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Neighbor’s Cigarette Smoke Coming Through The Bathroom Fan

If you are a non-smoker, then you most probably find the smell of cigarettes to be particularly offensive. Your bathroom fan is supposed to improve indoor air quality, not make it worse. And the way the smoke clings to the walls, curtains, and towels—well, you’d probably start to resent your smoker neighbor.

The most likely cause and the best solution to this problem lies in a device called a backdraft damper. The exhaust system in the bathroom uses a backdraft damper to prevent air from traveling the wrong way through the system, i.e., in the direction of the bathroom.

The smell of cigarette smoke through your bathroom fan is most likely related to your damper. If a backdraft damper is not installed, or if the damper is poorly installed, defective, or damaged, it will allow air from outside, or from another apartment, into the vent and out through the fan.

What Is a Damper and What Does It Do?

A damper is a manual or automatic valve, plate, or blade system that functions according to airflow, electrical signal, and/or gravity. The device’s purpose is the control or regulation of airflow and/or prevent air flowing back into a room or through a vent (depending on what type of damper it is).


There are several types of dampers, but for this topic, a backdraft damper is the only one that needs consideration.

A backdraft damper is specifically designed to prevent exhausted air from flowing back into the house as well as to stop air originating from outside or elsewhere in the ventilation system from entering the house.

Or at least, this should be the case with a properly installed and correctly functioning backdraft damper.

How Smoke Gets In Through the Fan

When the fan is running, air is forcefully pulled out of the bathroom and pushed through the ductwork to the outside. This means that you are unlikely to smell cigarette smoke while the fan is operating, even when the backdraft damper is missing or broken.

It is when the fan is off that a broken or missing backdraft damper causes problems.

If your neighbor’s favorite smoking spot is just over the wall from the terminal vent of your bathroom fan, then without a functioning damper, this smokey air can waft in through the vent, along the ducts, and out of your bathroom fan.

Illustration of a man smoking in his bathroom and a man on the next unit covering his nose because of the smoke illustration

Another possibility applies if you are in a place that has a shared ventilation system (common in apartment buildings).

In such cases, if your neighbor smokes in their apartment, the smoke is pulled into the vents by the exhaust systems. When there is no backdraft damper preventing their exhausted air from entering your ducts, then the smoke can waft out through your fan.

Is the Smoke Coming Through the Fan?

If you particularly notice the smell when you turn your bathroom fan on, then the chances are that the smell is not actually coming through the fan.

Instead, you should look for other vents, doors, or windows through which the smoke can be pulled. When the bathroom fan is running, it is pulling air from the bathroom into the ducts but it is also pulling air from other places or outside into the bathroom to replace the exhausted air.

Where Should Backdraft Dampers Be Installed?

If you are trying to counteract the inflow of cigarette smoke from your neighbor, then the position of the backdraft damper can make a difference.

Theoretically, wherever you place it, the damper should function to stop cigarette smoke from coming in through your bathroom fan.

In reality, however, backdraft dampers are not 100% airtight, and a damper just behind the fan would mean that the smoke can concentrate in the ducts and have ample chance to leak through the fan.

You would do better to install it at the terminal vent, which prevents the smoke from ever entering your ducts. Even the marginal air leakage is not going to be an issue because the smoke will rapidly dissipate in the open air before it can leak through the closed backdraft damper.

Bathroom fan causing high exhaustion rate while the air pressure drops inside the bathroom illustration.jpg

In a shared residence, such as an apartment building, the ventilation system typically comprises a main central duct to which the individual ducts from each apartment connects.

Backdraft dampers should be installed where the individual ducts connect with the main duct to stop the neighbor’s cigarette smoke from coming in through the bathroom fan.

Now let’s look at what can go wrong with these backdraft dampers, which would allow the cigarette smoke to come through.

Potential Problems With A Backdraft Damper

Wrong Type of Damper Used

There are four main types of dampers

  1. Backdraft dampers
  2. Balancing dampers
  3. Control dampers
  4. Safety dampers

You need to use a backdraft damper to stop the smoke from coming through as this is the only damper where prevention of backflow of air is the primary design purpose.


Balancing dampers balance air pressure in rooms and the ventilation system. This damper should allow air to flow either into or out of the room to maintain this balance.

Control dampers use manual, electrical, or pneumatic motors that actively regulate airflow. These are used within the ducts and vents of a ventilation system.

Safety dampers are safety devices that shut off in the event of a fire and the accompanying smoke.

As you can see, the backdraft damper is the only appropriate damper that would fulfill the need for venting air exclusively unidirectionally according to the activation of a bathroom exhaust fan.


If the wrong damper is being used, the only solution is to remove the installed damper and replace it with an appropriate backdraft damper.

I always recommend the AC infinity dampers. They are extremely airtight and quiet. Not only will they keep the cigarette smoke out, but they also will prevent bathroom fans from dripping and can stop any wind noise that comes from the vent.

AC Infinity 6" Backdraft Damper, One-Way Airflow Ducting Insert with Spring-Loaded Folding Blades for 6” Ducting in Range Hoods and Bathrooms Fans
  • An antidraft duct insert designed for use with range hoods, bathroom fans and other home HVAC applications.
  • Features outer rubber gaskets that create an airtight seal and grip between the damper and ducts.
  • Mounts horizontally or vertically to prevent backflow and debris from entering ducting.
  • Galvanized steel body with spring-loaded aluminum damper blades that open with minimal airflow.

Last update on 2024-03-27 / Affiliate links / Images from Amazon Product Advertising API

Incorrect Installation

When installing the damper, the manufacturer’s instructions must be followed. This will ensure that the damper is able to work optimally and with the longest lifespan possible.

If the damper is installed backward, you can check this yourself. Check whether the valve is opening toward the outside and not towards the fan.

The damper may be too big or too small for your ducting system. This will be noticeable by the ill-fitting connection between the damper and duct and any quick fixes someone may have done to force the connectors to “fit”.

As it is against the code, and therefore illegal, to install a damper against manufacturer instruction, the installer should be willing to come and fix it for you at no cost.

It’s worth noting, according to the International Mechanical Code (IMC) Section 803.6, the name of the installer is supposed to be put on a label on the damper.

Depending on how much information is provided (if they’ve just written “Dave”, it won’t help you), this might make it possible to contact the people who installed the damper incorrectly.


In any of these situations, you will need to check that your ducting has not been damaged. If it has, you are going to need to repair or replace it.

Man checking flexible duct pipe installed in the ceiling

If the damper is facing the wrong way and has managed not to damage the ducting and is intact itself, you may simply need to remove it and reinstall it correctly.

But aside from that, the solution is to buy a new and appropriately sized damper and install it according to the directions from the manufacturer.

Damaged Blades

The blade system of a damper involves a one or a set of blades that, using a motor, spring, or hinge/gravity mechanism, will open or close.

The blades are designed to lie flat against each other and create a seal for the air backflow. If the blades do not close completely, this seal is not formed, and air cannot be blocked.

These blades can be warped, in which case they won’t open or close properly, and cigarette smoke can get past to the duct behind.

The blades can also be cracked or chipped. The infiltration of smoke in such cases will be slower because a crack or chip is a smaller opening compared to a poorly closing blade.

There can also be an issue with the closing mechanism (hinges, springs, or electrical components), meaning that the blades, while unwarped, uncracked, and unchipped, will simply not close, and the smoke can just blow through the ducts and escape through your bathroom fan.


If your blades are not closing correctly, you should check that the mechanism is clean. There may be dust and dirt blocking the blades from moving correctly.

If you have an electric damper, the next step would be to check the components of the electrics.

If the blades or electric unit are damaged, you will need to replace the damper.

Compromised Seal

Some backdraft dampers have a rubber seal which wraps around the housing to seal it into the duct.

If the seal is compromised, the blades may still close properly, but the whole damper unit is no longer airtight and smoke can enter the ducts and reach your bathroom.

Backdraft damper with rubber seal illustration

The seal can become damaged due to age, which is not helped by the constant exposure to hot and humid air.

The seal can also be defective from the start. On the other hand, it may just be dirty, preventing it from sealing properly.


You need to clean the seal if there is dirt causing the seal to be compromised.

Otherwise, you should be replacing your seal. Just double-check that replacing the seal alone is worth it. In some cases, it may be more economical to replace the whole damper, particularly if you are thinking of upgrading to a better model.

Defective, Broken, or Old Electrical Components

Some backdraft dampers are operated by motors, which means that there are electrical components to the system. An electrical signal causes the blades to open and the removal of this current closes them again.

These electrical components can be defective, break, and suffer from wear and tear with age.

When the electrical component fails in such a way that the blades do not close properly, they don’t ‘close at all, they open again after closing, etc., then any cigarette smoke that is trying to get into the ducts can get in.

This is only applicable for an electrical damper with a motor and will not apply to a gravity-operated or spring-loaded damper.


You can look into replacing the electrical component or making small repairs (maybe it’s just a minor wiring issue). However, as with the seals, you should check if replacing the electrical unit is worthwhile considering the affordability of a new damper.

If you decide on repairs or electrical replacements, you may wish to call an electrician in to ensure that the electrics are safe and properly maintained.

How to Install a New Damper

Since so many of the problems can be solved by replacing the damper, knowing how to install one can be very helpful.

When installing the backdraft damper, ensure that you are following the manufacturer’s instructions. Because these will differ depending on the make and model, the following instructions will be generalized.

  1. Remove the old damper.
  2. Choose a new one (it must be listed and labeled and sized correctly).
  3. Decide on the best location.
  4. Clean the duct where you will be installing the damper so that there is no dirt preventing the seal from sealing properly.
  5. Slide the damper into the duct (keep it straight and ensure that the blades open in the correct direction).
  6. The seal should make the damper fit tightly. You can further secure it with a few beads of silicone.

The following video provides a practical and step-by-step guide to installing a backdraft damper:

Yellow Streaks Could Be Caused By Cigarette Smoke

If your neighbor’s cigarette smoke has been contaminating your bathroom for years, for example, if they are trying to hide their habit from a roommate, significant other, or landlord, there could be some residue left on the walls. This residue will turn yellow once water condensates on the walls.

Ultimate Backdraft Damper Guide | All You Need to Know


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