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What Is Backdrafting? And How to Prevent it?

This article covers what a backdraft is, why it can be dangerous, and how to prevent it so you can keep your kitchen properly ventilated.

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If you own a ducted range hood, you want to ensure that it operates as efficiently as possible. This involves reducing or eliminating back-drafting from your range hood’s exhaust duct system. But what is backdrafting, and how do you prevent it?

This article covers what a backdraft is, why it can be dangerous, and how to prevent it so you can keep your kitchen properly ventilated. We’ll also talk about what can happen if the problem isn’t addressed.

Backdrafting happens when outside air enters your range hood duct and becomes trapped inside the duct. This air is then forced back into the kitchen, hence the term “back drafting.”

What is backdrafting?

A backdraft is a reverse movement of air. Backdrafting occurs when air that is meant to be ventilated outside, gets trapped in the ductwork of the home. That air can then make its way back into the home or remain in your ducts, allowing grease and oil to stick to the sides of your ductwork. This severely reduces the efficiency of your ventilation system.

How to limit or prevent backdrafting

Here are five tips for preventing backdrafting in your range hood duct.

1. Use a backdraft damper

You can install a backdraft damper in line with your ductwork or at the point where your hood meets the ductwork.

A backdraft damper prevents outside air from entering the range hood duct. This is the most effective method of preventing back-drafting in the first place. As soon as the hood is turned on, the damper opens, allowing fresh air to enter your home from the outside. When you turn off your hood, the vent closes, preventing outside air from entering the duct.

Installing an inline backdraft damper a few feet away from the outside of your home will yield the best results.

2. Use a wall or a roof cap

Installing a wall or roof cap at the end of your duct run will help to further reduce the possibility of back-drafting. As a result, not only does outside air not get into the duct, but it also prevents leaves, dirt, and small animals from getting into your ductwork.

3. Limit the length of your duct run

In order for the range hood to be effective, it must move the air with enough force to get it out of the duct and out of the home. As a result, if your duct run is excessively long, the air in your duct may become stagnant and begin to flow back into your kitchen.

4. Reducing the number of elbows in your ductwork

The more elbows you use, the more work is required to exhaust the air in your kitchen, this can significantly increase the chance that unwanted air will get trapped inside your ductwork. If you absolutely must use more than two elbows, we recommend getting a range hood with enough CFM to handle the twists and turns in your ductwork. 

  • Consider including at least 18 inches of a straight run before adding an elbow when installing your ductwork. 
  • For each elbow in your ductwork, five feet should be added to the total length of your duct run.
  • Ensure there are at least 24 inches of straight duct between each elbow before installing the duct.

5. Keep your filters clean

Using clean range hood filters will guarantee that the air coming from your kitchen is circulated smoothly through your range hood.

Inside a clean ventilation ductwork.
Inside a clean ventilation ductwork.

What are the consequences of backdrafting?

If you don’t take care of the backdraft in your home. There can be significant drawbacks (no pun intended.

1. Grease will accumulate in your ductwork

When backdrafting occurs, not all of the kitchen air will make it to the outside. Some of that air will remain trapped within the ductwork. Over time, the grease and oils from that air will stick to the sides of the duct, lowering the efficiency of your range hood’s performance significantly.

In most cases, you will never have to clean the ductwork in your range hood. Just make sure to clean those filters every three to six weeks to keep them running smoothly.

2. Your range hood’s lifespan will decrease

Backdrafting occurs when outside air pushes against inside air that’s trying to escape through the kitchen vents and into the outdoors. And the duct system must contend with a great deal of resistance.

As a result, your hood’s motors need to work harder to move the air out of your home. Over time, this puts a significant amount of strain on the motor, reducing the lifespan of your range hood.

3. Smoke and odors will remain in your kitchen

As time passes, you may begin to notice that smoke and cooking odors aren’t leaving your kitchen as quickly as they once did. 

If you notice that your hood isn’t working properly, check to see if you have a backdraft damper and a wall or roof cap installed. 

Double-check your duct installation to ensure that you follow the industry’s recommended procedures. 

If you want to see how these dampers work and how to install one, take a look at this video called Back Draft Damper Installation – How to install a damper from the Fresh Air Manufacturing Co. YouTube Channel.

Video called Back Draft Damper Installation – How to install a damper from the Fresh Air Manufacturing Co. YouTube Channel.

Frequently asked questions (FAQ)

Do you still have questions? Below are some of the most commonly asked questions about vent hoods and backdrafting.

What is home backdrafting?

A “backdraft” occurs in your home when an appliance or device that uses combustion (an open flame) is not properly vented, allowing the exhaust to be drawn back into the home.

What causes a backdraft to form?

A backdraft occurs when air is suddenly introduced into a fire, depleting most of the available oxygen in a room or building. Because a fire requires air, fuel, and heat, the latter two must also be present. 

How do you test for Backdrafting?

I simply cup my hands around the draft hood without touching it to check for a proper draft. I’ll notice warm, damp air flowing out of the draft hood if the water heater is backdrafting.


this article discusses what back drafting is, how it works and how to prevent it. We hope you use this information to take any backdrafting issues you may have or prevent them from ever becoming an issue in the first place. Below are some key takeaways:

Key takeaways

  • Backdrafting should be avoided.
  • A ductless range hood will not cool down your kitchen. Only a ducted hood will.
  • The air outside should be cooler than inside to cool down the kitchen.
  • Don’t leave your hood fan on for more than 2 hours at a time.

So, is your kitchen well protected against backdrafting? And did we cover everything you wanted to know? Let me know in the comments section below (I read and reply to every comment). If you found this article helpful, check out my full blog for more tips and tricks for your kitchen. Thanks for reading, and stay safe.

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Written By Roger Harris

Hey there, My name is Bradley, and I've been riding fixed for over ten years. I love all the joy and pain that comes with this unique style of cycling and the passionate community that drives it. If you love fixed gear and single-speed bikes, this is the place for you.

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