How To Install Attic Fan in Roof (*2020 Guide*)

Do you want to learn how to install an attic fan onto your roof?

Attic fans installed on your roof can be a great asset to keep your attic cool during the summer and to prevent ice dams during the winter (here is my review on the best rated roof mounted attic fans).

In this guide, I will go over...

  • The steps required to install a roof mount attic fan
  • An easy trick to locate the exact center for the attic fan
  • How to cut out the roof hole with a reciprocating saw
  • Properly sealing the attic fan with caulking
  • And a simple way to test the thermostat
how to install attic fan in roof

Introduction

Installing an attic fan on a roof is a straightforward process.

There are three basic steps which include cutting the roof hole, fastening the fan, and wiring it to power.

It's also important to make sure that there is enough passive venting in the attic so that the attic fan can work properly. You also want the attic well-sealed from the home interior so it won't pull out conditioned interior air. 

In addition, if you don't have enough attic insulation, it can greatly reduce the effectiveness of an attic fan installation. I recommend that you make there is at least a foot of insulation on the attic floor.

It is estimated that good attic venting can reduce your attic temperature by up to 25 degrees Fahrenheit. 

Read Also: What Are The Best Rated Roof Mounted Attic Fans?

#1. Choose Where To Install The Attic Fan

The first step when installing a roof mounted attic fan is to determine where to place it. In general, you will want to install the attic fan about 2-feet below the ridge of the roof.

Also, it is best to place the fan towards the middle of the roof in the horizontal plane. If you install the attic fan towards one side or gable, then the ventilation will be heavily favored on just one side.

In addition, you want to keep the attic fan away from any passive vents as much as possible.

If you install an attic fan right next to a passive vent, it will suck in air from the passive vent which will interfere with blowing out hot attic air.

Read Also: Venting Your Attic Without Soffits? (Is It Possible?)

#2. Drill A Screw Through The Center

The best trick for proper placement of the attic fan is to locate the spot in the attic.

Mark the exact center between the rafters with a pencil and measuring tape. After you marked the center, drill a screw through the sheathing and through the shingles to the outside so that the screw is poking through the shingles on the outside.

Now its time to go on the roof. Locate the screw that you just drilled poking through the shingles.

#3. Pencil The Attic Fan Outline

Grab the paper template that came with the attic fan.

If an install template didn't come with it, you can make your own by penciling the outline of the fan onto cardboard.

Place the template on to the screw so that it is perfect centered. Now pencil around the template onto the shingles --- so now you have a perfect outline of the attic fan.

Read Also: What Are The Best Rated Gable Attic Fans?

#4. Cut Out The Attic Fan Hole

It's time to drill a starter hole onto the roof for your reciprocating saw. You can use a half-inch wood bore bit to make the hole. Before making any cuts on the roof, wearing eye protection is recommended due to possibly flying wood chips.

Insert the reciprocating saw blade into the starter hole, and cut around the outline that you drew with the pencil.

Make sure not to cut into the attic rafters or trusses because this may cause structural damage to your home.

When you get close to the end of the cut, make sure you grab the screw so that the cut out doesn't fall into the attic. If you don't hold onto the cut out, it may damage your ceiling drywall.

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#5. Prep For Dry Fitting

Before you dry fit the attic fan, just a flat tool such as a pry bar to open up the shingles around the hole where the attic fan flashing will go into.

If there are nails blocking the attic fan flashing, now is the time to cut them.

You can use the reciprocating saw to cut underneath the shingles to cut any nails in the way.

Read Also: What Are The Pros And Cons of Attic Vent Fans?

#5. Dry Fit The Attic Fan

Once you have lifted up the shingles, and cut any nails that will prevent installation, it is time to dry fit the attic fan.

Simply insert the attic fan over the hole, and lift up the shingles over the flashing. The bottom flashing of the attic fan should go on top of the shingles, not under.

How Do You Inspect Attic Fans?

#1. Will It Turn On?

Locate the thermostat (small metal box) usually mounted on a rafter or truss next to the fan in the attic. Turn the temperature knob so it is below the current attic temperature. You can also use a heat gun, hair dryer, or lamp to heat up the thermostat if the attic is cold.


#2. Turn The Blades

If the attic fan doesn't turn on, try turning the fan blades. If the blades won't turn, you may have a seized motor.


#3. Operation Quality

If the the attic fan turns on, are their any weird noises? Does it run smoothly? Can you feel air flow or is it very weak? The fan screen or louvers should not be blocked with debris impeding air flow.


#4. Water Stains

A common problem with attic fans are leaks. Are there any signs of water leaks around the fan on the roof sheathing?

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#6. Fasten The Attic Fan To Roof

Once you are satisfied with the fit, it's time to fasten the attic fan to the roof. Beforehand, it is a good idea to apply a bead of exterior caulking to the underside of the attic fan.

You may also want to fasten the thermostat or junction box to the rafter first if you have poor access in the attic.

Once you have placed the attic fan in its proper position, it is time to install a few screws or roofing nails onto the attic fan flashing.

Read Also: What Are The Best Solar Powered Attic Fans?

#7. Apply Exterior Caulking Or Roof Sealant

After it has been fastened, apply some exterior caulking to the top of the nail or screw heads as well as underneath the adjacent shingles.

You don't want to apply caulking underneath the bottom flashing because you will want water to escape.

#8. Plug In Or Wire The Attic Fan

For wiring the attic fan, consult the wiring diagram for the fan, but in general you will want to connect the black to black, white to white, and the ground wire to the green screw.

If it is a plug in type, then you just plug it in to an outlet inside the attic.

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#9. Secure & Test Thermostat

If you haven't secured the thermostat to a rafter or truss, you will want to do this as well.

Make sure that the air opening of the thermostat is not obstructed, a small hole in the back.

You can adjust the temperature setting on the thermostat which is the temperature that you want to the attic fan to turn on. To test the attic fan, you can simply hold a lamp to the thermostat so that it will warm up and turn on the fan. Please don't use a lighter or flame to test the thermostat.

Read Also: Can Attic Fans Protect & Prolong Your Roof?

Conclusion 

Attic fans can be a great way to lower the temperature of your attic, and possibly prolong the life of your roof covering.

With attic fan installations, the biggest concern is likely to be a leaking roof. To avoid this, it is best to buy an attic fan with extra wide flashing --- you want the metal flashing to protrude along the fan as wide as possible. 

In addition, you want to apply caulking over any screw or nail heads, as well as under the shingles atop and adjacent to the fan. This will help prevent any sideways wind-driven rain from going into the attic fan hole.

Always avoid placing caulking underneath the bottom flashing portion though because you don't want to prevent water drainage.

This is similar to exterior siding. Siding is never sealed or caulked at the bottom so that it will drain any moisture or water that gets underneath.

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company (read his full bio on the About page). To ask Arie a question, please use the comment box at the bottom of the relevant article.

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Home Inspector Secrets is an online resource for owners, buyers, and sellers to understand all aspects of home maintenance. We have detailed home guides, product reviews, inspection advice, and much more.