721 How To: Install a Bathroom Fan

How To: Install a Bathroom Fan

How To: Install a Bathroom Fan

Replace your noisy bath fan with a super quiet model.

Bathroom fans don’t have to sound like a jet engine to remove enough air to keep your bathroom mold- and odor-free. In fact, a loud bath fan may signal just the opposite: inefficiency. The latest bathroom fans are so quiet you can barely hear them run, yet they remove just as much air (if not more) than your old rattle trap—and they’re more energy efficient, too. Whereas most homes at least 20 years old have bathroom fans that consume about 125 watts of energy and rate 5 to 6 sones (roughly five times the noise of an average refrigerator, which rates only one sone), today’s options range from a $100 fan that uses around 55 watts and rates 1.5 sones to a super quiet 0.3-sone model that uses just 5.8 watts for around $200.

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Updating your bathroom fan to a new model means you can run it longer to remove more humidity and still save money on your energy bill, all without the nuisance of an obnoxiously loud roar. Don’t delay on for fear of complication; this guide for how to install a bathroom fan will set you on the right course.

Getting Started: Selecting Appropriate Size and Style

Bathroom fans come in several sizes, from small units that exhaust just 50 cubic feet of air per minute (CFM) to larger units that remove almost 200 CFM. Choosing the proper fan size from this wide range is critical to your family’s safety. A fan that’s too small won’t remove enough odor or moisture, and one that’s too big can create a dangerous negative air pressure situation that pulls deadly carbon monoxide back through your furnace or water heater flue.

To calculate the size that will meet your needs, multiply the bathroom’s length times its width and height to arrive at total cubic feet. Then multiply the total cubic feet by .13 and round up to the nearest 10. For example, a 9 ft. x 7 ft. bath with an 8 ft. ceiling equals 504 cubic feet. When you multiply 504 by .13, you get 65 CFM, so round up and buy a 70 CFM bathroom fan. However, if you have a large bathroom (600 cubic feet or more) or one with a jetted tub, it’s best to bump fan size by 50 CFM.

Quieter fans cost more, so invest in one that fits your budget. If you have a mold problem in your bath, you may also consider a model with a built-in moisture sensor that runs the fan until humidity drops to a normal level. Choose a “retrofit” model with slightly larger dimensions than your current fan for easiest installation. Retrofit models can be installed from inside the bath, saving you a trip into your attic, and a larger footprint eliminates any need to patch the wall.

How To: Install a Bathroom Fan


– Retrofit bathroom fan
– Work light
– Extension cord
– Screwdriver with flat and Philips bits
– Voltage tester
– Stud finder
– Tape
– Pencil
– Drywall saw
– Reciprocating saw with metal cutting blade
– Cardboard (optional)
– Selfdrilling 1.5inch construction screws
– Driver drill and bits
– Aluminum foil HVAC ULlisted tape
– Twiston wire connectors
– Fire caulk
– Firerated expanding foam


Before you begin any removal or installation, turn off the power to the bathroom fan at the circuit breaker. Don’t rely on just the switch to cut power to the fan. Use a work light and extension cord to light up your work area.


If the grille on your bathroom fan doesn’t have screws or a knob, pull it straight down to access the “U” shaped spring retainers. Squeeze the top two legs of the spring together and lean the legs towards the center of the fan to unhook them from the housing. Repeat the procedure on the other spring and remove the grille.

Then disconnect the fan by unplugging it from the receptacle in the fan housing (if equipped). Probe the receptacle with your voltage tester to make sure the power is off. If the fan is hard wired, double check the power by placing the tester leads in the hot and neutral wire connectors before removing them. If you detect power, stop and call an electrician. As long as the power is off, you can remove the fan retaining screw. Then, tilt the fan down and out.


Use a stud finder to locate the rafter or truss in the bathroom ceiling or a stud in the wall that’s nearest the existing fan. Mark the rafter or stud with tape and note the location of the vent damper. You’ll enlarge the opening by making an “L” shaped cut opposite the stud and in the direction of the vent damper. Measure and mark the new cut lines or tape the cutting template (supplied with your new bathroom fan) in place. Then, leave the old housing in place while you make the cuts with your drywall saw. Use care when cutting near the flexible vent to avoid damaging it.


Locate the electrical junction box inside the fan housing. Remove the junction box cover screws or squeeze the cover together until the locking tabs disengage. Then disconnect the house wiring and unscrew the electrical clamp locking ring.

Next, locate the screws or nails that secure the fan housing to the stud or rafter. Remove them by hand or with a reciprocating saw and metal cutting blade. If you have blown-in insulation, slide a piece of thick cardboard into the newly cut opening as you remove the old housing. That’ll prevent the insulation from falling into the bathroom. Later, in Step 9, slide the cardboard sideways as you push the new housing into the mounting frame.


Slide the mounting frame into the enlarged opening. Extend the frame arms out to the rafters or studs on each side of the frame and fasten to them with 1.5-inch construction screws.


Thread the house power wires and electrical clamp into the round hole in the new fan housing and screw the locking ring onto the clamp. Then slide the housing into the mounting frame until it clicks in place.


Connect the flexible duct to the damper assembly and seal the connection securely with aluminum foil HVAC UL-listed tape (not ordinary duct tape). Orient the damper according to the diagram shown on the instruction sheet and attach to the housing using the supplied fasteners.


Connect the hot (black) and neutral (white) wires to the corresponding wires inside the fan housing. Wrap the house bare copper wire clockwise around the green grounding screw in the housing and tighten. Connect the remaining bare copper wire to any green wires using a twist on wire connector. Consult the wiring diagram shown on the fan’s instruction sheet to double check your connections before restoring power. Secure the junction box cover with the screws provided.


Push the fan assembly into the housing and secure with the screws provided. Install the silencer baffle (if provided) using the screws included with the kit. The baffle is an important noise reduction component—don’t leave it off. Plug the fan into the receptacle in the housing. Then, turn on the power and test the fan.


Fill the gap between the fan housing and the drywall with a generous bead of fire caulk to prevent warm air from bleeding into your attic. If the gap is ½-inch or larger, use a fire-rated expanding foam.


Locate the grille spring connector in the housing slots and push the grille into place. Square the grille by sliding it slightly with your fingers.

Test the fan again: The fan should run quietly with no rattling (which would otherwise indicate that you’ve left out a fastener). Now, check its suction power by holding a small piece of toilet paper near the grille. The fan should suck the paper towards the grille. Finally, test for proper damper operation by holding your hand in front of the grille with the fan off—you shouldn’t feel any air movement. If everything checks out, clean up the work area and tell all of your friends how handy you are!

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