Installing a Bathroom Fan and Vent
Credit: mjpyro

If you already have a bathroom fan in your bathroom, or just recently installed one, it is important to vent it properly to remove moisture from the room. Typically this can be done one of two ways. If the bathroom is close to an exterior wall, it can be vented out the side of the wall. However, this is not always possible and most prefer to vent it out a stack in the roof to keep any moist or exhaust from coming out near ground level. Some people prefer not to have that steamy look coming from the side of their home, so placing the exit on the back of the roof, near the ridge line as high as possible, presents the best option for most.

Venting a bathroom will improve the atmosphere in your bathroom because it pulls that moisture and humidity out of the air so that the area is not prone to mildew or rot. It is particularly important to have the bathroom fan working while you take a shower or bath, and leave the fan on for 15 minutes after you finish to suck most of that humidity up and out of the house. In fact, most municipalities require that bathrooms be vented properly.

However, your results will depend heavily on the type of fan you select. The cheaper models do not really do anything except make a lot of noise, so this is not the time to cheap out. Expect to pay around $100 for a really quiet model with a built in light.

If you do not already have a fan installed and are thinking of buying one, here are some pointers on the types you will see at the home improvement store.

Fan Options

Cheap and Noisy – If you are going to buy a $20 or $30 fan, expect it to do little more than make a lot of noise. The motor in these types of fans usually are not strong enough to create the suction action that is required to pull air within the chamber and pass it through to your venting.  Be sure to measure the dimensions of your room, then take that with you to big orange or big blue and look on the product descriptions. Most will give you a recommended range of coverage. Some displays may even be connected so you can get a demo of how they sounds. A good test of how much suction a model has is to hold a small piece of towel paper up and see if it grabs it and holds it against the grill. If it cannot hold up that, it is not going to be worth the trouble of buying it and installing it.

Light – Some units come with only a fan, so if you that is your only outlet for a light, you will need to look for a model with a light built-in.

Automatic Activation – Check your local building codes becomes some areas require that whenever the overhead light is turned on, the fan also activates. However, I can tell you that this can be annoying, so I prefer separate switches.

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Before You Begin

You will need the following supplies and tools before you start to vent your bathroom fan. For the purpose of this discussion, we will assume you are going through the attic into the roof.

  • Power Drill
  • Keyhole or reciprocating saw
  • Hammer
  • Screwdriver
  • Bathroom flexible fan vent
  • Roof cap
  • Roofing cement
  • Caulk
  • Wire nuts
  • Duct and Electrician’s tape

Buy a flexible vent that is long enough to reach the roofline with some a little slack built-in. Choose a short direct path even if it is low on the roof line. Wall vents are easier to install, so if you have that option, you may want to go that route, however, since the roof vent is more difficult, we will focus on that process.

Installing a Bathroom Fan and Vent

The following installation assumes you have access to your attic. If not, you will have to cut from the bottom using a stud finder to locate the nearest ceiling joist.

  1. Go into your attic and lay the fan down and draw a line around it square. This will be the outline you use to cut a hole (if none already exists from the old fan) in the ceiling drywall. Locate the fan near the shower or tub, but not necessarily directly over it. Locate it as central to the room as possible near a ceiling joist which will be used to support the fan box.
  2. Shut off the power to the bathroom at the circuit breaker box.
  3. Attach the fan to the closest joist with screws provided. Be careful not to encapsulate the fan with insulation as some models require a certain amount of space between the unit and insulation. If necessary, push the insulation back about 6 inches. If it is blown-in insulation, you may have to make a little dam with another piece of wood to keep the insulation away from the box.
  4. While in the attic, cut a hole in the roof directly above the fan if possible using a reciprocating saw. To get the hole started, you will need to use a power drill with a boring bit or something similar just to make a hole large enough to stick the reciprocating blade though. Start by tracing a circle large enough to fit the bottom of your roof cap through.
  5. Now go up on your roof taking the proper precautions of course.
  6. You will be able to see the hole you cut and down into the attic. Cut the shingles around the hole. The lower part of the roof cap will actually rest on top of the shingles. The top part of the roof cap will slide under the shingles above it.
  7. Place the roof cap in place, then using some kind of stiff putty tool, smear roofing tar on the underside of the cap flanges as you insert the cap into the hole in the roof.
  8. Make sure the shingle on the side and above the cap are places over the cap flanges with roofing tar underneath them.
  9. Now nail the flange to the roof with roofing nails, then cover the nail heads with roofing tar.
  10. Go back inside the attic and attached the flexible vent over the hole in the fan assembly. There should be some kind of clamp to hold it in place. Then wrap that connection with duct tape.
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Wiring the Fan

Some people are nervous about working with electricity, but the connections in this project are simple. For the purposes of this discussion, I am assuming you already have wires run from the breaker box since you probably already had an existing fan, or a light fixture at the very least.

If you have a fan/light combo, you will need a three-wire cable from the switch to the fan. If you are unsure about that, you might need to hire an electrician to do the rest of this project. However, if it is just a fan, it should present no issues.

Each manufacture will provide wiring instructions with the fan.

  1. While in the attic, wire the fan by following the instructions, typically black on black, white on white, and some kind of ground wire.
  2. Use wire nuts and wrap the connection with electrician’s tape.
  3. Go back down to the bathroom and wire the switch by removing the plate and pulling out the existing switch from the wall. You will need some space and slack to work with.
  4. For a fan/light switch that has power from the breaker box, splice the white wires together with a wire nut and connect the ground wires together.
  5. Connect power to both switch (we are assuming a separate switch for both the light and the fan) through what is called a pigtail spliced connection.
  6. Now connect the red wire to one switch terminal and the black wire to the other switch terminal.
  7. Go to the breaker box and flip the switch.
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Installing a Bathroom Fan and Vent
Credit: mjpyro

The type of results you get will depend heavily on the type of fan you purchase. This is no timeto be miserly because the roar of a cheap fan doing nothing will wear thin on your nerves.

Always check with local codes before doing any major or minor renovations on your home. They are there to help you, not just take your money. If you are at all weary of working with electricity, you can still do 90% of the install on your own, then hire an electrician to finish the wiring. They still work by the hour so given that it will take them about 10 minutes to wire the whole thing, you should get out for a $100 or so depending on where you live.