What Is Backdrafting? And How to Prevent it?

What is Backdrafting? In this article, we will answer that question and provide some its to help you prevent backdrafting in the first place.

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If you own or recently installed 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?

This article will cover what backdrafting is, why it’s important, and how to prevent it so you can keep your kitchen properly ventilated. We’ll also discuss 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 forced into the kitchen, hence the term “back drafting.”

What is backdrafting?

A backdraft is a reverse movement of air. Backdrafting occurs when air meant to be ventilated outside gets trapped in the home’s ductwork. 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. Backdrafting is not done intentionally, and some malfunction often causes it.

Image of the inside of a ventilation ducting system with fan.
Image of the inside of a ventilation ducting system with fan.
My favorite range hood (at the moment):

COSMO COS-63190S Wall Mount Range Hood

What is backdrafting? And how to prevent it? | 71ddmbmvgwl. Ac sl1500 | range hood homeland
My favorite range hood (at the moment):

COSMO COS-63190S Wall Mount Range Hood

This is one of the best hoods available at this price point. Reasonably strong CFM for the cost, and it has received rave reviews (over 3,800 reviews!). It looks great, and the LED lights provide a pleasant brightness. For the price, its performance and style are outstanding. Highly recommended!

What are the consequences of back-drafting

back-drafting can have many consequences on your kitchen and home. Not to mention your safety. Below are just some consequences of failing to address back-drafting.

1. Grease will accumulate in your ductwork

When backdrafting occurs, not all of the kitchen air will make it to the outside. Instead, 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. Instead, make 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, 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 hoods 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 notice that smoke and cooking odors aren’t leaving your kitchen as quickly as they once did. 

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

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

Five tips to help you 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. The damper opens as soon as the hood is turned on, 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 reduce the possibility of backdrafting further. 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

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 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 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″ of the straight run before adding an elbow when installing your ductwork. 
  • Five ′ should be added to the total length of your duct run for each elbow in your ductwork. Consider the following example: a 25-yard straight run is about the same as a 15-yard run with two elbows.
  • Ensure there is at least 24″ of straight duct between each elbow before installing the duct

5. Keep your filters clean

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

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

A video called Back Draft Damper Installation – How to install a damper from Fresh Air Manufacturing Co.

Frequently asked questions (FAQ)

Do you still have questions? Below are some of the most commonly asked questions about back-drafting.

What are the risks of a backdraft?

There are several risks associated with back-drafting, the most significant of which is the risk of carbon monoxide poisoning. Backdrafting can also pose a fire hazard if the combustion gases from your stove or oven escape and ignite something in your home.

A backdraft can produce an explosion, putting firefighters and others in danger.

How do you perform Backdrafting testing?

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

Backdrafting is caused by what?

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


Now that you know what backdrafting is don’t let it happen to you. Backdrafting is a dangerous practice that can cause serious harm to your health and the environment.

This article covered what backdrafting is, why it’s important, and how to prevent it so you can keep your kitchen properly ventilated. We’ll also discuss what can happen if the problem isn’t addressed. Here are some key takeaways:

Key takeaways

  • A range hood can keep your kitchen cookery clean.
  • 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.
  • The hot gases are released into the room when the furnace passes air through a heater. If there are combustibles in the area, then those can be ignited and cause a flue fire or flames to appear inside rooms.
  • Backdrafting is the process of exhaust fan backflow into your house through a broken exhaust duct.
  • It is also called reverse flow, negative pressure, or smoke infiltration.
  • The most significant health risk caused by backdrafting comes from carbon monoxide and other toxic gases.
  • Backdrafting is a venting system malfunction that occurs when the venting ductwork becomes so clogged or damaged due to poor design and maintenance practices that combustion gases can cause backflow into the house.

So, are you having backdrafting issues? And did I cover everything you wanted to know? And what do you think of my list? 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 on range hoods. Thanks for reading, and be safe.

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Written by Roger Harris, Staff Writer

Hey there! My name is Roger, and I've been selling range hoods for over six years. I now run this blog all about range hoods and kitchen ventilation! If you're looking for a new range hood for your kitchen, this is the place for you.

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Edited by Nick Eggert, Staff Editor

Nick is our staff editor and co-founder. He has a passion for writing, editing, and website development. His expertise lies in shaping content with precision and managing digital spaces with a keen eye for detail.

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