A bathroom exhaust fan serves the critical purpose of ventilating moisture and odors out of your bathroom. Without proper ventilation, condensation and humidity can accumulate and allow mold to grow. Breathing mold spores can cause respiratory issues for some people.
In addition to health concerns, excess moisture can cause other bathroom problems:
- Peeling paint and wallpaper
- Rotting wood
- Damage to drywall and tiles
By installing a bath fan, you can proactively avoid these issues and create a healthier, more comfortable bathroom environment.
Benefits of Installing a Bathroom Exhaust Fan
Here are some of the top benefits of adding an exhaust fan in your bathroom:
- Removes moisture – Ventilates steam from showers and baths
- Prevents mold growth by controlling humidity
- Reduces odors from bathroom use
- Improves indoor air quality
- Longer-lasting bathroom materials since less exposure to moisture
- Less chance of mildew and bacterial growth
Fan Capacity – Choosing the Right CFM
CFM stands for “cubic feet per minute” and refers to the volume of air a fan can move. Choosing a fan with the proper CFM rating is critical to getting adequate ventilation.
The general bathroom fan capacity guidelines are:
- Small bathrooms (50 sq ft or less) – 50 CFM
- Medium bathrooms (50-100 sq ft) – 80 to 100 CFM
- Large bathrooms (100+ sq ft) – 100+ CFM
Choose a CFM on the higher side of the range for households with more than 2 people or very humid climates.
To determine the exact CFM needed, multiply the room’s length x width x height to get cubic feet. Take this number and multiply by 0.13 to calculate the minimum rated CFM you need.
Step 1 – Choose an Appropriate Mounting Location
Choosing the right mounting location is key to maximizing moisture removal. Here are bathroom exhaust fan mounting guidelines:
Guidelines
- Mount over the shower or bathtub enclosure since this area generates significant steam and moisture.
- Position between the shower/bath and bathroom door to effectively draw humid air out.
- For a water closet, mount the fan near the toilet.
- Place as close to moisture sources as possible – within 2 feet ideal.
- For ceiling mounts, install the fan at least 7 feet above the floor.
- Wall-mounted fans should be installed 6 feet from the bottom of the fan to the floor.
Step 2 – Create Appropriate Venting
Proper venting to the outside is crucial for bathroom fans to work correctly. Here are the most common exhaust venting options:
Ceiling Exhaust Through Roof
This is the most popular exhaust method. The fan gets mounted to the bathroom ceiling and vents through an attic and roof exhaust vent:
- Provides shortest, most direct pipe route
- Uses least elbows/bends – improves airflow
- Attic installation may be difficult or impossible
Ceiling Exhaust Through Wall
Fan gets mounted to the ceiling and the ventilation pipe goes horizontally through the attic and out of the sidewall exterior vent.
- Avoids roof penetrations
- Vent termination is less visible from curb
- Requires navigating joists and long pipe runs
Vertical Wall Venting
Fan mounted on wall and vents vertically through vented soffit channel to the exterior:
- No need to navigate joists/attic
- Condensation in duct can drain back into fan
- Restricts future relocation of fan
For vertical soffit vents, make sure there is a way for moisture to drain out the channel to avoid backflow into the fan or bathroom.
Step 3 – Install Fan Housing into Ceiling Joists
With location and venting determined, next is securely installing the fan housing. Here is the process:
- Turn the power off at the main breaker panel. Use a voltage meter to verify. Lock out the panel and tag out the circuit.
- Measure and cut a hole in the ceiling for housing mounted between two joists. The hole should be slightly larger than the housing dimensions.
- Position the housing and trace the outline with a pencil. Drill pilot holes at corners.
- Use a keyhole or saber saw to cut the opening. Make small relief cuts if using a saber saw.
- Install hanger bars onto the housing with provided long screws. Orient the mounting tabs parallel with the joists.
- Lift the assembly into the opening—slide mounting tabs over the bottom of joists to temporarily support housing.
- Hammer nails/screws at a downward angle through tabs into joists to permanently secure housing. Install screws on both sides.
- Install ducting to the venting termination point. Use metal foil tape at all joint connections. Slope horizontal ducts downward at a 1-degree angle so moisture can drain out.
- From below, caulk gaps between the housing and ceiling with acrylic latex caulk.
The fan assembly is now ready for electrical and ducting connections.
Step 4 – Install Wiring and Connect Electricity
With the housing securely installed between the joists, the next step is wiring.
Electrical Guidelines
- All bathroom exhaust fans must be on a GFCI-protected circuit
- Use 14/2 or 12/2 nonmetallic sheathed cable
- Wire size depends on the fan’s electric rating and circuit length
Here are the step-by-step wiring instructions:
- Turn the electricity OFF at the panel. Lock out and tag out. Verify it is off with the voltage meter.
- Run wiring from the panel with enough length to comfortably reach housing.
- Secure cable using insulated staples, cable ties, or hangers with at least 8” clearance between ceiling and wire.
- Pull wires through housing electrical knockout and make connections:
- Black wire = Fan’s black “line” wire
- White wire = Fan’s white “neutral” wire
- Ground wire = Fan’s green/bare “ground” wire
- Make connections with properly sized wire nuts or crimp connectors.
- Tuck wires carefully into the housing and replace the electrical knockout cover.
With the housing mounted and wired, next is installing the exhaust fan unit itself.
Step 5 – Install the Bathroom Exhaust Fan Unit
Here are step-by-step instructions to install the exhaust fan unit into the housing:
- Carefully lift the fan unit into position under the housing with the label facing into the bathroom.
- Temporarily support the fan with a ladder or prop from underneath.
- Align screw holes on the fan housing with those on the mounting plate in the fan unit.
- From below, re-confirm proper alignment. Adjust position if necessary.
- Apply silicone caulk on top of the fan unit around the perimeter where it meets the housing. This prevents moisture from dripping into the fan when ceilings get condensation.
- Insert mounting screws into holes and tighten firmly to secure fan in place. Do not over-tighten.
- Connect plug or hardwired electrical wires from the housing into the socket in the fan’s wiring compartment if not already done.
The exhaust unit should now be fully installed and ready for testing.
Step 6 – Confirm Proper Installation and Operation
Before closing up the ceiling, verify proper fan operation:
- Turn the power back on at the panel and circuit breaker.
- Flip the wall switch to test the operation. The fan should turn on smoothly.
- Verify airflow by holding a tissue or paper under the grill. It should pull firmly.
- Turn the fan to high setting and shine the flashlight in the grill checking for flapping or movement that indicates air leaks. Caulk gaps as needed to resolve leaks.
- Listen closely to fan operation and air movement in the pipe. Volume should be smooth and consistent. Strange sounds indicate issues like loose parts, debris lodged in fan, or vent blockages. Diagnose and fix any problems.
- Turn the bathroom humidifier on high and wait 15 minutes to generate moisture. Turn on the exhaust fan to maximum speed and check that humidity gets noticeably reduced within a few minutes. This confirms adequate airflow.
- Inspect exterior ventilation outlet. Verify moisture is exiting outside and not accumulating gaps indicating a blockage.
Once proper installation is confirmed:
- Seal fan unit to ceiling with exterior grade silicone caulk
- Insulate around housing with faced batt insulation
- Install or patch drywall
- Finish decorating bathroom
Congratulations – your hard work has paid off with a brand new properly functioning bathroom exhaust fan!
Helpful Tips and Tricks
Here are some additional pointers to make your bathroom vent fan project go smoothly:
- Select a durable fan designed for bathrooms with moisture resistance certification
- Buy all necessary mounting and hardware pieces included – fewer trips to the hardware store!
- Take pictures before the removal of the old fan during the demo to reference wiring locations
- Use emerging LED light/fan combination units to upgrade lighting at the same time
- Hire an electrician if uncomfortable doing wiring
- Have extra flexible ducting and vent pieces on hand
- Carefully read the manufacturer’s instructions
- Clean up thoroughly – bits of insulation and drywall can damage the new fan
- Properly seal the vapor barrier in the attic after venting install
Installing a bath fan requires planning, precise installation, and making connections. But with this detailed guide, you can feel confident tackling this important upgrade for a healthier and more comfortable bathroom environment.