How To Vent A Bathroom Fan Through Soffit (Detailed Guide)

Are you interesting in how to vent a bathroom fan through a soffit?

Bathroom fans are usually vented to the side wall or to the roof, but sometimes venting it to the soffit is preferable. It isn't always a good idea to put a hole in the roof.

In this guide, I will go over...

  • The steps required to vent a bath fan to the soffit or eave
  • Benefits of installing a bathroom fan to the soffit instead of the roof
  • Why an insulated vent hose is always preferred

Let's get started with this guide!

how to vent bathroom fan through soffit

What Is A Bathroom Fan Through Soffit Install?

The soffit is the underside portion of the roof overhang or eave. Most of the times when a bathroom fan is vented to the soffit, it is because it isn't feasible to install it to the roof or side wall.

For one, if it is a DIY install, you may not want to go onto the roof. You may not want to make a hole in the roof that may start leaking in the future (especially if you have had roof problems).

In addition, for a second story bathroom, it may be a significant amount of work to vent it to the side of the home --- and may require going down (and making a 90 degree bend). You also may not have a gable wall in that area near the bathroom.

Sometimes bathroom fan soffit vent fan is the easiest solution because you have easy access in the attic and you don't have to climb onto the roof.

Soffit Exhaust Vent Cover

The soffit cover does the same thing as vertical wall-mounted bath vent covers—they keep out exterior air, moisture, and birds. I can't even tell you how many birds nests I have seen in vents.

My favorite soffit exhaust vent is made by a company named Dundas Jafine.

The Dundas Javine vent cover is spring loaded so it will properly seal when you turn off the fan. It is also adjustable so it can fit a 4-inch or 6-inch duct.

You can view the price of the Dundas Jafine cover on Amazon right here.

Read Also: The Best Quiet Bathroom Exhaust Fans (Almost Silent)

How To Install The Soffit Exhaust Vent?

Avoid Dips In The Hose

You want to install the soffit exhaust vent cover in a straight line (as much as possible) from the bathroom exhaust fan. The less number of turns and bends means it will have more air flow and just work better.

In addition, bends or dips in the bathroom vent hose may accumulate water (condensation) in the low parts.

Verify Proper Vent Hose Size

If you are going to be installing a new duct (rather than moving the existing) then you may want to verify the duct size that your bathroom fan uses. Many higher powered bathroom fans use larger duct sizes such as the 4" or 6". Most of the older bathroom exhaust fans are still using the smaller 3" ducts.

Some bathroom soffit vent covers have adapters already installed for 4" 5" or 6" ducting.

Cut The Soffit Hole

When you install the soffit exhaust vent, make sure it is in the right location, between the rafters (or roof lookouts) and mark the area with a permanent marker. The soffit vent cover manufacturer usually includes a paper template that you can use to draw the hole on the soffit.

After you marked the hole with a permanent marker, you can begin to cut out the soffit with either a jig saw or tin snips.

Once you have cut out the hole, you will need to place the vent hose to that location in the attic if you haven't done so already.

bathroom fans exhausting to outside

Connect Hose To Cover

Now you just have to pull the vent hose through the cut hole, and pull it out about a foot. It is at this time when you may want to cut off extra vent hosing in order to have a straight line from the bathroom (without dips in the hose).

Now you should connect the vent to the soffit cover using a metal clamp, tighten the screw with a phillips or flathead. After you installed the clamp, you can cover it with foil tape to make sure it is extra snug and won't come off.

Insert the vent cover back onto the soffit.

Use the screws that came with the vent cover, and mount it to the soffit with a cordless drill or with a manual screwdriver. You may also need to drill pilot holes for the screws.

Read Also: The Best Bathroom Exhaust Fans With Humidity Sensors (Automatically Turns On)

What Type Of Bathroom Vent Hose?

Most older bathroom fans like the ubiquitous Broan 688 uses the older 3" duct hose. However, a lot of the newer bathroom fans recommend using the 4" 5" or even 6" duct hose. Check with your manufacturer as to which vent hose to choose.

You can still use a smaller diameter vent hose with new bathroom fans, but there will be reduced performance and the rated specs won't be the same. Some soffit exhaust vent fan covers have adapters already installed for 4" 5" or 6" ducting.

Like if your bathroom fan has a 4" outlet, but you want to connect it to a 3" or 5" hose, there are plastic adapters that you can buy to connect it together. It is still recommended to go with the manufacturer recommendations if at all possible.

Insulated Vent Hose

If your attic is not sealed off such as if there is foam insulation or if it is unfinished --- then I always recommend installing an insulated vent hose.

You can buy these vent hoses that already have insulation installed on the outside.

An insulated bathroom vent hose will help prevent condensation (water) forming on the outside of the vent in the attic.

Insulated Flexible 4" Duct (25' Long)

During the cold of winter, your attic air will be as cold as the outside. And when you run your bathroom vent, it is sending conditioned warm air through that vent hose in the attic to the outside.

Read Also: The Best Bathroom Exhaust Fans With LED Lights (Extra Light Fixture)

Water forms when two different temperatures meet --- similar to how when you take an iced lemonade outside on a hot day... water will bead on the outside of the glass.

The same thing happens when the attic is very hot, and the indoor air is cool as in during summer. An insulated vent hose will prevent these potential water problems and the subsequent mold growth that may develop.

Since the air in the attic isn't fully air-sealed, if mold forms in the attic, those mold spores can be circulated throughout the interior of the home. The mold and water can also damage the structural wood in the attic.

It's also important to reiterate that bathroom fans should be vented to the outside

I have been on many home inspections where the owner, builder, or contractor was too lazy to vent the bath fan to the outside.

Read Also: How To Vent A Bathroom Exhaust Fan Through An Attic (My Detailed Guide)

poor install of bathroom fan vent in attic (1)

What's The Bottom Line On Soffit Exhaust Vent Installs?

Installing a bathroom exhaust fan to the soffit can likely be done within an hour or two if you have all of the tools such as the vent cover, a tall ladder, the vent hose, vent clamp, and jig saw.

Even though the exhausting bathroom fan may disrupt the intake air flow of soffit venting, it is a very small area and isn't going to be a big problem.

The ease of installation with attic access and avoiding the roof is a major advantage to installing a bathroom fan to the soffit.

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company (read his full bio on the About page). To ask Arie a question, please use the comment box at the bottom of the relevant article.

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Home Inspector Secrets is an online resource for owners, buyers, and sellers to understand all aspects of home maintenance. We have detailed home guides, product reviews, inspection advice, and much more.