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How to Stop Wasps Coming Through Vents

Wasps in the house are unwelcome to most people and deadly to some. There are multiple ways that they can get into the house but few people consider air vents as a point of entry until they see the wasps coming in that way.

Happily, there is a very simple solution to this problem and it’s one that will solve a whole lot of other problems as well!

Installing a backdraft damper will stop wasps and other insects from entering the duct and your home. The damper can be installed either inside the duct or at the termination point on the roof/wall.

Installing a Backdraft Damper Will Stop Wasps

Wasps and other bugs can be stopped from entering the ducts and escaping into your house through the exhaust fan grilles by purchasing and installing a relatively inexpensive duct accessory.

What Is a Backdraft Damper?

Backdraft dampers are devices installed in exhaust ventilation ducts that only open in one direction, ensuring one-way flow of air, and only when acted upon by a force (electric backdraft dampers are an exception as they are opened by electrical current).

A backdraft damper is typically short, hollow cylinder with one or two hinged flaps covering the diameter of the cylinder, either in the center or over one end.

AC Infinity 4" Backdraft Damper, One-Way Airflow Ducting Insert with Spring-Loaded Folding Blades for 4” Ducting in Range Hoods and Bathrooms Fans

The hinged flaps open out in the same direction as the air being pushed through the duct by the fan, i.e., they open outwards. They cannot swing in the other direction.

This means that air from the room being vented can leave the ducts but cannot re-enter them passively or when directed back against the terminal vent by the wind.

In addition, cold or hot drafts from the outside cannot be blown into the house through the exhaust system.

How Backdraft Dampers Work

Since we’ve already touched on electrically-operated dampers, let’s start with how these work.

A switch controls the flap or flaps. The vast majority of the time, this switch is linked to the on-switch of the fan. So, when the fan is turned on, the flaps open. When the fan is turned off, the flappers close again.

Some dampers are operated by gravity (pictured below). These often only have one flap with a hinge in above the horizontal midline. The force of the exhausted air pushes the flap open on its hinge. Then, when this force is removed (the fan is switched off), the flap swings closed because of gravity.

HVAC OV 6" inch Duct Connector with air Backdraft Damper. Made of Durable Plastic. Ducting with Non Return Valve.

Now we come to my preferred opening mechanism: spring-operated hinges. If you jump back to the image in the first section, you can clearly see one of these dampers.

Unlike gravity dampers, these ones almost all have two flaps with the hinge along the horizontal or vertical midline.

The coil of the spring keeps the flaps shut until they are opened by a strong enough force, i.e., the air being pushed against them by the exhaust fan. Once the force ceases, the springs snap the flaps closed again.

Here is an helpful guide if you would like to learn more about ventilation dampers.

Quality Materials and Design Are Important

Not just any backdraft damper will do.

As I mentioned, the spring-operated ones are my top choice. They are more reliable and less vulnerable to malfunction than gravity dampers and electric dampers.

Gravity dampers can be picked up by breezes and the like moving in just the right direction. Not only does this give the drafts an opportunity to get into the ducts but when the flap gets dropped, it can make a terrible banging sound.

HVAC OV 6" inch Duct Connector with air Backdraft Damper. Made of Durable Plastic. Ducting with Non Return Valve.

Electrically-operated dampers just have more components that can cause them to malfunction. If something goes wrong with the wiring, then the damper flaps will stay shut when the fan is on, causing exhaust to backup in the ducts and house.

They can also get stuck open, which would make the damper completely pointless.

The dampers should have a proper rubber seal to make it fit snuggly and securely in the duct. A tight seal will prevent air from passing the wrong way in the ducts. It will also stop any insects from getting past.

The gap would have to be relatively large for a wasp, but with a poorly designed backdraft damper or one that is ill-fitted to the duct in which it is installed can create a large enough space.

Which Backdraft Damper is Best?

Everywhere on this site, I recommend AC infinity dampers (amazon link). Not only do their products look great, but they are also designed using quality components with the strictest quality control procedures in the industry. (For residential dampers)

AC Infinity 4" Backdraft Damper, One-Way Airflow Ducting Insert with Spring-Loaded Folding Blades for 4” Ducting in Range Hoods and Bathrooms Fans
AC Infinity backdraft damper

The flaps on the backdraft damper must fit perfectly inside the housing. This is where the AC infinity dampers shine. The flaps move easily, yet close completely when the exhaust fan is turned off.

There Is a “Best” Location for the Damper

The best location for the damper is close to the external termination point.

If you install the damper too far inside the vent, you will leave room for the wasps to nest within the vent, attracted to the warmth and moisture.

The optimal distance from the terminal vent is about 10 inches.

Wall/Roof Cap With Integrated Backdraft Damper

Backdraft dampers are not always separate devices. You can also get wall or roof caps with integrated dampers, i.e., dampers that are built in as part of the unit.

Builder's Best 084633 Galvanized Steel Roof Vent Cap with Removable Screen & Damper, 6" Diameter Collar, Black

These are typically gravity-operated dampers, so you do have to contend with the issues associated with these. And they are particularly prone to flapping when installed at the terminal vent as this is where it is most vulnerable to the effects of wind.

What if You Already Have a Damper?

If you definitely already have a damper, but wasps are still coming in through the fan, then there are two potential issues.

  1. The damper is not air-tight. You can try to use silicone seal on your existing damper or you can buy a new one.
  1. Dampers can break or become obstructed so that the flaps don’t close properly. Clearing obstructions is usually as easy as accessing the damper. However, if the backdraft damper is broken, you will need to replace it. There is very little point in trying to repair it.

Additional Benefits

In addition to keeping pests out of the ducts here are a couple of more reasons to install a backdraft damper

  • No more cold drafts from the vents
  • Energy savings
  • Better air quality
  • Condensation won’t drip from the vent

Avoid Vent Wall Caps With a Net

Nets installed over or integrated into vent caps will keep insects out, but they can also drastically reduce the airflow and energy efficiency of the exhaust ventilation system.

Vent Systems 4'' Inch - Graphite - Soffit Vent Cover - Round Air Vent Louver - Grill Cover - Built-in Insect Screen - HVAC Vents for Bathroom, Home Office, Kitchen

Screens catch dust and debris, which build up and shrink the open ventilation area. The air takes longer to exit the duct, which encourages condensation with in the ducts. When condensation drips back into the house it can cause all sorts of issues.

In addition, the fan motor will be straining to perform its function and will have to be left on for longer in order to achieve proper ventilation. This increases the rate of wear and tear on the motor.

Humane Way to Get Rid of Wasps and Other Insects in Vents

If the wasps have invaded your ducts and built their nests, then you will need to get rid of them before attempting a permanent solution to wasps coming in through the fan.

People usually get rid of wasps by killing them using pesticides, swatting or pulling down their nests, and so on.

These methods, while easy, are inhumane and are unfriendly to the environment. We’re all about the environment here! 

Wasps are beneficial to the ecosystem. They help with pollination and are a natural way of controlling pests in your garden.

If you are growing succulents, for example, you will want to keep wasps around to deal with white mites and other pests. Ordinary pesticides usually kill succulents and this might be the motivation you need to keep wasps around.

Here is how you can get rid of wasps inside ventilation ducts without hurting them:

  • Turn on the exhaust fan at full speed
  • Every couple of hours spray a little bit of spearmint-infused water into the duct (use a few drops of essential oil in the spray bottle)
  • Keep the fan running until the wasps move out (usually, they will leave within 24 hours since they don’t like spearmint and the constant high airflow)
Rayson Empty Spray Bottle, Frosted Assorted Colors

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