How to Install a New Bath Vent Fan

When building a new bathroom, you can't forget the vent! This important feature is responsible for keeping your bathroom free of moisture, mold, and mildew.

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If you've ever been in a closed bathroom after a long shower, you know how important a bathroom vent can be. The steamy moisture can ruin walls and wood features when left in the air. Bathroom vents also do a good job at keeping our families safe from the harmful fumes often found in bathroom cleaning agents. 

Installing a new vent in a bathroom is a hefty task, but it can be done by homeowners with experience in siding, roofing, and electrical work. Below, we show you how to safely get the job done.

Master Bethroom Remodeling

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Getting Started

Plan the installation so the vent duct is as short as possible and makes as few turns as possible. In addition to a vent fan, a bathroom unit may have a light, night-light, or heater. A heater uses more power than a light and fan, so it may need to be on its own circuit.

A fan or a unit with a light and fan that come on at the same time requires only two-cable wiring. Wiring becomes more complex with separate function controls and additional functions. To replace an existing fan, check the wiring; you may need to replace two-wire cable with three-wire cable or even two cables.

What You Need

  • Voltage tester
  • Pry bar
  • Drill
  • Drywall saw
  • Jigsaw
  • Hammer
  • Ladder
  • Fish tape
  • Screwdriver,
  • Strippers,
  • Long-nose pliers
  • Lineman's pliers
  • Vent fan
  • Switch
  • Ductwork
  • Duct tape
  • Sheet metal screws
  • Cable
  • Clamps
  • Switch box
  • Wire nuts
  • Electrician's tape

How to Install the Vent Fan Housing

Step 1: Remove Existing Light

To replace an existing ceiling light with a fan/light, shut off power to the circuit. Remove the light and pry out the ceiling box. If you cannot work from above, cut carefully around the box before prying. You may need to cut through mounting nails.

Step 2: Mark Opening

Disassemble the new fixture and use the housing as a template to mark for the opening. The fan must be securely mounted; if there is no joist to attach it to, install blocking nailed to nearby joists.

Step 3: Cut Opening

If necessary, install blocking to keep the insulation away from the fan. Cut a hole with a drywall saw or reciprocating saw. If the ceiling is plaster, drill locator holes at the four corners and cut the opening from below.

Step 4: Attach Fan

If necessary run new cable from the switch to the box. (The fan shown has separate controls for fan and light and requires one three-wire cable.) Screw the fan to a framing member.

Step 5: Cut Duct Hole

For the wall vent, drill a locator hole from the inside through the outside wall. Outside, cut a hole for the duct.

Step 6: Attach Duct

Measure from the outside to the fan. Attach a piece of solid duct to the wall cap so it is long enough to reach the fan or as close as possible. Fit the duct to the cap, drill pilot holes, and drive sheet metal screws to hold it in place. Cover the joint with professional-quality duct tape.

Step 7: Attach Cap

Apply a bead of caulk around the exterior hole. Slide the duct through the hole and fasten the cap to the wall with screws.

Step 8: Fill Gaps

Fill any gap between duct and fan with another piece of solid duct or with flexible metal ducting. Clamp each joint and wrap with duct tape.

Bonus: Venting Through Walls and Soffits

If possible run the duct straight out through a wall. Or go up into the attic, over, and out through the soffit. If there is no room above, the best solution may be a special vent fan that you can mount on the wall.

Bonus: Venting Through the Roof

To vent the fan out the roof, cut the hole from inside or drill a locator hole and cut the hole on the roof. Attach a short tailpiece onto the roof jack and install it. From inside, run flexible ducting from the fan to the jack, clamp each end, and cover the joints with duct tape. To prevent condensation from dripping near the fan or on the ceiling below, wrap the entire duct with pipe insulation.

To install a roof jack, follow the manufacturer's instructions exactly to prevent leaks. First cut through the roof, then cut back shingles. Install the jack and cover its top half with shingles. Cover all nails with roofing cement.

How to Wire a Bathroom Vent Fan

Step 1: Run Cables

First, turn power off. If necessary run the correct cable or cables to the switch box. As shown above, power enters the switch box. If power enters the fan, see the manufacturer's instructions.

Step 2: Wire the Switch

To wire a fan/light switch, connect the grounds and splice the white wires. Connect the red and black wires from the fan to the fan and light terminals. Connect the feed wire to the remaining terminal.

Step 3: Wire the Fan

Connect the grounds and splice the white wires. Splice the black wire to the black fan lead and the red wire to the colored lead. Attach the junction box cover. In the bathroom, install the light and the fixture canopy.

Wiring a Multipurpose Unit

The more functions a switch controls, the more complicated the wiring. For instance, to wire a fan/light/night-light with separate controls for each, run two cables—one two-wire and one three-wire—from the switch to the fan.

Consider This: Timer Switch for a Fan with a Heater

Leaving the fan heater on wastes energy and creates a hazardous situation. To avoid this, install a timer switch along with a two-function switch for the fan and light. To do so install a double-gang box.

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