How to Install a Bathroom Exhaust Fan
When your bathroom exhaust fan gets noisy, and leaves your mirrors and bathroom covered in a steamy haze, it’s time to replace it. Here are the steps you’ll need.
Skill
Advanced
Time
Few Hours
Cost
Less Than $500
What You Need for This Project
Determine Fan Size
The installation is easiest if you’re replacing an existing fan. You can use the existing switch, wires and ductwork. Also, it helps to get a fan that’s the same size as your existing fan so you won’t have to adjust the size of the ceiling hole. Use the information below to select a fan.
Fans are rated by CFMs and sones. CFM stands for cubic feet per minute – it’s a measure of airflow. The size of your bathroom can help determine how many CFMs you need. Some manufacturers recommend the number of CFMS based on square feet or cubic feet.
Length x Width = Square Feet
Length x Width x Height = Cubic Feet
Some manufacturers use the CFM formula below.
Length x Width x Height x .13 = Number of CFMs (round up to nearest 10)
For example, 8.5 ft. x 9.5 ft. x 8 ft. x .13 = 83.98 (round up to 90)
Choose a fan 90 CFM or larger.
As a general rule, small bathrooms typically require about 50 CFMs, while large bathrooms require around 100 CFMs.
If your bathroom is larger than 100 square feet, add up the CFMs for each fixture below:
- Toilet: 50 CFMs
- Shower: 50 CFMs
- Bathtub: 50 CFMs
- Jet Tub: 100 CFMs
Another factor when buying a fan is sones, which is a measurement of sound. The higher the number, the louder the fan — 2 is considered quiet.
Determine Exhaust Route
Your exhaust fan must vent outside. If the fan isn’t accessible through an attic, you’ll need to vent through a sidewall of your house. These types of ducts and vents are typically installed when the house is built. If you don’t have a duct leading to a sidewall vent, call a professional for help.
If you have access to the attic, the fan can vent either through a gable wall or roof. Letting the fan exhaust into an open attic will cause moisture buildup on the underside of the roof. Avoid venting through a soffit vent or ridge vent. The warm air will exhaust out the duct and enter back into the attic through the soffit vent or ridge vent.
Determine Electrical Options
It’s easiest to use an existing switch for your new fan. Some fans include a light, which can be operated separately with an additional switch or double switch. However, if your old fan doesn't have a light, you’ll need to install new wiring to operate a double switch.
Note: Call an electrician if you're not comfortable working with electricity.
Remove the Old Exhaust Fan
- 1
Turn off the Breaker
Turn off the breaker to the fan. Remove the grille cover and use a circuit tester to check that the power is off. Steps:
- 2
Remove Motor
Remove the motor from the housing. It might be held in place with screws. Remove the screws and disconnect the motor from the wiring. Steps:
- 3
Remove the Housing
Remove the housing. Fan manufacturers have different methods for securing the housing. Some fans are held in place by mounting screws secured to a ceiling joist. Remove the screws attached to the joist.
Other fans are held in place with metal brackets secured to the ceiling joists. If you have access to the fan through an attic, remove the screws or nails holding the brackets to the joists.
If you don’t have access to the fan through the attic, you’ll have to cut the brackets from below. Use an oscillating saw or reciprocating saw to carefully cut the brackets. Avoid cutting electrical wires and expect to touch up the ceiling drywall with spackling later. Steps:
- 4
Disconnect any Remaining Electrical
Disconnect the connections. Move the housing around in the hole so you can access the electrical and duct. Disconnect any additional electrical and pull the house wire out of the fan housing. Remove the exhaust duct from the fan too. Then remove the fan housing from the ceiling. Steps:
Option One: Mounting the Exhaust Fan with Attic Access
- 1
Adjust the Size of the Hole
Adjust the ceiling hole as needed for the fan to fit. Hold the housing up to the hole to check. If the hole is too small, trace the housing onto the ceiling then cut the ceiling with a keyhole saw. Steps:
- 2
Fill in the Ceiling
If the hole is too big, you’ll need to patch the ceiling. Cut a piece of drywall to make the ceiling hole the right size for your fan. Attach the drywall filler to a larger piece of wood, set it in the hole, and drive screws through the ceiling into the wood. The patched areas can be repaired with spackling later. Steps:
- 3
Attach the Duct Connector
Attach the duct connector to the fan housing. It should just slide in the slots. Steps:
- 4
Secure Brackets
From the attic, attach the housing brackets to the ceiling joists. Typically, ceiling joists are spaced apart 16 - 24 in. on-centre. Insert the brackets into the slots on the housing, then secure the brackets to the joists with screws or nails. Make sure the ceiling fan housing will be even with the ceiling below.
Secure the brackets to the housing with a screw, if applicable. Steps:
- 5
Connect the Electrical
Connect the electrical. Remove the wiring cover on the housing and remove the knockout plug with a screwdriver. Steps:
- 6
Connect the Fan Wires
Pull the house wires through the clamp and tighten the screws. Using quick connectors or wire nuts, connect the fan wires to the house wires matching the colours. Green is the ground and connects to the green or bare copper house wire. White is neutral and connects to the white house wire. Black is hot and connects to the black house wire.
To use quick connectors, just push the bare wire into the connector. To use traditional wire nuts, hold the two wire ends together and twist on the nut in clockwise motion.
Note: Don’t cover the connections with electrical tape unless required to do so by code. Steps:
- 7
Secure the Wiring
Push the wires into the housing and secure the wiring cover to the housing with screws. Steps:
- 8
Connect the Duct
Connect the duct. Secure a 4-in. duct to the duct connector with HVAC tape or a clamp. The duct should vent to the outside. If you don’t have an attic duct, see the installation steps later in these instructions. Steps:
- 9
Turn on the Power & Finish Up
Turn on the power and check that fan works. Some fans are extremely quiet, so listen carefully.
Install the grille by squeezing the springs into the slots and pushing the cover toward the fan. Touch up the ceiling with spackling and ceiling paint. Steps:
Option Two: Mounting the Exhaust Fan without Attic Access
- 1
Adjust the Hole in the Ceiling
Adjust the ceiling hole as needed for the fan to fit. Hold the housing up to the hole to check. If the hole is too small, trace the housing onto the ceiling then cut the ceiling with a keyhole saw. Steps:
- 2
Patch the Ceiling
If the hole is too big, you’ll need to patch the ceiling. Cut a piece of drywall to make the ceiling hole the right size for your fan. Attach the drywall filler to a larger piece of wood, set it in the hole, and drive screws through the ceiling into the wood. The patched areas can be repaired with spackling later.
Also make sure the fan can be mounted to at least one ceiling joist. If your old fan wasn’t attached to a joist, and there is a space between the joist and the ceiling hole, attach lumber to the joist to build it out next to the hole so the fan can be screwed to solid wood.
On the side of the hole opposite the joist, attach a piece of 1x lumber inside the hole. Just drive screws through the ceiling. Now you’ll have two sides to secure the fan housing. Steps:
- 3
Attach Duct Connectors
Attach the duct connector to the duct in the ceiling with HVAC tape or a clamp. Be sure to install the duct in the position specified by the instructions so the housing will line up correctly. The duct should vent to the outside. Then use a screw to secure the duct connector to the edge of the hole so that it will line up with the exhaust on the fan housing. Some manufacturers suggest securing the duct connector to the edge of the ceiling hole. Determine where it will attach the fan housing and secure it to the ceiling with a screw. Steps:
- 4
Connect the Electrical
Connect the electrical. Remove the wiring cover on the housing and remove the knockout plug with a screwdriver. Steps:
- 5
Secure Cable Clamp
Secure a cable clamp to the hole on the wiring cover. Steps:
- 6
Connect the Fan Wires
Pull the house wires through the clamp and tighten the screws. Using quick connectors or wire nuts, connect the fan wires to the house wires matching the colours. Green is the ground and connects to the green or bare copper house wire. White is neutral and connects to the white house wire.
Black is hot and connects to the black house wire.To use quick connectors, just push the bare wire into the connector. To use traditional wire nuts, hold the two wire ends together and twist on the nut in clockwise motion.
Note: Don’t cover the connections with electrical tape unless required to do so by code. You might need someone to hold the fan while you’re connecting the electrical. Steps:
- 7
Secure the Wiring
Push the wires into the housing and secure the wiring cover to the housing with screws. Steps:
- 8
Secure the Fan
Insert the fan into the ceiling hole, lining up the exhaust with the duct connector. Secure it to the wood supports with screws through the mounting flange. Steps:
- 9
Turn on the Power & Finish Up
Turn on the power and check that it works. Some fans are extremely quiet, so listen carefully.
Install the grille by squeezing the springs into the slots and pushing the cover toward the fan. Touch up the ceiling with spackling and ceiling paint. Steps:
Installing an Attic Duct with Roof Vent
- 1
Connect Duct to Fan
Pull back the insulation on the flexible duct and connect the duct to the fan with HVAC tape or a clamp. Pull the insulation back over the connection.
Tip: Use a piece of plywood over the ceiling joists as a work surface. Steps:
- 2
Trim the Flexible Duct
Hold the other end of the flexible duct against your installation spot on the underside of the roof between two rafters. Cut the duct to length with scissors or a utility knife. The wire of the duct can be cut with side cutters.
Note: Allow enough length of duct to avoid making tight bends. Tight bends in the duct can restrict airflow. Steps:
- 3
Drill a Hole in the Roof
Drill a hole through the roof with a small drill bit. Leave the bit in the roof so you can find it from the outside. Steps:
- 4
Cut a Hole Through the Shingles
From the outside, locate the drill bit. Use a 5-inch hole saw to cut a hole through the shingles and roof. It might take some time to cut through the roof. Steps:
- 5
Attach the Roof Vent Cap
Attach the duct connector to the roof vent cap. Steps:
- 6
Trace the Outline
Insert the connector in the hole, even up the cap, and trace the outline on the shingles. Remove the cap. Steps:
- 7
Secure the Roof Cap
Cut away the shingles just inside the outline following the manufacturer’s directions. Cutting inside the outline will leave a little bit of overlap of the roof cap. Apply roof cement around the hole and insert the roof cap. It should slide under the shingles. Even it up with the shingles and secure with roofing nails. Steps:
- 8
Apply Roof Cement
Apply roof cement where the shingles overlap the roof cap flange, and over any nail holes. Steps:
- 9
Attach Fleixible Duct
From the inside, attach the flexible duct to the duct connector with HVAC tape or a clamp. Pull the insulation over the connection.
Tip: To prevent the insulation from sliding down the duct, wrap the connections a few times with HVAC tape. Steps:
How To Terms
Tools, products, materials, techniques, building codes, and local regulations change; therefore, Lowe's assumes no liability for omissions, errors, or the outcome of any project. The reader must always exercise reasonable caution, follow current codes and regulations that may apply, and is urged to consult with a licensed professional if in doubt about any procedures.
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