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Can Bathroom Fan and Dryer Share a Vent

Bathroom fans and dryers both require adequate venting to exhaust air outside. Duct installations can be a challenge, especially if there’s limited room for the ducts. Killing two birds with one stone is an attractive solution, but if you really look into the matter, you’ll find that it’s not as cut and dry as this.

While bathroom fans and dryers are both useful appliances for a home, incorrect installation of the ventilation systems introduces certain hazards, such as fires. Let’s more closely examine why bathroom fans and dryers cannot share a vent and what some of the consequences would be if they did.


A bathroom fan and a dryer should never share the same vent. Building codes state that dryer vent exhaust systems must be separate from all other systems and must expel moisture out of the house through a dedicated vent. This is because of the potential hazards associated with improper dryer venting.

Why a Bathroom Fan and Dryer Can’t Share a Vent

The exhaust systems of bathroom fans and dryers are crucial, and they must be installed correctly to make them as safe as possible and to adhere to building codes and guidelines (which are in place to ensure the primary goal of safety).

There are many reasons why these appliances cannot share a vent, and it is important to understand them before attempting to install them.

Here are the most important reasons why.

It’s Illegal to Combine Bathroom Fan & Dryer Ducts

According to the International Residential Code (IRC), it is illegal to combine dryer ducts with any other exhaust systems within a house. 

Section M1502.2 of the IRC states: 

“Dryer exhaust systems shall be independent of all systems and shall convey the moisture to the outdoors.

Exception: this section shall not apply to listed and labeled condensing (ductless) dryers.”

This section of the IRC clearly prohibits dryer ducts from being combined with any other ventilation ducts or exhaust systems. This means that it is illegal for bathroom fans and dryer ducts to have a combined ventilation system.

Besides, the requirements for ventilation systems for bathroom fans and dryer ducts differ enough to making sharing more complicated than expected.

Dryer Ductwork Must Be Cleanable

As I say, ducting for dryers and bathroom fans have different requirements.

For example, flexi duct can be used for bathroom fans, but is prohibited in dryer ventilation systems, and PVC can be used for bathroom fans but is very dangerous for dryers.

One of the reasons for this is that dryers have stricter cleaning requirements.

For a dryer duct to efficiently vent exhausted air outside of the house, it must be thoroughly cleaned regularly. Keeping dryer ducts clean is also essential to prevent damage to the dryer and to keep the system running safely.

Cleaning out these ducts is essential because dryer ducts gather lint, which can develop mold, which is a health concern, and if this lint dries out, it becomes a fire hazard.

Anything that blocks the ducts will also create a risk of heat buildup, which increases the fire risk.

If the dryer duct is combined with a fan duct, dirt and debris pulled in by the fan can accumulate within the dryer duct, adding to the potential for blockage and heat buildup.

Combining the vents, therefore, makes cleaning more vital, but at the same time, it makes the cleaning more difficult.

This is because by combining them, you cause both to function less efficiently. Dirt, moisture, and lint will more likely become trapped in the ducts.

Keeping the duct and exhaust system of a dryer as a stand-alone system allows it to be easily cleaned and properly maintained.

Moist Air Can Be Released Back Into the Bathroom

The primary function of a dryer is to remove moisture from clothing and expel it outside the house. This moisture is expelled by way of the ventilation system of the dryer.

If the dryer and bathroom fan share the same vent system, moist air is likely to be released back into the bathroom if the dryer is on while the fan is off, following the path of least resistance (the shortest time spent in the duct).

Dampers can be installed to stop this movement of air, but the dampers that are used in bathroom fans are not always completely airtight, and some are less effective than others.

Thus, any moisture that collects near the fan as a result of air pushed from the dryer exhaust can leak through the fan. This may damage the fan, and water may drip directly into the bathroom, causing the following problems:

  • Mold and mildew growth – this is a common moisture-related issue, and it can threaten the health of the occupants of the house and damage paint and finishes in the bathroom.
  • Slip hazards – if the bathroom fan leaks water into the bathroom or lets in too much moisture, surfaces within the bathroom, such as a tiled or marble floor, will become unexpectedly slippery, which can be very dangerous.
  • Damp – excess moisture can accumulate as damp, which may cause significant damage to walls and ceilings, especially in the bathroom. Damp also has the potential to cause structural issues within a building, not just the bathroom.

Lint Can Be Pushed Into the Bathroom

One of the biggest problems with a bathroom fan and a dryer sharing a vent is the accumulation of lint.

Lint that is not caught by the dryer’s lint filters is expelled through the ventilation system along with the air and moisture, and if the bathroom fan shares that system, some of the lint can be pushed into the bathroom and onto the fan itself.

Over time, the bathroom fan dampers and/or blades will be covered with lint, and this may severely hinder the performance of the fan and may eventually cause the fan to stop functioning altogether.

Lint can also obstruct the damper, making it more likely that the air will just blow back in through the fan.

What Is Lint?

Lint is defined as short strands and fragments that have separated from the material, cloth, or clothing while cleaning, processing, or using these items.

These small fibers are very light and can travel easily through ventilation systems. Dryers produce copious amounts of lint during the drying process because of the combination of heat and tumbling.

Lint Is a Fire Hazard

Lint is very thin, porous, light, and dries very quickly. These attributes make it potentially flammable. This is a serious problem if it is not disposed of correctly or if it accumulates in ventilation systems. As mentioned already, this is more likely when bathroom fans and dryers share vents.

Ventilation and exhaust systems produce heat, which can ignite accumulated lint.

Bathroom Fan Pushes Moist Air to the Dryer

A problem that may not be considered when combining the ventilation systems of a bathroom fan and a dryer is moist air being pushed into the dryer by the fan when the dryer is not in use.

Moist air from the bathroom will prolong the drying process within the dryer simply because there is more moisture to extract from the appliance.

Additionally, this extra moisture in the dryer may cause the build-up of undesirable musty odors within the dryer that can be transferred to the clean clothing that is placed into it.

Won’t Pass Home Inspection (Selling the House)

For every homeowner, it is important to consider the condition of the house in case the time comes to sell the home. 

A simple, overlooked mistake, such as combining the vents of a bathroom fan and a dryer, is enough to cause a home to fail the health and safety inspection required in order for the home to be sold.

This mistake could cost the sale of the house, and rectifying it will cost valuable time in the selling process.

Insurance Could Deny Your Claim in Case of a Fire

Another important consideration for every homeowner is insurance. Insurance claims can be thrown out due to minor details, and a shared ventilation system between a dryer and a bathroom fan is one such detail.

In the case of a fire, the shared ventilation system between the two appliances could cause an insurance claim to be denied due to the build-up of lint and other flammable materials within the system and because this setup is an IRC violation.

Venting dryers and bathroom fans together is one of the most common bath fan code violations.

Dryer Venting Checklist

The ventilation system of a built-in dryer has specific requirements to be up to code, safe, and to perform at optimum levels. 

This is a checklist of the important aspects of dryer venting to follow when installing a domestic internal dryer:

  • Dryer exhaust should be vented according to manufacturers’ instructions.
  • Dryer exhaust systems must be separate from all other ventilation systems.
  • Dryer exhaust must not be placed within or near insulation.
  • A vertical riser must be included for cleaning out the system.
  • All dryer ventilation ducts must lead outdoors.
  • Makeup air must be provided if more than 0.09 m3/s of air is extracted by the dryer in one room.
  • All dryer ducts must be made from metal with a smooth surface on the interior.
  • Dryer ducts may be no longer than 25 ft.

All domestic dryer systems must be built to these specifications to comply with IRC Section M1502 and to be safely used within a home.

Printable dryer venting checklist

Related article: Can a Gas Dryer Be Installed in a Bathroom

Can Two Dryers Share One Vent?

We have established that a dryer cannot share a vent with a bathroom fan, but can two dryers share one vent?

Two dryers cannot share one vent. The stipulation in the IRC about independent ventilation applies per dryer, not per appliance type.

If one dryer is operated without the other, some of the air is pushed into the room through the unused dryer.

Can Two Bathroom Fans Share One Vent?

Two bathroom fans can share one vent. Think about bathrooms fans in apartments—they can all link up to the same vent.

However, there are some specifications required to make it possible.

For two bathroom fans to share one common vent, the fans must be of a similar capacity, or one fan will overpower the other and cause a backdraft within the system.

Both fans must have backdraft dampers installed to optimize airflow and keep all of the air moving in the right direction.

The size of the exhaust vent that the fans use must be increased by one inch for every fan that shares the same vent.

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