purpose of a dryer vent flap?

A flap (also called a damper or backdraft damper) is installed at the outlet of a dryer vent, on the outside of your home. This hinged flap is designed to open when the dryer is running, allowing hot, moist air to exit the vent. When the dryer shuts off, the flap closes to prevent outside air, moisture, insects, and rodents from entering the vent and ductwork.

The main purposes of a dryer vent flap are:

  • Prevents backdrafts – Stops air from flowing back into the vent system when the dryer is off
  • Keeps pests out – Blocks insects, birds, rodents from nesting in the ductwork
  • Reduces energy loss – Stops warm household air from escaping in winter, hot outdoor air from entering in summer

By serving these functions, a dryer vent flap helps maximize dryer efficiency and prevent damage or clogs in the vent ductwork.

What are the benefits of having a flap?

There are several benefits that a flap on a dryer vent can provide:

  • Prevents lint buildup – Keeps lint contained in the vent rather than allowing it to build up on the exterior wall or roof
  • Reduces moisture damage – Prevents outdoor moisture from dripping down the ductwork and causing mold, mildew, or rotting
  • Minimizes energy loss – Reduces conditioned indoor air escaping outside when dryer is off
  • Lowers energy bills – More efficient dryer operation means lower electricity usage
  • Excludes pests – Rodents, birds, insects can’t enter and nest in ductwork
  • Increases safety – Eliminates drafts which could blow out pilot lights

By keeping air flow moving in the right direction and preventing unwanted entry into the ducts, a dryer vent flap can optimize dryer function and prevent damage.

What are the downsides to having a flap?

However, there are some potential downsides associated with dryer vent flaps:

  • Possible reduction in airflow – The flap creates airflow resistance which can slow venting
  • Flap may get stuck closed – Lint/debris buildup can prevent flap from opening fully
  • Noise from flap movement – Some flaps can create flapping sounds when dryer turns on/off
  • Maintenance required – Flap must be cleaned periodically to ensure proper function
  • Can interrupt automatic dry cycles – Some dryers sense backdrafts and shut off, requiring reset

These potential drawbacks mean the flap needs proper installation and occasional maintenance. A clogged or malfunctioning flap defeats its intended purpose.

How does a dryer vent flap work?

A dryer vent flap consists of a lightweight cover made from materials like vinyl, metal, or nylon attached to a hinge or pivot mechanism. When air pushes through the vent, the flap opens allowing the air to exit. Once the airflow stops, gravity and a spring closure cause the flap to swing closed.

Dryer vent flaps either have a gravity-based closure or a spring-loaded closure:

  • Gravity-based – Relies on weight of flap to keep it closed when dryer is off
  • Spring-loaded – Uses a small spring mechanism to pull flap closed tightly when there is no airflow

Spring-loaded flaps provide a tighter seal which better prevents backdrafts, moisture ingress, and pest entry into the vent ductwork. However, a gravity flap can still function adequately if installed properly.

Where should the flap be installed?

A dryer vent flap should be installed on the exterior termination point of the duct. This allows it to open and close with airflow but prevents outdoor conditions from entering the ductwork.

The proper locations to install a dryer vent flap are:

  • On an exterior vent hood attached directly to the duct
  • On the wall termination if duct exits house directly
  • At the outlet point on an elbow/gooseneck duct

The flap should swing freely open and closed without any obstructions. Installing it too far down the duct run can allow backdrafts in the pipe before the flap.

What are the code requirements?

Most building codes and manufacturers require a flap to be installed on dryer duct terminations. However, specific requirements can vary by local jurisdiction.

Some general code requirements for dryer vent flaps include:

  • Must swing freely and fully open when dryer is operating
  • Made of durable, non-combustible material
  • Should have magnets to hold flap closed when dryer is off
  • Required on both interior and exterior terminations
  • Not allowed on condensing duct installations

The flap must not inhibit the proper exhaust of the dryer. Consult local building codes for applicable requirements in your area.

Should a dryer vent have a flap?

In most cases, a flap is recommended for dryer vents terminating to the outdoors. The benefits, such as preventing backdrafts, moisture ingress, and pest infestation, usually outweigh the minor drawbacks.

A dryer vent flap should be installed if:

  • Vent terminates on roof or wall exposed to outdoor air
  • Vent duct has vertical run that could collect moisture and lint
  • Energy efficiency and proper dryer performance are priorities

However, a flap may not be necessary if:

  • Vent runs short, straight length to outdoors
  • Exterior termination is not exposed to weather elements
  • Flap would create excessive noise or vibration

In exempted situations, the benefits may not outweigh the potential problems. Overall, following manufacturer specifications and local building code requirements is advised.

What are the alternatives to a flap?

For situations where a flap is not practical or desired, some alternative options include:

  • Vent hood or louvered vent cap – Provides protection from elements without flap
  • Angled hood termination – Deflects moisture and deters pest entry
  • Screen – Prevents animals and debris but allows airflow
  • Duct appliance interlock – Uses sensor to shut dryer off when vent blocked
  • Shorter vent run – Eliminates need for flap if duct is very short

Some builders also opt to simply leave the flap off the vent if other protective measures are in place. This avoids potential airflow limitations from the flap.

What maintenance is required?

Like any component, dryer vent flaps require periodic inspection and maintenance. Over time, lint can build up on the flap preventing it from opening fully. Pests can also nest on or around the flap.

To ensure proper functioning, the flap and vent hood should be:

  • Inspected annually
  • Gently brushed and vacuumed to remove lint
  • Checked for any obstructions, damage, or pests
  • Confirmed to still swing freely and seal tightly
  • Replaced if worn out or not functioning properly

A spray-on grease remover can help dissolve any lint buildup. Any screen on the hood should also be cleaned. Catching flap problems early prevents bigger duct obstructions.

Key facts about dryer vent flaps

Some key facts to remember about dryer vent flaps include:

  • Made from sheet metal, plastic, nylon, vinyl
  • Attached via hinge or pivot mechanism
  • Open when dryer is on, close when it shuts off
  • Prevent backdrafts, moisture ingress, pest entry
  • Required by most building codes and manufacturers
  • Should be cleaned 1-2 times per year
  • Require proper installation and maintenance

Understanding how dryer vent flaps operate and their maintenance needs allows homeowners to maximize their benefits. Proper installation is also key to achieve intended performance.

Conclusion

Dryer vent flaps serve an important function, but also require proper installation and periodic maintenance. For most homes, the benefits of including a flap, such as increased energy efficiency, prevention of moisture damage, and exclusion of pests, outweigh the minor drawbacks.

Following manufacturer specifications and local building code requirements for your dryer vent system is highly recommended. With the flap installed in the right location and well maintained, it can help optimize dryer performance and prevent problems.

Consider your specific needs, but in most cases, installing a dryer vent flap can provide homeowners with an extra level of protection. Just be sure to clean it regularly to prevent any lint buildup issues down the road.

Pros of a Dryer Vent Flap Cons of a Dryer Vent Flap
Prevents lint buildup Potential reduction in airflow
Reduces moisture damage Flap may get stuck closed
Minimizes energy loss Noise from flap movement
Lowers energy bills Maintenance required
Excludes pests Can interrupt dry cycles
Increases safety