Can I Use PVC Pipe For The Bathroom Vent?

Can I Use PVC Pipe For The Bathroom Vent?

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Can I Use PVC Pipe For The Bathroom Vent?

Some buildings’ design makes it difficult and impossible to vent a bath fan to the exterior.

This presents a huge problem, especially because a home’s design might complicate the installation of proper ventilation.

Fortunately, bathroom ventilation does not present problems in all houses. It’s only hard to install proper ventilation in complex design homes.

But you might be asking, can I use PVC pipe for the bathroom vent? Yes, it’s advisable to use metal or PVC for ductwork instead of a flexible duct to vent your bathroom fan.

While flexible duct (flex duct) is inexpensive, it doesn’t perfectly venting bathroom vents.

In many homes, it will suffice to install a fan/light combination in the bathroom ceiling, then vented through the roof or a soffit or sidewall.

This is cool in venting odors and excess moisture outside. But what do you do when your building makes venting your bath fan to the exterior a daunting task?

Since many situations will always make installing a bathroom fan venting to the exterior, it is essential to employ construction creativity to solve this problem.

Additionally, it’s required to ensure smart product selection and the installation skills of a well-reputed and experienced HVAC contractor.

This has been the case since bathrooms moved indoors as ventilation was required to remove odors and exhaust excess moisture.

Anyone will tell you how much moisture can be produced by taking a hot shower.

Can You Vent A Bathroom Fan Into A Plumbing Vent?

Yes, but why would you want to try something that’s dangerous? A few years back, my next-door neighbor installed a bathroom fan in the ceiling.

Their bathroom was in the room right next to their laundry room.

His washing machine had the standard drain pipe vent of a PVC pipe that vented to the outside through the roof.

My neighbor didn’t want to cut another hole in his “precious” roof, so he connected the bathroom fan vent to hide the washing machine drain vent in the attic to vent outside.

One day, he came home only to find pieces of his house all over the neighborhood!

Although you might not be that unfortunate, venting a bathroom fan into the plumbing vent risks venting sewer gasses into your home.

Haven’t you noticed that drain vents open above the roof line or use one-way air admittance valves?

This is meant to avoid such gasses in your house. And they are unpleasant and unhealthy as well.

Still, a drain vent is usually too moist and too small to vent a bathroom fan properly.

On the other hand, your fan is designed to use a 4″ duct, and if you force it to go through a 1.5″ diameter pipe;

Lint might get pushed out by your fan and accumulate on the sides of the vent pipe, possibly blocking the pipe to the slowing of your drainage and ventilation.

Additionally, you’ll have a pretty visible issue for anyone inspecting your attic to see. This might cause problems with the local authorities. It’s best to do things the right way.

Can Two Bathroom Fans Share A Vent?

No, not exactly. Two bathrooms will not share one roof duct since it won’t work. This must be disappointing to hear, I know.

However, it’s possible to install a single fan in your attic for both bathrooms. This will make your bathroom quieter.

Indeed, you can mount one in-line centrifugal fan in the upper roof to exhaust the moisture from your two bathrooms.

As long as your two bathrooms are close together, one having an exhaust fan, the other can use the same exhaust duct.

Therefore, if you have been wondering whether you can connect a new exhaust duct into the existing one, you can’t.

If you do this, you might have a situation where the air will be blown from one bathroom to the other. Additionally, this will not be approved by building inspectors.

While you can’t get two fans on one vent, it’s possible to force a single fan and alone vent to serve two bathrooms.

Can I Use PVC Pipe For The Bathroom Vent?

As mentioned earlier, this is a setup requiring an in-line centrifugal fan to be mounted on the roof. This will be handy in drawing air simultaneously from the two bathrooms.

Get a grille in each bathroom attached to ducts, and let the latter fasten to a “Y” connector at the fan. This means that you will have a single exhaust exiting through the roof.

Additionally, mount a switch in each bathroom. And because the fan is in the roof, you will scarcely hear it.

Fortunately, special fans retail at relatively low prices (starting at $160).

However, the cheaper way is adding a fan in the second bathroom and separately venting it.

While that will necessitate cutting another hole in the roof or siding, it’s worth it.

You will also be better off installing a fan with a built-in humidity sensor that automatically detects rapid increases in humidity, such as when bathing.

On this detection, it automatically turns on the fan. This is cool as the sensor will switch off the fan after the humidity drops.

However, such fans (with the upgrade) can’t be considered cheap.

Can You Run Two Vents One Duct?

Yes, but it’s not advisable. If you do this, the upstream vent might likely blow into the downstream one unless you install back-draught shutters.

But even when you have back-draught shutters, the performance will be greatly reduced.

Additionally, the downstream one will find it hard to open when the upstream one is running simultaneously.

Indeed, forcing two fans to blow in the same duct is not easy to get working properly. I recommend a single in-line fan that sucks air from both bathrooms.

The outlets of two vents in one duct will provide not only sap performance but also pressure differences.

While nothing in the IRC particularly touches on this, inspectors will probably not pass it (I asked one who said he wouldn’t pass it if done that way).

But the number of exhaust venting to the soffit passing is enormous. 

My friend who successfully did this tells me that he occasionally gets a whiff of a dump from the other bathroom. But tying one to the attic seems more practical to me.

Alternatively, you can use a non-motorized ceiling vent, tying its 4″ duct into the already existing fan’s duct with the Y adapter.

But as insinuated earlier, the backdraft dampers will increase the resistance of the ductwork. Indeed, it might be better to move up to the next size of duct.

All the same, if both fans are on simultaneously.

You don’t have to double the size of the outlet to compensate since pressure and velocity should automatically increase to compensate somewhat.

This is because a 5″ duct is 1.5 times bigger than a 4″, which would quickly mitigate.

In my bathroom, I once did a simple setup (I can’t recommend this!). I did this setup and would NOT recommend it.

I have a 110cfm old fan in my main bathroom and an 80cfm Panasonic fan in a small bathroom.

I used cloth dampers, although each fan has its built-in damper with about a 6ft total run.

When both fans run simultaneously, the smaller fan gets overwhelmed and will not move enough air.

Do Stacking Fans Increase Airflow?

Does fan stacking live up to all the attention it gets? Not exactly!

As you might know, heatsink vendors look for ways to hype sales every once in a while and consequently come up with stacked fans.

It seems like a good idea to stack one fan on top of another. You might even be forgiven for believing the lie that it “doubles the airflow” if this is the default rationale.

But the truth is harsh. While stacked fans might work, there are certain conditions under which they must work.

Without such conditions being present, fan stacking will be useless and potentially dangerous as it dictates worse performance.

But meeting these conditions will never give you twice the airflow. Indeed, if you are lucky enough, you will get an additional 20% performance with the best conditions present.

The air that leaves the first fan’s blades comes off at about a 45-degree angle in stacked fans.

This is a potential situation for turbulence unless the second fan takes the air undisturbed at the same angle.

Otherwise, all you get is hyped turbulence and noise, with no chance for a performance boost.

To get the possible 20% performance boost, the second fan will rotate in the opposite direction. Many promoters of stacked fans ignore this essential fact.

Generally, buying a heatsink that with stacked fans is a very great deal for the vendor. Unfortunately, it’s a poor deal for the buyer. Consequently, more is not always better.

Can You Use A Flexible Duct For The Microwave Vent?

Not really. There is yet to be a mechanical code that allows a flexible duct of any material used in a domestic kitchen exhaust.

Many mechanical codes particularly forbid it. It might help to understand that there are codes that are operational where you live.

And these are things you must take note of. For instance, if you violate a code in your state, you will not be able to pass inspection scrutiny or code inspection.

And while you may bribe your way over the hurdle, it’s not a good idea. This is because you will get a higher likelihood of grease buildup and way more resistance.

This range hood is a thing that is not cherished by range hoods.

It’s indisputable that flex is quite delicate and even prone to tears. Again, it scarcely remains connected very well. I can’t even trust flex for clothes dryers.

On the other hand, a duct for a range hood needs to be smooth, double-walled, and solid. This is very similar to the requirements for a stove chimney.

The way a stove chimney should never contact anything flammable (not even the cabinet shelves), so is a duct hood.

This means that you should ensure that the vent needs to project substantially above the roof.

In my former career that lasted a couple of years.

I was constantly in the working world undertaking the actual “industry standard” fire tests of the many different building assemblies.

Can I Use PVC Pipe For The Bathroom Vent?

This has been handy in coloring my ideas pertaining to how things need to be done.

Additionally, codes are much less stringent for consumer items as opposed to ‘commercial’ applications. This is because insurance companies drive fire protection codes.

These companies are affected by losses, and it scarcely costs them much when your house burns down.

Therefore, a warehouse has tighter rules than bedrooms – even if bedrooms are where people die.

Can Gas Dryers Use Flexible Ducts?

Clothe dryer vents play an important role in home safety. Unfortunately, many people are oblivious of this important fact.

Dryer venting systems are designed to safely carry lint that is notorious enough to get past the lint filter.

This comes as an important function since over 14,000 home fire incidences involves clothe dryers every year. The leading cause of such fires is “dust, fibre, or lint.”

In addition to removing lint, dryer venting systems get rid of the hot, moist air, and the carbon monoxide generated from natural gas combustion.

As long as a dryer venting system has been constructed from appropriate material and correctly installed per code.

It will prevent fires and mold-related health problems if cleaned regularly. Still, it will be handy in preventing damage to interior woodwork. 

This is caused by warm, humid air leaking from the ductwork. Additionally, in the case of a gas dryer, it will effectively prevent carbon monoxide from leaking into your home.


It’s possible to use PVC for bathroom vents. If you use metal or PVC for ductwork, you will see better performance and avoid using flexible ducts to vent your bathroom fan.


Hi! I I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

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