Installing bathroom vent fan

Discussion in 'Shower & Bathtub Forum & Blog' started by John S. Pratt, Nov 18, 2007.

  1. John S. Pratt

    John S. Pratt New Member

    Nov 18, 2007
    I want to install a vent fan in my bathroom about 6" on the wall above the shower head. The fan may be used over bathtubs and showers when installed in a GFCI protected branch curcuit. The back of the fan would be in a closet and the distance the exhaust duct would travel to the outside is about 18". Do you
    see anything wrong with this location?
  2. geniescience

    geniescience Homeowner

    Nov 27, 2005
    humid summers hot, humid winters cold
    better higher up closer to the ceiling. How high is your ceiling?

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  4. John S. Pratt

    John S. Pratt New Member

    Nov 18, 2007
    The house was built in 1926 and the bathroom has never had a vent.
    The ceiling is 7'9" . The top of the shower arm is 6'6". There is just enough room between that and the ceiling for the fan grille to fit. Above the ceiling(above the tub and shower) there is no crawl space just roof. There is a very small crawl space above the entrance to the bathroom but it is too small for me to fit in. That why I want to put the fan on a wall.
  5. geniescience

    geniescience Homeowner

    Nov 27, 2005
    humid summers hot, humid winters cold
    sounds good. it is high enough.

  6. allnewbath

    allnewbath New Member

    Nov 26, 2007
    Many types of bathroom exhaust fans are available, from the simplest fans, to more elaborate models with built in lights, heaters and timer switches. Some models are designed to be mounted on the ceiling, while others are mounted to the walls.

    Wiring at the Switch

    Wiring at the switch should be performed after the unit has been installed. However, since your choice of switching for the installation determines the type of cable that must be run from the switch to the fan unit, the information is included here first.

    Installing a fan/light combination as a replacement for an existing light fixture is an easy project. The wiring is already in place, so the project requires no special knowledge of electrical wiring. For this installation, the light switch will operate both the fan and the light at the same time.

    If you wish to operate the light and fan independently by separate switches, it will be necessary to run a 3-wire cable between the unit and the existing light switch and install a double switch at the electrical box. The switches should be wired as indicated in the drawing.

    Exhaust fans with lights/heaters/and or timers may require additional cable from the existing switch box to the fan. Consult the manufacturer’s instructions. These more sophisticated exhaust fans often include their own timers and switches which are designed to fit the existing switch box.


    1. Shut off the power to the circuit before you begin any work. Lock out the circuit or the panel so no one can turn the circuit on while you are working. From the attic, remove any insulation from above the area of the ceiling in which you plan to mount the fan.If you are replacing a light fixture with the fan unit, remove the existing fixture and disconnect all electrical connections.

    2. If possible, place the housing in a position which will allow you to fasten it directly to a ceiling joist. If this is not possible because of the location of the original light fixture, install a wooden braces between joists to provide a solid attachment point for the fan housing. Hold the housing in place against the ceiling and mark around it to define the perimeter of your cut. Drill pilot holes in the corners, and cut along the lines with a drywall saw or jigsaw.

    Secured fan.
    Secure the fan to joists or braces.

    Secure the fan housing in place.

    4. Run a length of cable from the existing light switch to the exhaust fan unit. If you wish to have separate switches operating the fan and light functions, use 3-wire cable. If your unit includes a heater and/or timer, additional cable may be required. Consult the manufacturer’s instructions. This step is not necessary if you are replacing an existing fixture and do not require independent switch operation for the fan and light.

    5. Make the necessary electrical connections at the fan unit using wire nuts. Follow the wiring diagram provided by the manufacturer. Simple fan installations may only require wiring bare copper to bare copper, white to white and black to black, while more elaborate units with lights and/or fans will require more connections. Attach the ground wire to the grounding clip provided on the housing. Push the wires into the wiring box area of the housing and install the cover.

    6. Connect the duct to the fan housing.

    7. Follow the instructions of the unit’s manufacturer regarding how far away from the fan the insulation should be kept. Some units allow insulation to be right next to the housing. Others, particularly those with lights or heaters, may require that you add dams between the joists to keep the insulation a minimum distance away from the unit.

    8. From inside of the bathroom, install the unit cover.

    9. Wire the cable into the existing electrical circuit at the wall switch.

    Venting the Fan

    This is an important part of fan installation. Improper venting of the fan can cause moisture problems which arise as a result of condensation forming within the vent. This condensation can run back down the duct, leaking around the fan and creating stains and problems in the surrounding building materials. Don’t vent the moisture directly into the attic. After all, your goal is to avoid moisture problems, not transfer them to a different area of the house.
    Vent duct.
    Always vent the fan to your home's exterior.

    When possible, vent the fan through the nearest soffit. This allows you to make the vent installation under the overhang of the roof, preventing the need for a roof vent.

    The fan unit can be connected to the soffit vent using flexible plastic duct material. The duct material is easy to cut and it is expandable, which helps make fitting an easy task. Just clamp one end of the duct to the vent shroud on the fan housing and the other end to the vent. Installing the duct horizontally across the attic reduces the possibility of condensation trickling back down around the fan. Insulating the duct with insulation wrap also reduces the formation of condensation within it.

    Some fans are designed to be installed in the wall instead of the ceiling. These fans are mounted on exterior walls and are ducted directly outside. For these installations, hoods with gravity-hinged dampers are installed against the home’s exterior siding immediately behind the fan. These hoods are similar to the type commonly used for venting clothes dryers.

    I hope all of the information will be helpful.
  7. frenchie

    frenchie Jack of all trades

    Dec 30, 2006
    Brooklyn, NY and Fire Island, NY
    Venting through the soffit is not a good plan - the moist air tends to re-enter the attic through the roof's soffit vents, leads to condensation on the roof deck.
  8. Hube

    Hube New Member

    Sep 1, 2004
    Normally with a proper soffit type grille, an exhaust fan has enough velocity to "throw" the moist exhausted air away far enough so that none of it will ever re- enter back into the soffit/attic area.
    A properly installed soffit grille has many advantages over a "thru the roof"type installation.
    A thru the roof installation has to contend with snow, ice, wind, and also has the chance of rainy day leakage, whereas a soffit vent does not.
    Last edited: Nov 26, 2007
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