How To Vent Bathroom Fan Through Gable

Do you see spotting and mold growth on your walls? Is the humidity in your home making you uncomfortable? Or have the recent power bills been bothering you?

The answer to all these problems is ventilation.

Often people focus on installing air conditioning and elaborate ventilation systems in every room but ignore the bathroom. This can lead to many problems, especially in the summers when it gets hot and humid. Unventilated bathrooms and attics cause bacterial growth to multiply and increase your expenses by causing mold damage.

Good ventilation is helpful for people living in temperate and cold areas. The winters here allow for condensation, increased mold growth, and ultimately a massive dent on the homeowner’s pocket. 

If you are concerned about potential damage to your beautiful home or are mortified by your energy bills, investing in bathroom fans can save you a lot of trouble. 

To make your life easier, we have gathered in one place all the dos and don’ts of venting bathroom fans through a gable.

What are Gable Vents?

Gable roofs are easy to spot and are typically found in regions with colder climates. If your roof has two sections slanting in opposite directions to meet at the top, you have a gable roof.

The wall running underneath the intersection, forming a triangle at the top, is the gable wall. If you’ve checked the boxes so far, then congratulations, you are likely to have gable vents.

Traditional gable vents sit elegantly on the exterior of the gable wall. Also known as louvered vents, they come in pairs. Although, you may have more based on the number of gables in your house. These vents are exclusively designed for bathroom fans.

Bathroom Fans

Like any other ventilation fan, a bathroom fan sucks in the hot, humid air from the area, replacing it with fresh air. As long as the bathroom fan runs, the heat and humidity are easily controlled.

What Is The Proper Way to Vent a Bathroom Fan Into a Gable?

Ever wondered why your bathroom fan isn’t stopping the mold from forming? Well, that’s probably because of incorrect installation. To make the best out of your bathroom fan, you need to make sure the vent is positioned directly outside, secured with a hood cover.

The hood of the vent should be equipped with a flap. This flap will usually remain shut so that no dust can enter. However, it will remain open when air is blowing through it.

The flap is an absolute necessity. For days when you don’t want outdoor air coming into your home, you can count on the flap stopping it. It also prevents birds from nesting in the venting system. 

Essential Things to Consider for Installation

CFM Rating

The first thing homeowners should consider is the CFM rating printed on the back of the fan. All bathroom fans are rated on the cubic feet of air they can mobilize in a minute.

This value will vary depending on the area that needs ventilation. Depending on this, the bathroom fan which best fits your requirements can be easily selected. 

To find out the CFM of a room, take the room’s measurements in square-foot and multiply this value by 1.1. Most bathroom fans range from 50-110 CFM, although some are specifically designed for larger areas and have greater CFM values.

Venting Area

The most radical mistake one could make while venting bathroom fans is by allowing them to vent inside the house. This is most common when these fans are allowed to vent into the attic.

Your venting system is causing mold damage to your walls and your roof. If this is the case, you need to get ready for some heavy-duty repairs.


Another frequent mistake encountered with venting systems is not paying attention to leaks. This problem presents itself when the technician is doing a lousy job and the owner doesn’t pay attention. 

If your fan vent has leaks, then sadly, it is not going to work very efficiently. Additionally, these leaks are letting hot, humid air leak inside your home, ultimately defeating the purpose of the ventilation you are trying to achieve.

Installation Errors

An incorrectly installed hood cover can also send you down a rabbit hole of problems. It is crucial to ensure your hood cover is appropriately sealed. If not done correctly, the dust build-up will potentially cause choking in various points of your ventilation system. What’s worse is that this will become an easy entry point for all the flies and mosquitos nobody wants inside their house.

Duct System

One lesser-known factor that contributes to molding is the use of the wrong duct system. Ideally, an insulated duct system should be used. Using an uninsulated duct system increases the odds of condensation occurring in winters. It is always recommended to evaluate what duct system works best for your home.

Installation of a bathroom fan through a gable and creating an efficient venting system is a rather complex task. One that requires creativity and a good knowledge of how ventilation systems work since all homes are different and there is no one size fits all.

Vent Covers

Every venting system has two basic types of vents: register vents and return vents. Register vents remove stagnant indoor air, while return vents draw in fresh outdoor air. Both types of vents are equipped with covers specifically designed to ensure optimum airflow.

These covers come in various designs and colors and are made from multiple materials, from polished wood to light aluminum. Some even have the added functionality of maintaining indoor air quality by removing impurities.

Vent covers require maintenance annually. However, in some localities, more frequent sessions may be necessary depending upon the level of built-up. Clean vent covers not only improve the overall appearance but also drastically improve the effectiveness of ventilation systems.

A Step-by-step Manual for Installing a Bathroom Vent Fan Through a Gable

Drill a reference hole where you want your fan to be located

This is preferable between the toilet and the shower. But you can modify this according to your personal preferences. 

Make this bore with an extra-long, 3/8-inch-diameter spade bit. Go to the attic and remove all insulation around the hole and determine your fan’s position. Position the vent fan directly between the two joints of the reference hole. 

Plan your installation by considering all obstructions or pipes near your reference hole.

Mark an Outline

Return to the bathroom to measure the internal dimensions of the inner port—Mark the approximate area where you will need to drill into the ceiling.

Using your reference hole to transfer the measurements from the attic to the bathroom ceiling, draw a rectangular outline for the intake port. It is best to make use of a framing square or layout square for this purpose.

Cut the intake-port hole.

Uses protective gear for this step. Make sure you have gloves, goggles, and a respirator on, along with proper sawing equipment.

Cut right through the ceiling along the reference lines. The rectangular cut-out should be able to prevent most of the debris from falling off.

Carefully Position the fan

Make your way back to the attic and attach a 90° duct elbow to the vent fan housing outlet port. Make sure the elbow faces upwards.

Secure it in place with foil duct tape.

Fan and Joist Attachment

Extend the brackets to contact the joists, securing each with a single 1.5-inch drywall screw. Secure one end of the flexible duct to the elbow, which you have attached to the housing. This flexible duct is one of the components of the sidewall cap. Feed the electrical cables through the connectors and tighten them with a crew.

Cut a Hole Through the Side Wall

Select a point on the sidewall within 6 feet of the vent fan. This is where the flexible duct will exit the house. Take reference measurements and use them to mark a hole on the siding. Use a 4-inch saw to cut it out.

Attach the Wall cap and the Exhaust Duct

From inside the attic, stretch the free end of the flexible exhaust duct to the outside wall. Be careful while stretching to prevent any damage. Secure it with foil duct tape to the wall cap’s connector duct.

Install the Wall Cap

Use foil duct tape to secure the connector duct to the wall cap. Slide the wall cap into the duct hole—fit cut-outs of the foam-rubber gasket into any gaps between the siding and the wall cap.

Fix these in place with a silicone adhesive. Next, use 1.5-inch stainless steel screws to secure the wall cap against the siding firmly.

Wiring and Connections

From inside the bathroom, unscrew the blow motor and built-in receptacles. Match similar colored wires to those of the electrical cable fed into the housing in step-5. Carefully wrap and tighten a bare copper wire under the green grounding screw inside the housing.

Screw the electrical Receptacle and blow the motor back in place.

Fit the Grille

Hold the grille close to the ceiling. Slowly, slip the mounting wires into their respective slots in the fan housing. Press it tight into the roof until it fits in place. Turn on the fan for a test run.

How much does it Cost to Install a Bathroom Vent Fan Through a Gable

The total costs of equipment and labor can be anywhere between $200-$500. The equipment is relatively cheap and will probably be covered under $100. A large chunk of the investment is the labor cost.

A well-ventilated house is an investment worth your while. It will reduce how much you have to spend on repairs and power bills. In addition, it is a sustainable and cheaper alternative to expensive air conditioning and heating systems.