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Repair & Maintenance

DIY Bathroom Fan Installation: Keep the Moisture Out by Putting a Bathroom Fan In

You might be surprised to learn that installing or replacing a bathroom exhaust fan is a moderately easy DIY project. All you need are the right tools and basic electrical and carpentry skills. Follow the steps below for brand-new installation or replacing an existing exhaust fan.
install exhaust ffan

Bathroom exhaust fans are important for removing moisture and bad odors, and preventing the growth of mold and mildew in your bathrooms. It can also prevent wallpaper and paint from blistering and peeling and doors and windows from becoming warped. Grab your tools because we've compiled a step-by-step guide for you to get the job done. 

Prepare for installing your bathroom exhaust fan

1. Do you know the CFM rating for your bathroom? Get ready for some math. You can make sure you buy the appropriate strength fan by calculating the CFM (Cubic Feet per Minute. Multiply the room's cubic footage (length x width x height) and divide by 7.5.

2. How quiet (or loud) do you want your fan? You can usually find a sound rating on newer fans that ranges between 0.5 (very quiet) and 6 (very loud) ones.

3. Where do you want to put the fan? The placement can impact the ventilation. The best spot is at the center point between your shower and toilet.

  • If you are installing a new bathroom exhaust fan: be sure to scope the space out above in your attic. This is where the bulk of the fan will be located. It should be between two joists in an unobstructed area.
  • If you are replacing a bathroom exhaust fan: it’s easiest to put the new one in the same location.

Make sure you have all the right DIY tools and materials assembled.

You’ll want to check this list before you begin:

Tools: Power drill, screwdriver, combination pliers, jigsaw (or reciprocating or drywall saw), foil duct tape, framing square, pencil screwdriver, combination pliers, jigsaw (or reciprocating or drywall saw), foil duct tape, framing square, pencil. If you're running the duct pipe out through the roof, you will also need roofing cement, shingles and roofing nails.

Materials: A vent cap, flexible duct pipe, caulk, screws and wire nuts.You may also need a stepladder, safety goggles, a respirator, roof brackets and roof cleats or a safety harness.

Installing a bathroom exhaust fan:

1. Drill a reference hole and mark the ceiling.

  • With your power drill and an extra-long, 34 inch (1.9 cm) spade bit, drill a reference hole in the ceiling where you will be placing the fan.
  • Measure the vent fan housing.
  • In your attic find the reference hole and clear away any insulation surrounding it. Use the measurements for the fan housing to make sure the fan will fit.
  • Return to the bathroom and measure the fan's intake port.
  • Use a framing square and pencil to mark the outline of the fan's intake port on the ceiling with the measurements.

2. Cut the in take-port hole.

Use your jigsaw to cut out the space you marked. Remember to wear safety goggles and a respirator!

3. Put the exhaust fan in position.

  • Before placing the fan in the hole, attach a 90-degree duct elbow to the appropriate outlet port using foil duct tape.
  • Insert a cable connector through the knockout hole on the side of the fan's housing, then slide the supporting metal brackets into place.
  • Center the fan over the ceiling hole and lower it into position.

4. Secure the fan to the joists.

  • After the fan is positioned correctly, extend each of the metal brackets until they reach the joists on either side of the housing unit. Use drywall screws to secure them.
  • Take the length of flexible duct pipe and attach one end to the 90-degree duct elbow protruding from the fan housing using foil duct tape.
  • Run an existing or new electrical cable through the connector on the fan housing (if your new fan includes a light, you’ll need a three-wire cable), and secure it by tightening the screw on the connector. 

5. Find an exit point for the duct pipe. It should be the shortest, straightest route from the fan housing to the outside, either through the sidewall or roof. Make sure the duct pipe is as straight as possible and that it won't be stretched too tightly.

6. Attach the vent cap.

  • If your exit point is on the sidewall, pick a point between two wall studs and take some reference measurements on the inside so you can locate the same point on the outside. Use a 4-inch hole saw to cut through the wall from the outside, then secure the vent cap in place.
  • If your exit point is on the roof, draw an appropriate sized circle on the inside and use a reciprocating saw to cut it out. Then get on the roof and remove the shingles covering the newly cut hole. Install the vent cap with roofing cement and roofing nails, then replace any loose shingles.
  • Go back into the attic and attach the end of the duct pipe to the vent cap's connector duct using foil duct tape.

7. Wire the connections in the housing unit.

Depending on the type of fan, you may need to wire the connections from the attic or from the bathroom. Read the manufacturer's instructions and check that the power is off before you start.

  • Open up the housing unit and pull out the fan wires from the electrical splice unit. Strip 58 inch (1.6 cm) back from each of the wires on both the fan cable and the electrical cable you inserted earlier.
  • Twist the same color wires together and add the connectors. Wrap the bare copper wire around the green grounding clip or screw and tighten to secure.
  • Place the wires back in the electrical splice unit and reattach the cover.

8. Attach the grille. Plug the blower motor into the electrical receptacle and secure it with the screws provided. Attach the grille by slipping its mounting wires into the available slots in the housing unit. Make sure it's snug against the ceiling. Turn the power back on and make sure the fan is working.

Replacing an existing bathroom exhaust fan:

1. Turn the electrical power OFF at the circuit breaker.

2. Get under the grille to unplug and disconnect.

  • There is probably a lot of debris in there, so put on gloves, safety goggles and a respirator. Remove the grille covering from the old fan.
  • Unscrew or unplug the motor blower assembly from the housing unit, then open up the electrical splice unit and carefully pull out the wires.
  • Remove the connectors and untwist the wires to disconnect them. (Make sure electricity is off first.)
  • Loosen the cable clamp to free the electrical cable from the fan housing.

3. Detach the housing unit in the attic.

  • In the attic, detach the duct pipe from both the vent cap connector duct and the housing unit.
  •  Pull the electrical cable and wiring free from the housing unit.
  •  Using your power drill, remove the screws holding the old fan's brackets to the joists. Lift the old fan through the ceiling.

4. Install your new fan. If your new fan is the same size as your old one, you can install it right away. If it’s bigger, you’ll have to cut a larger hole with a drywall saw. If it’s smaller, you can caulk around the edges of the housing unit to fill in the gaps once the fan is installed.

  • Go to the attic and lower the new fan into the hole.
  • Slide out the extendable mounting brackets and secure them to the joists using your power drill and 1 inch (2.5 cm) drywall screws. You may want someone to hold the fan in place from below.

5. Connect the duct. Once the fan is in place, attach a 90-degree duct elbow to the fan's exhaust port using sheet metal screws. Then attach a new 4- to 6-inch (10.2 to 15.2 cm) duct pipe to the duct elbow.

6. Connect and secure the wiring.

  • Insert the electrical cable through the new fans connector and secure it with a cable clamp.
  • Open up the electrical splice box (from either the attic or the bathroom, depending on the model) and pull out the fan wires.
  • Attach the electrical wires to the fan wires by twisting same color wires together and attaching a wire connector.
  • Wrap the bare copper wire under the ground clip or screw and tighten to secure.
  • Tuck all of the wires back into the electrical splice box and replace the cover.

7. Plug in and re-attach the grille. Go back to the bathroom and install the motor blower assembly by plugging it into the receptacle and screwing to secure. Attach the grille. Test out your new fan by turning the power back on.

Sources: 
http://www.wikihow.com/Install-a-Bathroom-Fan
http://www.thisoldhouse.com/toh/how-to/intro/0,,689843,00.html


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