If you want to learn how to vent a bath fan through a soffit, you are on the right website!
In this guide, I will go over...
- 4 simple steps to install a soffit vent cover
- Benefits of venting to the soffit instead of roof
- Why install an insulated vent hose
As a home inspector, I have seen numerous poorly installed exterior vent covers — and soffit vents are no exception.
If a soffit hood is poorly installed, it may lead to moisture and mold problems inside of the attic or on the underside of the eaves. And even though bathroom fans are usually vented to the side wall or roof, venting to a soffit is sometimes preferable.
Keep reading to learn about venting your bathroom fan through a soffit!
What You Need To Know About Venting A Bathroom Fan Through A Soffit?
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 installing a bathroom fan to the soffit is the easiest solution because you have easy access in the attic and you don't have to climb onto the roof.
There are also a few other alternatives for bathroom fan venting if don't want to use the soffit (or don't have one).
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.
How To Vent A Bathroom Fan Through A Soffit (4-Step Guide)
- Install The Duct As Straight As Possible
- Use The Right Sized Duct For Your Exhaust Fan
- Cut The Soffit Hole In The Right Location
- Connect The Bath Fan Duct To The Soffit Cover
Step 1 - Install The Duct As Straight As Possible
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.
Step 2 - Use The Right Sized Duct For Your Exhaust Fan
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. Check out my guide on the best ducts for bathroom fans here.
Some bathroom soffit vent covers have adapters already installed for 4" 5" or 6" ducting.
Step 3 - Cut The Soffit Hole In The Right Location
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.
Step 4 - Connect The Bath Fan Duct To The Soffit 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 >> What Are All My Bathroom Fan Venting Options?
How To Pick The Bathroom Duct When Venting Through A Soffit?
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.
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.
Should My Bathroom Vent Be Insulated?
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. You can read my guide on bathroom vent condensation here.
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.
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?
Final Thoughts On Venting A Bathroom Fan Through The Soffit
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.
And 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.