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Neighbor’s Cigarette Smoke Coming Through The Bathroom Fan

There are few things worse than grabbing for your towel after a shower only to find it smells like you have been sneaking cigarettes in the bathroom. And the smell of cigarette smoke lingers in a way that makes your heart drop every time you need to turn on the bathroom fan when you suffer from this particular ventilation malfunction.

A backdraft damper is likely both the cause and the solution to this problem. The exhaust system in the bathroom uses a backdraft damper to keep the exhausted air out of the bathroom. The reason the smoke is getting in is likely down to a faulty or damaged damper, but a backdraft damper is also the solution to this problem.

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 and/or gravity. The purpose of a damper is the control or regulation of airflow and sometimes the prevention of 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 contaminated air from flowing back into the house. It is installed in ducts that vent areas like bathrooms, kitchens, and attics. Also called butterfly dampers or gravity dampers, they are the key components to preventing the backflow of air into a bathroom.

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

Where Should Backdraft Dampers Be Installed?

Backdraft dampers should be used in the ducts and vents installed for kitchen and bathroom ventilation systems.

Backdraft dampers are essential in bathroom exhaust systems in order to comply with the International Residential Code (IRC), which states in Section M1505.2 that:

“Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or circulated to another dwelling unit and shall be exhausted directly to the outdoors.”

By placing the damper at the outside end of the ducts in the ventilation system, it is able to prevent the exhausted air from re-entering the ventilation system.

This is crucial to preventing odors and potentially dangerous sewer gas from leaking back into the bathroom through the bathroom and plumbing vents. Furthermore, it makes sure that the moisture removed from the bathroom does not find its way back into the ductwork to cause problems there, such as a dripping fan.

In a free-standing house, an exhaust vent must vent directly out of the house. The backdraft damper should be located at this opening for the exhaust vent.

If something is wrong with your damper, then your neighbor’s cigarette smoke can enter the ductwork and make its way out of your bathroom fan. This is particularly problematic if your neighbor’s exhaust fan terminal or favorite smoking spot is located near your vent.

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 as well as where the main duct terminates to the outside.

If there is something wrong with the individual dampers, then smoke from your neighbor’s ventilation system can get into your ducts and leak out of your bathroom fan.

Potential Problems With A Backdraft Damper

Wrong Type of Damper Used

You need to use a backdraft damper. This is the only category of damper able to correctly regulate your bathroom exhaust system.

Backdraft Damper

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 out (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 2023-05-28 / Affiliate links / Images from Amazon Product Advertising API

Incorrect Installation

A damper must be labeled and listed, which means that it must be approved by the international and or local codes for the purpose for which you are installing it.

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.

In order to establish whether the damper is installed correctly, you may need to call in a professional to inspect the situation.

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. This might make it possible to contact the people who installed the damper incorrectly.

As it is against 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.

Otherwise, you will be able to notice if the damper is installed backward by checking whether the valve is opening towards you or away from you. It should be towards you.

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”.


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.

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 set of blades that, using a motor or gravity mechanism, will open or close. If the electrics or sealing mechanism are compromised, this may result in the blades being unable to open or close.

If the blades cannot open, then air will not be ventilated in the ducts of the ventilation system correctly.

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.

If the blades are chipped or cracked, this will affect the airtight seal of the damper and may allow leaking. Leaks will allow air to pass through the damper without being regulated the way the object is designed to control it.


If your blades are not closing or opening 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

If the seal for the damper is compromised, this means that it is no longer airtight. In this situation, the damper will no longer be able to exclude the exhausted air from the vent.

The seal can become damaged due to age, meaning it will no longer perform adequately to seal off the backdraft damper.

This can be made worse by the fact that a bathroom exhaust system often deals with moist and humid air. This damp may decrease the lifespan of your seal.

Any mold or mildew that thrives in a hot and humid environment may grow in the venting system and may grow over the seal area, which would compromise the seal. It can also degrade the seal depending on what material the seal is made from.


You need to clean the seal if there is dirt causing the seal to be compromised. Otherwise, you should be replacing your seal.

Defective, Broken, or Old Electrical Components

Some backdraft dampers are operated by motors, which means that there are electrical components to the system.

These electrical components can be defective, can become damaged and break, and can suffer from wear and tear with age. You need to replace or repair the components should this occur.

As the damper closes using an electric motor, any of the aforementioned problems will impact how the valve closes and whether or not it seals airtight. If this happens, the damper will be unable to perform its function of preventing backflow.

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


Any defective, broken, or old components will need to be repaired or replaced as is most applicable. These electrical components can be dangerous and should be replaced or repaired according to electrical codes and safety guidelines.

You may wish to call an electrician in to ensure that the electrics are safe and properly maintained.

In terms of these potential problems with a backdraft damper, the more likely scenarios are to do with damaged components instead of installation or damper type.

How to Install a New Damper

It will be helpful for you to know all about backdraft dampers and how to choose the best one for you. But in this article, let’s look at how to install a backdraft damper.

First, let’s cover three important points before you install the damper:

  • Look at your local codes to check if there are any special requirements for bathroom exhaust systems.
  • Check that the damper you have selected is listed and labeled for use in a bathroom exhaust system.
  • Make sure the damper is not damaged.

When installing the damper, ensure that you are following the manufacturer’s instructions, as this is what the IRC states as the correct installation regulations.

Your damper should not need to be squeezed into any space to be installed. It should be appropriately sized, and you should have sufficient access for the installation.

There should be nothing that could obstruct the installation or operation of the damper, nor anything that could cause damage to the damper over time.

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

Is the Smoke Coming Through the Fan?

It is important to establish whether the smoke is actually coming through the bathroom fan or not.

Sometimes, it may seem like the smoke is coming through the fan because when it is turned on, the smell appears.

However, it could be pulled into the room through a window when the fan is turned on. This is the result of how a bathroom exhaust fan works.  The fan creates negative pressure in the room, which is compensated by the inflow of air from other rooms or outside.

Yellow Streaks Could Be Caused By Cigarette Smoke

If your neighbor’s cigarette smoke has been contaminating your bathroom for years because 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.


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