Should You Use A 4” Or 6” Duct For Bathroom Fan? (Solved!)

Choosing the right duct for a bathroom fan is essential.

This can make or break how the bathroom fan functions and how it eliminates impurities in this part of the house. A lot of property owners are not careful when it comes to the installation of ducts for bathroom fans when they should be.

A common comparison is made when looking at choosing between a 4” or 6” duct for a bathroom fan.

It’s recommended to use at least a 6″ duct for bathroom fans. Anything less than this can be restrictive and reduce airflow.

by choosing the right duct, you are going to eliminate most of the long-term concerns that come with the bathroom exhaust fan. It should always have enough space for the air to flow and this won’t happen when the duct is unsafe.

Here is a look at some of the factors to consider when comparing between a 4” or 6” duct for a bathroom fan.

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Comparing 4″ To 6″ Duct For A Bathroom Fan

1. Placement of the Duct

The placement of the duct is essential.

You will want to understand how the duct is going to go through the house. For most, it is going to run through the wall and into the attic depending on where the bathroom is located.

This is one of the most important details to mull over as a property owner. In some cases, a 4″ duct might be the only option available to you due to spacing inside the ceiling or wall.

On the other hand, a 6″ duct is better as it is going to perform better for the most part. This is something to keep in mind when it comes to the underlying CFM. You don’t want the restrictive nature of a 4″ bathroom duct to get in the way of how a fan performs.

Take your time and make sure to find a way to get the duct to fit nicely.

4'' or 6'' duct for bathroom fan

2. Airflow

Airflow is going to matter a lot with this type of fan.

You are going to have a bathroom fan that is producing a set amount of power when on. This is the power that is going to generate enough suction to remove excess moisture and/or pollutants in the air.

If this doesn’t happen, the airflow is going to get restricted and that is when the smaller duct becomes a problem.

It is generally recommended to choose a 6″ duct for a bathroom fan because of the airflow. It will make the suction easier and that does matter over the long haul.

3. Electrical Output

The CFM measurement is going to play a role in how effective the bathroom exhaust fan is.

Most studies show the bathroom fan needs a larger duct. It is going to generate a tremendous amount of force when it is on and that has to match with the underlying duct.

A 4″ duct is going to work but it will be 4-5 times more restrictive than its 6″ counterpart.

This is something to take into account when choosing between ducts for the bathroom fan.

4'' or 6'' duct for bathroom fan

4. Longevity

How long is the duct going to last once it is in place?

For the most part, both ducts are going to last for a long time if they are installed by a professional. The real issues with ducts tend to involve overuse and/or placement inside the walls.

You have to make sure it is perfect and airtight for the results to be in your favor as a property owner.

However, it is likely the 6″ duct is going to last longer than the 4″. This has to do with the amount of CFM that is being produced and how much pressure it’s going to put on the ducts when the fan is running.

Final Thoughts

These are the most important variables to consider when comparing a 4” or 6” duct for a bathroom fan.

In most cases, the 6″ duct is better for a bathroom fan and is going to be compatible with the fan’s CFM rating. This is critical when it comes to choosing a duct that will be versatile, effective, and long-lasting once it’s installed.

Settling for a smaller duct is not efficient as it will break down over time.

Choose a bathroom duct that is going to tuck nicely into the wall and isn’t going to become clogged in the coming months. The 6″ duct is simply a better choice and the right way to go for those in this situation at home.

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