A plumbing roof vent is very important for all houses as it removes the house’s sewage. The sewer gasses get released through this vent, thus improving the air quality inside the house. Generally, the plumbing vents pass through the roof, but is there no other way?

It is common for the plumbing vents to pass through the roof, but it is optional. Other alternatives include running them through exterior walls, installing air admittance valves, and loop venting. It would be best if you run the vent above the roof level of your house. 

The local code for the plumbing vent goes 12 feet away from the wall. You have to check with your local building code for installing any alternative. This article will share the other alternatives to running the plumbing vents and step guides for their installment. 

What is a plumbing vent?

A plumbing vent is a system with pipes connected to the house’s P-traps. It leads to the vent stacks that pass through the roof. 

All roofs cannot handle the passing of the plumbing vents, especially if your house is old or the roof is not stable for the pipes.

The builders and house owners sometimes want the plumbing vents to pass through the walls outside the house. 

A plumbing vent is mandatory because the exhaust having the sewer odors won’t exit without the vent. 

The plumbing vent passing through the roof is seen poking outside the roof directly above your house’s bathroom and connected to the water systems.

Why do you need a plumbing vent?

A plumbing vent in the house removes the wastewater and other wasters. 

The drainage and vent utilities work together to allow the full plumbing system to work efficiently. 

The drainage pipes remove the waste from your house to a septic tank or the local sewer. 

The vent pipes allow fresh air to enter each plumbing fixture of your house. 

The vent pipes help move the water through the pipes every time the sink gets drained or the toilet is flushed. 

The plumbing vents also stop the sewer odors from entering your house and allow the wastewater and gas to escape. 

If you do not have plumbing vents, the odors enter your house and fill it with bad smells, which can further harm your health. 

Generally, the plumbing vents are located on the house roof, away from the air conditioners and windows, for the stenches can dissipate easily. 

Common types of plumbing vent pipes

While installing a new plumbing vent, you need to get the right one for your house. Some good plumbing vents are:

• True vents: The vent is common with a vertical pipe hooked to the drain line. Since no water runs through it, you can vent it from the roof.
• Common vents: The vent can be used between 2 fixtures on opposite sides, like back-to-back sinks connected to a stack with the sanitary cross. 
• Re-vent pipe or auxiliary vent: The vent is connected to the plumbing fixture or drain line. The vent runs over the main vent on the roof. 
• Air admittance valve: It is a valve that opens when the wastewater starts draining. The valve allows air to come in and blocks the gas from entering the house with the help of gravity. This vent is for multiple fixtures. 

Does the plumbing vent pipe have to be through the roof?

Plumbing vents passing through the roof only are optional. 

There are other alternatives. 

However, the vents passing through the roof are the common installation process. 

You can also run the plumbing vents through the exterior walls, but you must ensure that the vent pipe extends above the roof. 

Install the vent pipes on the outside walls without letting them pass higher than the roof. 

You must ensure the pipe is taller than the highest window of your house. 

All the house owners cannot reach the roof due to the house structure. 

So, passing through the exterior walls is an alternative to roof venting. 

Sometimes people run the vents and end up in the attic, but that is uncommon. 

Another good alternative is installing an air admittance valve or AAV. 

It can stop harmful chemicals from entering your house through the attic. 

Another one is loop venting. 

Here the vent connects to the P-trap and stands straight until it forms a loop and goes down the drain. 

Loop venting is not allowed in all the zones. 

So, you must consult the building codes before installing them. 

How to install plumbing vents through the exterior walls?

You can vent through the exterior walls instead of the roof. 

Before you start doing it, consult with the local codes to ensure that this method is compatible with your zone.

Contact the building department to get ahold of the codes. 

Now, let’s learn how to install a plumbing vent through the outside walls. 

Step 1: Cut the drain pipe

Find and see the P-trap for cutting. 

The cut must be within the 5 feet range of the P-trap. 

Use a hacksaw for cutting and carefully cut the drain pipe. 

Step 2: Sand the pipe ends

Once you have finished the cutting, you need to smoothen the cut ends. 

Use 120-grit sandpaper for $3 to $5, and sand and buff each cutting end of the pipe. 

Sand the ends until both sides of the pipe’s cut portion becomes smooth and even. 

Step 3: Install 

You need to fill up the space where you have cut the pipes with the sanitary tee. 

The sanitary tee will cost around $2 to $8. 

Before filling the cutting ends with the sanitary tee, make sure that it fits in the pipe, and you can leave an open outlet pointed upwards. 

Step 4: Extend the vent pipe 

Maintain the pipe slope around 1/4th inch towards the slope and extend the pipe upwards. 

Extend the vent pipe until you reach the point from where the pipe will pass through the wall and let it stay there. 

Mark around the vent pipe on the wall at the place where you want it to pass through. 

Make a hole with a saw in the wall, around ½ to ¾ inches bigger than the actual pipe’s size. 

Push the vent pipe through that hole that goes out of the exterior wall. 

Ensure a full foot clearance between the wall and the vent pipe. 

Step 5: Seal the pipe

Come back to the hole through which you passed the pipe. 

Install a pipe strapping along the wall and tie the pipe to it. 

Put the pipe strapping in multiple places to be safe and careful. 

Apply spray-foam insulation to the ½ to ¾ inch of extra room between the vent pipe and the wall’s hole and let it expand. 

After the insulation expands, dries out, and cures itself, remove the excess foam around the hole. 

How to install an air admittance valve?

If the local guidelines of your region allow you to install an air admittance valve or AAV instead of the roof vent pipe, you can install it. 

AAVs are mechanical, and they work in gravity’s way. So, there will rarely be anything wrong here. 

AAVs can support multiple vent lines, but they are mostly used as alternatives to vents. 

AAVs are widely available and used, costing around $13 to $30. 

Here are the steps to install an air admittance valve. 

Step 1: Find the P-trap 

Find the P-trap first. 

It will have a little loop connecting to the drain line into the sanitary tee and then to the drain. 

Step 2: Attach the PVC drain line

Measure the length of the PVC drain line at the same size as the sanitary tee and attach it. 

Make sure the PVC sits well. You can use a threaded PVC line for a good seal. 

Step 3: Put in the air admittance valve.

Locate the sanitary tee leading to the drain. 

That is the spot where you have to place the air admittance valve. 

If this valve sits vertically without obstructions like stored materials, everything will remain up to the code in maximum zones. 

How to install loop venting?

Loop venting is the most simple method and alternative to roof venting. 

You need a looped pipe going above the P-trap and down the drain. 

Here are the steps:

Step 1: Install the P-trap

You must install the P-traps under the floor if your sinks are island sinks. 

Reverse the P-trap by 180 degrees. 

It will support the flow of water to go into the trap. 

Step 2: Direct flow

Slope the drain by pointing it downwards. 

Point the vent upwards and hook the old vent after the loop. 

It will make sure the old venting is pointing down to the drain. 

This maneuvering of the old pipes will create a loop, thus the name loop venting. 

Your drain has become a vent now, and it does not have to go through the roof. 

The reason behind this loop is that it can go down and be made to use the existing pipes maximum times. 

What problems can arise with the plumbing vent pipes?

Sometimes when the plumbing vents work poorly, the whole drainage system of your house will also stop working. 

The signs that the plumbing vents and drainage system have stopped working are:

• Standing water in the sink or bathtub
• Gurgling noises
• A slow-moving drain. 

It could be due to the clogged vents due to dirt and debris. 

Blockages in the plumbing vents will create too much pressure on the drainage pipes, interrupt the water flow, and lead to leakages. 

Sometimes, you may get rid of a clogged drain, but the problem remains if the main reason is a blocked vent. 

Suppose you cannot clear the drainage using a drain cleaner, plunger, or auger. 

In that case, you are dealing with severe clogging, for which you may have to call professionals. 

It will cost around $270 to unclog the vents by the professionals. 

If the problem stays, the condition will worsen, and your house will get filled with sewer odors. 

Should I cover the roof plumbing vents?

It is a great idea to cover the plumbing vents. Your house and the vent can benefit in multiple ways.

Safety 

The vent remains on the rooftop, which means it is exposed to severe weather outside. 

The vent can get clogged by dirt and debris. 

If the problem stays long, your house will have bad sewer gasses. 

Unclogging the debris by experts will cost $270. 

So, it would be best to cover the vents to remain free from such issues. 

It will also keep animals away from your vent. 

Some of them enter and start making nests, which can be a sanitary issue. 

Prevents mold

Covering the vents sometimes encourages mold. 

But uncovered molds are more prone to mold formation. 

The rainwater and moisture will remain trapped inside the vent and encourage mold. 

Mold removal can be difficult and expensive. 

If you ignore it, it will become unhealthy for the house members, especially people with allergies. 

Covering the vent can save you from such issues. 

Reduces noises

Noise can be annoying for both you and your neighbors. 

Sometimes the vent creates disturbing noises. 

Covering the vent will reduce this noise and keep you and your neighbors happy. 

Prevents leakage and reduces pressure

Clogged vents create pressure and pressure fluctuations. 

Too much pressure in the vent can cause the water to back up, causing leaks and other expensive damages. 

The sewer odors, too, start entering your house. 

A vent cap on the plumbing vent will prevent clogging and stop the pressure and leaks. 

Vent stack caps will prevent dirt and debris from entering the plumbing vent and the system and help regulate the pressure. 

Increased durability 

Uncovered vents last for 10 years because they have to deal with the outside’s harsh environment, like heat, cold, winds, and rain. 

Covering the vents will keep them safe from such conditions to some extent and increase their lifespan. 

Covered vents will last up to 15 to 20 years. 

How far should a plumbing vent pipe stick out of the roof?

The International Plumbing Code, or IPC, recommended that the vent pipe is at least 6 inches above the roof level per section of 905.5. 

Sometimes, it is recommended to maintain at least 12 inches for weather protection. 

If you use something else for weather protection, terminate 7 feet above the roof. 

The vents must extend about 24 inches above the roof in snowy regions. 

Final thoughts

A plumbing vent pipe passing through the roof is not the only option. 

But it is the most common method of running the vent. 

Other alternatives to the roof vent include:

• Installing the vent pipe through the exterior walls.
• Considering loop venting.
• Installing an air admittance valve. 

Before considering the alternatives, consult with the local codes of your region to know which one applies to your zone.

It is good to cover the plumbing vents. 

It can protect the vent from clogging, reduce noise, prevent leakages, and increase lifespan. 

While installing the plumbing vent through the roof, make sure to install it at least 6 to 12 inches above the roof level. 

During the older days, bathrooms only had one small window. But nowadays, exhaust fans are an important part of bathrooms, and it’s impossible to imagine one without an exhaust fan. But what is the purpose of this exhaust fan, and what does it do? 

Exhaust fans in the bathroom can benefit in multiple ways. The bathroom exhaust fans will improve the air quality, control smell, and humidity, prevent the wall paints from decaying, and stop mold formation. The exhaust fan also circulates air and makes you feel fresh and cool. 

Installing a bathroom exhaust can take time, but it is worth the time and effort as it eliminates hot moist air and bad odors. In this article, we will discuss the functions of the exhaust fans in the bathroom, how it works, and things to consider while choosing one. 

How does a bathroom exhaust fan work?

A normal bathroom contains a sink, light fixtures, vanity, mirror, faucet, shower, and an exhaust fan. 

Having an exhaust fan may feel fashionable and nice, but that is not the only purpose of adding an exhaust fan. It has way more benefits. 

It helps to keep the bathroom clean and hygienic. 

These exhaust fans are connected and wired to your house’s electrical current, just like a light fixture. 

When you turn on your wall switch, the fan will start working after some time. 

The bathroom exhaust fan will start moving the interior air out of the bathroom through a vent duct or a flexible tube to the outside. 

The vent duct will then transfer the air through the roof or an exit vent on the sidewall of your house. 

The duct will remain closed through the cover plate on the vent’s exit when you do not need to use it. 

Maximum building codes will recommend installing a bathroom exhaust fan for new house constructions or remodeling. 

In California, exhaust fans with humidity and motion sensors are mandatory for the bathroom under title 24. 

These exhaust fans will operate when the humidity level is too much or it meets a sensor notes motion. 

These features must pass the inspection, and the installation and other aspects must meet the building code requirements. 

The fan size will depend on your bathroom’s square footage so that it can give adequate ventilation. 

Even if your building codes do not speak about the compulsory addition of exhaust fans, having one can improve the air quality and benefit in multiple ways. 

What does a bathroom exhaust fan do?

As I said, bathrooms used to have only open windows in the old days, which was enough. But not anymore. 

Without an exhaust fan, your bathroom will face several difficulties. Exhaust fans can help in many ways. 

In this section, we shall learn what an exhaust fan can do for your bathroom:

Humidity and mold control

Humidity is a very common problem in bathrooms. 

It does not matter whether you take a hot shower daily or occasionally because the humidity is always natural and a problem in the bathroom. 

If the humidity level gets uncontrollable, your bathroom will develop mold and mildew in no time. 

Mold can develop several health issues. It is very dangerous for people with allergies.

Once your bathroom starts developing mold, it will start growing rapidly in no time. 

Exhaust fans can control the humidity and mold development in the bathroom. 

Exhaust fans’ introductory job is to control the humidity level of the bathroom. 

The quality of your bathroom exhaust fan will control the humidity and stop mold from developing. 

Once you install a good-quality exhaust fan in the bathroom, you can see what it can do. 

You will not see any fog on the mirror or humidity in the bathroom. 

Odor control

You will try to control your bathroom’s odor by cleaning it daily and spraying multiple odor sprays. 

But you can only control the smell fully if you install an exhaust fan. 

The bathroom will have a very disgusting smell due to the frequent use of toilets. 

An exhaust fan can control and help escape this smell from the bathroom. 

But without the fan, you won’t be able to get rid of it despite frequent cleaning and odor spray. 

If you have properly installed an exhaust fan, the next person visiting the bathroom will have a better experience. 

Fumes removal

When you clean the bathroom, you might use cleaners that contain several dangerous chemicals. 

Inhaling these chemicals can harm your health and badly affect children, old people, and lung patients. 

An exhaust fan will help escape the fumes and smell of these chemicals and keep your bathroom safe. 

Modern exhaust fans contain various good features like humidity sensors, adjustable timings, lights, etc., which can ensure more bathroom safety. 

Gives comfort

During the summer, a bathroom is one of the hottest spaces in the house. 

Exhaust fans will help circulate the air in your bathroom and keep your bathroom comfortable. 

It will release the hot air, bring in fresh and cool air, and make the space comfortable. 

Keeps the wall paints in place

When the humidity level of the bathroom increases, it not only encourages mold but also decays the bathroom’s paint.

Over time, the paint starts peeling off the bathroom’s wall. 

If you do not care about it, the increased moisture level will damage the tiles, tubs, floors, etc. 

It indicates an early replacement of insulation and structure underneath and unnecessary expenses. 

Installing an exhaust fan will keep the humidity in control and reduce the moisture level. 

It will further help keep your bathroom’s wall paint in place and other things in good condition. 

Aesthetics

Peeling of the paint and decay in the wall surfaces of the bathrooms will make your bathroom look unattractive and give you a feeling of disgust. 

Installing an exhaust fan in the bathroom can control the humidity and moisture level. 

So it will keep the paint, insulation, and wall designs in place. It means the exhaust fan will maintain the aesthetics of the bathroom. 

Efficiency

A hot shower can make the bathroom mirrors and windows hazy due to the increased humidity and hot air. 

When you are in a hurry, fogged-up mirrors are an issue. 

Exhaust fans can reduce the humidity, clear the air in the bathroom faster and quite efficiently, and you can get a clean mirror every time. 

Illuminates the bathroom 

Most of the exhaust fans in recent days come with additional light fixtures. 

The lighted exhaust fans will offer better ventilation and give you extra illumination in your bathroom. 

As a result, you do not have to add extra light fixtures to your bathroom.  

The design of these modern exhaust fans will offer a stylish and functional bathroom, maintaining the aesthetics. 

What to look for in a bathroom exhaust fan?

There are various types of bathroom exhaust fans available in the market. 

You can get them with multiple styles and features to suit your house’s aesthetic. 

Some exhaust fans have sensors that turn on the fan when the fan detects humidity levels. 

Some fans have timers that shut off the fan automatically once the extra humidity has escaped. 

You can also find exhaust fans with light fixtures, heat lamps, Bluetooth, and speakers. 

But along with these, you must choose exhaust fans depending on your needs, like performance, durability, and safety. 

If the exhaust fan does not work, there is no point in adding one in the bathroom. 

Performance

While buying and installing an exhaust fan in the bathroom, make sure it fits according to your bathroom’s square footage. 

You cannot depend on the exhaust fan’s size to understand its ability. 

You must read the manufacturer’s recommendations on the label to understand the capacity.

It would be best not to go too far while selecting the exhaust fan capacity. 

If you select an exhaust fan with high capacity, it will create negative pressure and affect the air circulation and furnace ducts. 

So, you must choose the fan according to the size of your bathroom. 

Noise control

Loud noises are too annoying. 

Sometimes, the bathroom exhaust will create irritating and loud noises, especially in houses with many occupants.

Get fans with fewer noises. Check out the label’s product description and consult the seller before buying one. 

Check the customers’ reviews to gather ideas about how it reacts to daily operation. 

Durability 

The exhaust fan you get for your bathroom has to be durable because you don’t want to spend money frequently on it.

A good quality and long-lasting fan will prevent humidity and mold formation in the bathroom efficiently in the long run. 

Durable fans will be made of high-quality materials for a longer lifespan and backed up with a warranty. 

Review the installation needs and customers’ points of view to ensure the model’s capacity. 

Safety 

You will connect the exhaust fans to the electrical system of your house. So, safety is crucial. 

The fan will operate in a space with lots of water and moisture. 

So, be careful about its safety. 

To determine the fan’s safety, look for models having ETL (Electronic Testing Laboratories) and UL (Underwriting Laboratories) certifications. 

Products with these certifications will be a standard ones with good safety measures. 

Once you have installed the fan, run it once during or after the shower to check its functionality. 

If the fan works properly, it will keep your bathroom free of excess moisture and humidity and smell fresh. 

When should you turn on the exhaust fan?

The right time to turn on the bathroom exhaust fan is every time you shower. 

After that, you must leave the fan switched on for at least 15 to 20 minutes after showering. 

Keeping the exhaust fan on for some time will free your bathroom from moisture, mold, and foggy mirror. 

If you do not use the fan properly, the steamy shower can damage the bathroom’s wall and plumbing due to increased moisture levels and mold. 

The paint will start peeling off the wall, the wood will start rotting, and the drywall will become soft. 

How to choose the right exhaust fan for your bathroom?

Based on your bathroom’s configuration, you can choose any one of the standard types of exhaust fans from the following:

• Ceiling mount: One of the most common types of exhaust fan for the bathroom that exhausts through the duct in the attic to the vent outlet mounted on the rooftop.
• Inline exhaust fan: The fan is installed in a remote area, for instance, the attic, and connects to the intake duct terminating in a grille on the bathroom ceiling. 
• Wall-mount or window-mount fan: You can mount this fan if your bathroom has any exterior walls, eliminating the need for long ducts. You can install it in the window just like in the air conditioner. 

What size of exhaust fan will be suitable for the bathroom?

The Home Ventilation Institute or HVI suggests a ventilation rate of 8 air exchanges per hour for the bathrooms. 

The exhaust fan capacity is measured in cubic feet per minute of CFM. 

It has a 1:1 relationship with the bathroom’s square footage, up to 100 square feet. 

A 70 square feet bathroom will need an exhaust fan with 70 CFM, and a 50 square feet bathroom will need a 50 CFM exhaust fan. 

The minimum exhaust fan size must be at least 50 CFM. That is the smallest one available. 

Bathrooms bigger than 100 square feet will need an exhaust fan with more CFMs. 

The HVI recommends the following exhaust fan capacity for the bathroom with multiple occupants:

• 50 CFM per toilet
• 50 CFM for a shower
• 50 CFM for regular bathtub
• 100 CFM for a jetted bathtub

If you choose an exhaust fan smaller than the bathroom’s square footage, the bathroom will not be properly ventilated. 

So, it cannot control the humidity or improve the air quality. 

An oversized exhaust fan is fine, but make sure the exhaust is not with very high capacity. 

Otherwise, that can have negative pressure on the bathroom. 

You can choose an oversized exhaust fan if the ceiling is above 8 feet. 

Also read: What Type Of Ducting For Bathroom Fan?

Is an opening window better or an exhaust fan?

An open window stands nowhere beside an exhaust fan. 

Suppose you keep a window open during the rain. In that case, it will simply increase the moisture and humidity level of the bathroom, therefore encouraging mold and mildew. 

On the contrary, an open window will increase the energy bill when you keep it open during the cold. 

The cold air will enter your room through the bathroom window, for which you have to increase the heater of your house and end up with high energy bills. 

Though having an open window is wonderful as you can look at the outside nature, you won’t have the courage to open it most of the time. 

So, an exhaust fan is way better than an open window. 

Final thoughts

Bathroom exhaust fans are an integral part of the bathroom, especially in recent times. It helps prevent high humidity, moisture levels, and mold. It controls odor and fumes from different chemicals and supports good air circulation. 

It further helps keep the paint of the bathroom’s wall intact and maintains its aesthetics. While choosing the right exhaust fan for your bathroom, consider certain factors, like performance, noise control, durability, and safety. 

You must also consider the size. The exhaust fan’s size should fit with the square footage of your bathroom. The right time to run the exhaust fan is when you start a shower and switch it off at least 15 to 20 minutes after showering. It will reduce moisture, mold, and foggy mirrors. 

In old times, the bathrooms had no fans but an open window for ventilation. But nowadays, ventilation fans are an important part of the bathroom. While installing a bathroom, choose the right ducting type for venting.

You can use three types of ducting for the bathroom- rigid, flexible, and PVC ducts. A common way to duct the bathroom fan is by using rigid ducts for the main duct and a short length of flexible duct to connect the bathroom fan and the main duct. Generally, Round ducting is the ideal choice.

Venting is important for bathrooms. So, knowing the different duct types will help you choose the right one. This article will guide you about the different ductwork designs and their benefits and drawbacks. So let’s begin without further delay. 

Flexible duct

Flexible ducts are a good way to reduce the cost of ducting. 

Flexible ducts are easy to install and have a longer lifespan. 

Most people consider using flexible ducts over rigid ones. 

Though this duct has pros and cons, the benefits overpower the drawbacks, which is why they are preferred the most. 

The building code approves flexible ducts for the bathroom. 

Chapter 15 of the International Residential Code, or IRC, Section M1504, mentions that one can use ‘flex ducts’ in their table for the allowed duct lengths.

Flex ducts are flexible ducts.

Flexible duct materials

Flexible ducts are made up of plastic, fiberglass, or metal. 

Avoid using cheap aluminum ducting materials, as they can tear easily. 

It is common for the aluminum ducts to tear at the installation time only. 

After a few years, you can find duct tearing while investigating the moisture damage in the attic. 

Find ducts will have good and protective layers on the top of the aluminum, for example, PVC-covered aluminum ducts. 

They are tear-resistant and easy to insulate and install. 

One good option is Heavy-duty AC Infinity Flexible Aluminum Ducting, heavy-duty 4-layer protection, 25 feet long for Heating and Cooling, Ventilation, and Exhaust. 

The product contains a 4-layer design and is more resistant to leakages, ripping, and cuts. 

You can couple this duct with a spring-loaded and rubber-sealed backdraft damper for long-lasting and quiet ventilation, for example, AC Infinity 6” Backdraft Damper with Spring-loaded Folding Blades for 6” ducting in Range Hoods and Bathroom Fans.

Duct length

The length of the flexible duct has to be around 1.5 meters or 5 feet. 

A lot of people are seen using very long flexible ducts. 

They start using it from the bathroom to the exterior walls. 

Over time, the duct will squeeze and become saggy. 

Do not use very long flexible ducts for the bathroom fan. 

If the duct becomes saggy, it prevents airflow and drops the local code requirement rates. 

Size the flexible ducts based on your bathroom ventilation requirements for enough ventilation. 

You can use the flexible duct from the bathroom to the exterior walls if the bathroom is near the exterior wall and the distance is below 5 feet. 

Benefits of flexible ducts for bathroom fans

One of the most visible benefits of flexible ducts is their flexibility. 

• You can place the duct over a more confined space easily. 
• You can bend the duct and follow the angles which the rigid ducts cannot follow without using joints and extra attachments. The curve of the flexible duct is better than the rigid’s sharp corner.
• Another great benefit of using flexible ducting is its cost. Even if you buy high-quality flexible ducts, the cost will be much less than the rigid metal ducting. 
• You can also save on the labor cost of installing flexible ducts because it is easier and takes less time. 

Drawbacks of flexible ducting

The ducting in the bathroom should carry the warm moist air out and let fresh air enter. 

It will further prevent moisture buildup, mold, and mildew. 

Despite having so many benefits, there are some disadvantages of using flexible ducts:

Increased friction

The ridges on the inner corner of the flexible ducts can cause airflow turbulence. 

This turbulence will increase so much that the air particles will crash with the duct walls and increase friction. 

Friction further increases the airflow pressure through the duct. 

The airflow pressure must be enough so that the air moving through the duct can carry the air and moisture until the air is released outside. 

The airflow pressure and duct efficiency will reduce when the friction increases. 

The inner walls of the ridges will trap and retain moisture instead of letting them out. 

The lower the airflow pressure, the easier it will be for the moisture to remain in the ducts. 

Sagging duct

A flexible duct will sag if they are not given proper support. 

The sagging will affect the smooth airflow, increase friction, and lower the pressure. 

It can also gather water which the duct should take outside.

Since flexible ducts can retain moisture, you must clear them very often, making them a high-maintenance duct. 

You can’t use range hoods.

It is also not recommended to use range hoods for the flexible ducts. 

According to the IRC chapter 5 Exhaust Systems, Section 505.3 Exhaust Ducts, the domestic cooking exhaust will discharge through the sheet metal ducts made of galvanized steel, stainless steel, and aluminum or copper. 

Such ducts have smooth inner walls.

Flexible ducts are not made of metal sheets; therefore, they do not have smooth inner walls. 

Can I use insulated flexible ducts for the bathroom fan?

Flexible ducts can be both insulated and uninsulated. 

You can either buy a pre-insulated duct or insulate it after buying. 

However, pre-insulated ducting is difficult to cut. 

So, consider the project nature before you select a duct. 

If any extra part is difficult to cut, do not keep the extra ducting part curled in the attic. 

That will reduce the efficiency of the system. 

Make a little effort to remove that extra part. 

A better option would be to buy an uninsulated PVC-covered duct. 

Install it first, then insulate it with a cotton duct wrap for better results. 

Rigid duct

Rigid ducts are also considered the best bathroom fans because of their performance in ventilation. 

The IRC has also not mentioned anything about using rigid ducts.

They have mentioned the term ‘smooth-wall ducts’ in their table for the allowable duct lengths. 

The rigid ducts are considered smooth-wall ducts. 

If your bathroom has range hoods, you should only use rigid ducts made of galvanized or stainless steel ducting. 

This ductwork is good for bathroom ventilation fans with a square or rectangular duct connection. 

The exhaust vent is also connected straight to the rigid duct. 

Benefits of rigid ducting

• Rigid ducting is made of stainless steel metal sheets and has a smooth inner wall. 
• The smooth inner walls create less turbulence than the rough inner walls of the flexible ducts. 
• As a result, there is very less pressure loss inside the ducts. 
• Since the inner walls are smooth, there is less moisture retention of buildup inside the ducts. 
• The rigid ducts are low-maintenance, do not require frequent cleaning, and have a longer lifespan. 

Drawbacks

Though it is considered better than flexible ducts for bathroom fans, people still prefer flexible ducts over rigid ones. 

Here are the reasons:

Expensive

Rigid ducts can be very expensive compared to flexible ducts. 

Even high-quality flexible ducts are less expensive than rigid ducts. 

Besides, you need extra joints, adapters, and attachments to install them, which further increases the expenses. 

It is more expensive because installation requires special skills, which increases labor costs. 

Due to this cost, pure rigid ducting is rarely seen. 

Difficult to install

Installing a rigid duct for the bathroom fan is very difficult. 

It will require professionals. 

Moving it is more difficult if you have already installed it and later realize that you did something wrong. 

So, make sure that you have it properly installed. 

Whatever you do must be final. 

Cannot bend them

Unlike flexible ducts, you cannot bend rigid ducts. 

You must use elbows and joints to move them around obstructions and turn corners. 

The more elbows and joints you use, the more turbulence it causes, which is more than the flexible ducts’ turbulence. 

Noise

Rigid ducting will make a lot of noise than flexible ducts. 

The noise from other rooms and outside too gets transferred by these ducts. 

That is why the flexible duct is used for some feet of the duct run.

PVC ducts

Polyvinyl chloride or PVC ducts are also good for bathroom vents. 

A PVC duct is generally a PVC pipe. 

If your bathroom is close to the exterior wall, you can use round PVC ducts for the bathroom fans. 

Some bathrooms also use straight PVC pipes to vent the bathroom fans. 

However, these ducts are not seen bending. 

The connection side of these ducts also needs flexible ducts. 

So, you can use PVC ducts instead of pure rigid ducts. 

PVC ducts are cheaper than rigid ducts. 

You may see such venting procedures in most places due to the local authority. 

So, check it to confirm that you can approach this process locally. 

Can I use a rigid and flexible duct combo for bathroom fans?

A combination of rigid and flexible ducts is the most common type used for bathroom fans. 

Both residential and commercial bathrooms have this combination. 

The design is great for bathrooms located far away from the exterior walls of the building, where the distance is around 15 to 25 meters. 

If you have a long rigid duct as the primary duct for the bathroom fan, you can use 1-2 flexible ducts at shorter lengths below 1.5 meters.

It will connect the bathroom fan and the rigid duct and between the rigid duct and the external grille or vent/ louver. 

The combination is quite useful because the rigid ducts have smooth inner walls, which prevents moisture retention. 

Connecting the rigid duct directly to the bathroom fan will cause a rattling noise. 

The flexible ducts will absorb the vibration and reduce the noise. 

The exhaust fan is connected to the flexible duct. 

The flexible duct is then connected to the rigid duct. 

The grille type will be up to you, but use a plenum box as an adapter. 

It will allow flexible duct connection. 

Some people use two flexible duct connections for more exhaust airflow. 

You can use two small ducts for good results. 

The same setup is also used for public bathrooms with more exhaust fans. 

The flexible ducts are always connected to the rigid ducts with the duct collars. 

The duct collar is an adapter that connects the flexible duct with the rigid one. 

You can also use round ducts instead of square or rectangular shapes. 

Since the flexible ducts are not smooth inside and become saggy, you should only use them for distances up to 1.5 meters. 

If your bathroom is 1.5 meters away from the exterior ways, combine the rigid and flexible ducts for your bathroom fan. 

Should I insulate the ducts for the bathroom fans?

It is very important to insulate a duct. 

Otherwise, water will condense inside the duct and drip down from the bathroom fan. 

Insulating the duct will prevent condensation and water dripping. 

It will also create brown stains around the fan. 

An insulated duct also creates excessive heat loss through the bathroom fan.

You can use a cotton duct wrap to insulate your ducts.  

A good product for the cotton wrap is Frost King CF55 Foil Backed “No Itch” Natural Cotton Duct Wrap, 12-Inch x 1-inch x 15 feet.

Also, place the insulation above the bathroom fan to prevent heat loss. 

Bathroom fan duct specifications

Bathroom fans can be humid and corrosive. 

So, the rigid ducts must be made of galvanized iron or better. 

The ducts should be made following the SMACNA (The Sheet Metal and Air Conditioning Contractors’ National Association) standards. 

The wall thickness of the duct should be 0.5 mm.

Additionally, you must choose the duct size according to the bathroom and fan size. 

Check the bathroom fan’s external static pressure to make sure it has enough strength to release the air outside the house. 

Layout

The layout for the bathroom fan ducts comes in two types – the side of the house and the roof. 

Most of the time, the ducts are run on the side of the house with weatherproof grilles or vents. 

A bathroom vent system has an exhaust air vent on the ceiling. 

The air vent consists of a plenum box connected to the flexible duct, which is again connected to the rigid duct. 

Before the rigid duct joins the ventilation fan, it remains connected to the flexible duct.

The other end of the ventilation will stay connected to the flexible duct, which will again be attached to the rigid duct. 

The rigid duct will run to the outer walls of your house to meet the external vent for the exhaust air release at the side of the house. 

Add an insect screen to the external vent to prevent pests and insects from entering your house. For example, MVM 125S Metal Vent Grille By Vents-US.

Some people consider using a dryer duct for flexible ducts to duct the bathroom fans. 

For example, Omony Dryer Vent Hose 4-inch 5FT Flexible Dryer Ducting Tube Air Duct Aluminum Insulated Hose Kit Indoor Outdoor. 

If you cannot do the side layout, consider running the duct through the roof.

Cover it by some elbow or bend it to prevent rainwater from entering the duct. 

Always insulate your duct after installation. 

Duct size

The 4-inch or 6-inch ducts are the common duct sizes for bathroom fans. However, it depends on the fan capacity. 

If the fan housing has a 6-inch connection, use a 6-inch duct, even if the fan contains a 4-inch adapter. 

If the duct length is over 25 feet, install a 6-inch duct, no matter the fan size. 

Can the bathroom fan and dryer use the same outside duct?

Avoid using the same duct for the bathroom fan and the dryer. 

According to the IRC, Chapter 15, Section M1502.2 Independent Exhaust Systems, the dryer exhausts and ducts must be separate from other systems. 

So, you need to install a separate duct for your dryer. 

Some best ducts for the bathroom fan

• Dundas Jafine BPC425R6 Insulated Black Jacket 4”x25’ Flexible Insulated Duct R6.
• Hon&Gyan 3-Inch Dryer Vent Hose, 16Ft, Flexible PVC Air Ducting for HVAC Ventilation Fan. 
• HVAC Premium 4”x20’ – Round Duct Sheet Metal Pipe – 30 Gauge Galvanized – Crimped End Connection [10 pcs 2’]
• AC Infinity Flexible 6-Inch Aluminum Ducting, Heavy-Duty Four-Layer Protection, 25-Feet Long for Heating Cooling Ventilation and Exhaust. 

Final thoughts

Two main types of ducts for bathroom fans are rigid and flexible. 

Flexible ducting is preferred over rigid ducting due to easy installation and low cost. 

But you can’t use flexible ducts for longer distances.

Some people prefer rigid ducting because their inner walls are smooth, which does not retain moisture and is good for longer distances. 

But installation is very difficult and costly.

For better results, you can use both ducts together. 

Another good option is PVC ducts instead of rigid ducts. 

Insulate your ducts after installation. 

You can also get pre-insulated ducts, but insulation after installation would be better. 

FAQs

How far should you vent the bathroom?

It depends on the fan’s airflow rating and the duct’s diameter and type.

Can I vent a bathroom fan through the soffit?

There is generally no problem venting the fan through the soffit, especially if your roof has a few holes. 

But it is completely up to the house owner. 

Most people prefer it due to the short route, preserved roof integrity, no back-drafting, and room heat retention. 

How to choose the bathroom fan?

To choose the bathroom fan, find the CFM of the fan, locate a good area, and find a suitable fan type. 

Measure the cutout dimensions, find the right duct size, and consider the noise level. 

In today’s date, bathrooms with exhaust fans are a must. While selecting an exhaust fan, you want to avoid buying the wrong size or type. The right fan size should be able to remove sufficient humidity and bad air from the bathroom without creating annoying noises. 

The exhaust fan size for the bathroom depends on the bathroom’s square footage. Your bathroom needs 1 CFM per square footage, and the fan should support 8 air changes per hour. A 50 to 110 CFM fan is common in most bathrooms, but it may change depending on your bathroom size.

Understanding the CFM value is crucial when determining the right exhaust fan size for the bathroom. This guide will share how to determine the right exhaust fan size for different bathroom sizes, factors to consider, and a few tips about installing a fan. 

How to determine the exhaust fan size for the bathroom?

The CFM, or cubic feet per minute, is a unit that determines the exhaust fan size for a bathroom. 

The fan’s power is measured in cubic feet per minute. 

Generally, the bathrooms will require at least 1 CFM per square footage. 

An exhaust fan must be strong enough to fill the bathroom with fresh air every 7.5 minutes or 8 times per hour. 

For example, if your bathroom measures 80 square feet, you need a fan with 80 CFM. 

Let’s understand the calculation with an example.

Suppose you have a bathroom with 10 feet by 10 feet and an 8 feet ceiling. 

So, you need to multiply the bathroom’s length, breadth, and height and then divide the value by 7.5 to get the right CFM fan for the bathroom. 

So, 10x10x8 = 800

800/7.5 = 106.67

So, for a bathroom measuring 10 feet by 10 feet and 8 feet in height, you need an exhaust fan with 106.67 CFM. 

What is the standard size of the exhaust fan for the bathroom?

Bathroom exhaust vents are generally rated by how much air they can move, measured in cubic feet per minute. 

The standard fan sizes are good for most bathrooms, measuring 100 square feet or less. 

The rule of thumb is 1 CFM per square footage. 

If you have a bathroom measuring 54 square footage, you need an exhaust fan with 54 CFM. 

Sometimes, experts recommend installing a slightly oversized fan, for example, a 60 CFM fan for a 54 square feet bathroom. 

The minimum fan size for the bathrooms is 50 CFM. 

So, if you have bathrooms measuring below 50 square feet, for instance, 42 square feet, you need to install an exhaust fan with 50 CFM. 

While selecting the exhaust fan size, you must consider the duct size. 

Most 50 CFM exhaust fans will require at least a 4-inch round duct. 

The higher the CFM, the bigger the duct size, for instance, a 5 or 6-inch duct. 

What factors determine the size of the exhaust fan for the bathrooms?

While selecting the right bathroom size, you need to consider a few factors, like:

• Large bathroom with many occupants 
• Tall ceiling
• Bathroom with an enclosed space. 

These factors will affect the exhaust fan size; thus, the size will keep changing. 

Here is a brief about how these factors can change the exhaust fan size:

Large bathroom with many occupants

The formula to calculate the exhaust fan size is the same as before. 

You multiply the length, breadth, and height and divide the value by 7.5. 

For bathrooms measuring more than 100 square feet, you have to jump to an oversized exhaust fan, for example, a 100 CFM exhaust fan.

Some larger bathrooms have multiple occupants, like bathtubs, jetted tubs, etc. 

In that case, you need to find the CFM needed by each occupant to determine your bathroom’s exact exhaust fan size. 

The common occupants include: 

• Bathtubs need 50 CFM
• Jetted tubs need 100 CFM
• The shower needs 50 CFM
• The toilet requires 50 CFM

So, if your bathroom has only a shower and a toilet, you need a 100 CFM exhaust fan. 

If your bathroom has jetted tubs and bathtubs with toilet and shower, you need a 200 CFM exhaust fan. 

Tall ceilings 

Generally, most of the bathrooms have 8 feet ceilings. 

But some larger bathrooms have a ceiling above 8 feet, like 10 or 11 feet. 

In that case, the calculation and fan size will change. 

Sometimes, some standard-size bathrooms also have higher ceilings. 

An 80 square feet bathroom with 8 feet ceiling, then an 80 CFM fan is fine. 

If the ceiling measures 10 feet, you must consider the fan size. 

Here is how you calculate:

Multiply the square footage by the ceiling height, i.e., 80 square feet x 10 feet = 800.

Then, divide the number by 60 (minutes in one hour), i.e., 800/60 = 13.33, rounding up to 14. 

Now, multiply the number by 8 (8 air changes per hour), i.e., 14×8 = 112

So, for an 80 square feet bathroom with 10 feet ceiling, you need an exhaust fan with 112 CFM. 

That is how you determine and calculate the exhaust fan size for your bathroom. 

Bathroom with an enclosed space

Some larger bathrooms have enclosed areas for closets, shower spaces, or a toilet. 

If your bathroom is one such kind, you must buy an extra small exhaust fan.

Since these areas are enclosed, they will have individual doors. 

So, it can be challenging for one exhaust fan to provide adequate air circulation to two different sections. 

If your bathroom has an enclosed shower space, you will also need a GFCI (Ground Fault Circuit Interrupter) outlet. 

These outlets trip off when moisture enters the outlet. 

It is their way of avoiding dangers like short circuits. 

Most of the bathroom closets have exhaust fans with lights. 

So, you can also get one for your bathroom closet. 

Coming to the size of the exhaust fan for the enclosed space, you can select a small exhaust, like a 50 CFM. 

An enclosed area will be a small space, so the minimum size of the fan will be fine for such spaces. 

Some house owners do not want to add an extra fan for the enclosed spaces in the bathroom. 

Besides, it can increase energy bills. 

There will be no serious problem if you do not add a second fan. 

In that case, you need to keep the door of the enclosed space partially open for adequate air circulation and to let bad air escape. 

It will make a primary vent fan. 

How should you deal with the fan’s noise rating?

Once you have decided on the right fan size for your bathroom, you need to consider the sound rating. 

The sound and the fan size have a one-to-one relationship. 

An oversized exhaust fan will create very loud and weird noises. 

Besides, it also puts negative pressure on the bathroom. 

To understand the right sound rating, you need to know the sone rating to measure the loudness. 

A quiet fan is a valuable investment to keep the bathroom peaceful and calm. 

Exhaust fans with lower sone numbers will be quieter, and higher numbers will have loud noises. 

A sone rating of 1 is the quietest of all. 

Here are a few sone ratings to help you find a suitable fan for your bathroom:

• 1 sone rating is equal to a refrigerator’s humming and whispering, which is around 29 decibels. 
• 2 sone rating is similar to the ambient sound in the library, around 38 decibels. 
• 3 sone rating is similar to the sound of a low conversation with 44 decibels. 
• 4 sone rating will equal the sound of a television, measuring 48 decibels. 
• 5 sone rating equals the sound of moderate rainfall, around 51 decibels. 

These sound ratings can help you find the amount of noise a fan can make. 

What happens if I get an undersized or oversized fan?

Sometimes, house owners get an undersized exhaust fan so that the bathrooms can have quiet noises. 

When you get a powerful exhaust fan that suits your bathroom, it does not mean it will create loud noises. 

The amount of noise an exhaust fan makes while operating is rated in sones. 

Most bathroom fans will have noise ratings between 0.3 to 4, 4 being the loudest. 

Suppose you have chosen an undersized fan because it has a rating below 1. 

In that case, the fan won’t be able to ventilate your bathroom properly. 

As a result, your bathroom will have humidity and bad air despite having an exhaust fan. 

So, always choose the exact one. 

Similarly, an oversized fan is also not good and puts negative pressure on your bathroom. 

Too much oversized will create loud noises. 

It can be slightly oversized. For example, to remain safe, you can get a 60 CFM fan for a bathroom measuring 54 square feet. 

What if I do not replace the exhaust fan?

Some house owners do not want to replace their undersized exhaust fans. 

If you do not have to change it, there are a few other options to deal with it. 

You can install a fan timer mounted in the place of the switch. 

It will let your fan run for a limited time, like, 5-10-15-30 minutes. 

Next, you can install a humidity-sensing fan control. 

A switch will turn on automatically when the humidity gets too high and shut off when the humidity level reduces. 

You can keep your bathroom door open partially, install a freshener, or have an open window high up. 

Types of exhaust fan for the bathroom

There are two types of fans, exhaust fans, and ventilation fans. 

The exhaust fan helps release the bad air out, and a ventilation fan brings fresh air. 

If you want to have an exhaust fan, you can choose from the following type:

• Ceiling mount fans: These exhaust fans are the popular ones for the bathroom, and it works by connecting to the exhaust duct above the bathroom. 
• Wall mount: These fans are used when your bathroom cannot have ceiling mount fans. These fans will vent directly outside without any exhaust ductwork. 
• Inline fans: These fans are installed in a remote space and tap into the ductwork of the attic. A grille in the bathroom ceiling will connect to the system. 
• Window mount: You can use this fan by inserting it just the window-mounted air conditioners. 

How to install a bathroom exhaust fan?

A window fan that works when you plug it inside the wall receptacle will not require installation. 

But you must install a GFCI outlet. 

Installing a fan is quite challenging as it requires cutting a hole in the wall and then sealing it after everything is finished. 

You may deal with some electrical wiring if there is no plug. 

The ceiling mount fans are more complicated to install.

Here are the steps to install a bathroom exhaust fan in the ceiling:

Location

You can install the exhaust fan in the ceiling if you have one bathroom with no enclosed areas. 

If your bathroom includes a toilet and shower, place the fan between the toilet and the tub or shower. 

Plan the duct route

The duct has to be straight and short to pass through the attic to the roof or the sidewall. 

If your house has no attic, the duct should pass between the ceiling joists and involve drywall removal. 

Cut holes

Find two locations. 

One location will be to cut a hole for the fan in the ceiling. 

Another location will be to cut a hole for the exhaust vent in the roof or sidewall. 

If you have a separate water closet, find a small exhaust separately. 

Install the fan and the exhaust vent.

Once you have cut holes, you must install the fan and the vent. 

Secure the fans to the ceiling joists with braces. 

The exhaust vent will be attached to the roof deck or the sides with appropriate flashing. 

Connect the duct

A flexible duct is suitable for the bathroom exhaust fan. 

Clamp it to the fan and the exhaust vent. 

Hook up the fan to power.

Wire the fan to the wall switch. 

Connect it to your house’s electrical system by tying it to the outside circuit. 

Otherwise, you can also install a new one for the fan with a separate circuit breaker. 

Door clearance

While installing the fan, ensure the bathroom door contains about ¾ inch of clearance from the floor. 

It will let the air enter to replace the sucked-out air and put less stress on the fan. 

Fan options

Four types of fans are ceiling, window, inline, and wall. 

But these fans also come in various types, like only the fan, fans with light, etc. 

So, if you want to increase the aesthetic of your bathroom, here are some options:

• Fan only – For a small retrofitting bathroom, you can use a 50 to 70 CFM fan costing around $15 to $50. 
• Fan and light combo – This fan is good for small bathrooms or water closets. The cost will be around $30 to $150. 
• Deluxe combo – The fan includes various features – fan, light, heater, nightlight, timer, and a humidistat. The humidistat will turn on the fan automatically when the air moisture increases. The cost will be $150 to $600. 

Final thoughts

There is no exact fan size. 

The right exhaust fan size depends on the square footage of your bathroom. 

As a rule of thumb, a bathroom will need 1 CFM per square foot. 

The exhaust fans should be strong enough to vent the bathroom every 7.5 minutes or receive 8 air changes per hour. 

For example, an 80 square feet bathroom needs an 80 CFM exhaust fan, provided the height remains 8 feet. 

The exhaust fan size will change based on factors like the height, the bathroom with multiple other occupants, and an enclosed area. 

If the height is more than 8 feet, the size will increase. 

For larger bathrooms with multiple occupants, add up the required CFM for each occupant and then calculate the CFM of the bathroom. 

You need an extra fan if your bathroom has enclosed areas like a closet, toilet, or shower. 

Otherwise, keep the door partially open to let it work as a vent. 

FAQs

Will the CFM get affected by the duct size?

The quality and size of the duct can affect the bathroom’s CFM. 

For a 3-inch duct, if you buy an exhaust with 130 CFM with a 6-inch duct, the appliance will not work well. 

Will the exhaust fans be very powerful?

Yes, they will be powerful, so you must choose an exhaust fan whose size suits the bathroom’s size. 

Oversized fans will create disturbing noises, and undersized fans will not serve the purpose.