Dear Mr. Electrician: How do I determine if I need an attic fan replacement?
Answer: You may not need a full attic fan replacement. Many times it is just a matter of replacing the fan thermostat or the attic fan motor or sometimes both. NOTE: Text links below go to applicable products on Amazon and EBay.
A simple test to determine if a full attic fan replacement is needed is to disconnect the thermostat and hard wire the fan motor directly. If the motor works fine like that, a new thermostat is needed. If the motor doesn’t work, or hums, or makes noise, you need a new attic fan motor.
I have repaired and installed a number of attic fans in my career as an electrician. Although the work is pretty straight forward, it becomes challenging given the working conditions. It is rare that a full attic fan replacement is needed.
Replacing the roof mounted attic fan motor involves climbing up in an attic with tools, safety gear, parts, water, and lighting. In some instances I have had to put plywood on top of the ceiling joists and bring a ladder up into the attic to reach the fan motor comfortably enough to work on it.
Sometimes I had to do this twice, once to diagnose the problem with the fan and get the model number, and the second time to actually replace the attic fan motor. Attic fan motors are proprietary and are not interchangeable even though many look alike.
It is important to get the correct model number of the fan before searching for attic fan replacement parts. The model number on the fan motor itself can be helpful in tracking down a replacement, but having the original fan manufacturer’s name and fan model number is the best.
The fan motor above had bad bearings and was making a loud noise when turned on. I disconnected the thermostat and wired the motor directly to test the motor. This fan had an accumulation of dust because the dryer vent duct up to the roof was leaking air and the fan sucked up the dust. The dust inhibits air flow through the motor for cooling purposes. The motor could overheat and fail prematurely.
The fan model above has its thermostat mounted directly on the fan. Other brands have the thermostat a short distance from the fan blades.
HOW I REPLACE AN ATTIC FAN MOTOR
It begins with my work pants that have built-in kneepads and side pouches. I also have a dust mask or a respirator to wear. Sometimes I will wear my hard hat, but it can be inhibiting depending on the working conditions. Work gloves are also important to keep from getting splinters when grabbing onto wood beams. I wear a head light and if there is no other light will bring a drop light and cord up there.
Though it may be summer and hot in the attic, I always wear lightweight long sleeve work shirts. Insulation on the skin is not pleasant. What I do to help cool the attic is open a few windows in the home. With the attic hatch open this allows a natural flow of air upwards through the attic. It does make a noticeable difference when working up there. I also bring my water bottle with me.
As mentioned previously, accessing the attic fan motor can be a challenge. In addition working on the fan requires some tools that not everyone has in their tool box. I had to buy some unique, but not unusual tools to work on attic fans. I already owned 3/8″ and 1/4″ drive ratchet wrenches, but I needed some additional extensions and flexible joints. I also had to buy several different sizes of Allen Wrenches that would attach to my ratchet wrenches.
I put all of the tools that I think I will need into a five gallon bucket to make it easier to carry up into the attic.
If there isn’t a disconnecting switch in the attic, I have to shut power off at the circuit breaker, after I locate the correct one. Then I disconnect the wiring from the fan motor and/or the thermostat.
I loosen the three bolts on the round clamp that holds the motor in place. Depending on the positioning of me in relation to the fan I will use some wrenches or the 3/8″ ratchet.
I used to try to remove the fan blade first so it would be easier to drop the motor, but the fan blade tends to be frozen on the motor shaft. Now I remove the motor with the fan blade attached as it is easier to work on it on the ground. Have some penetrating oil for that. The fan blade is held in place on the motor shaft by an Allen screw. Every fan blade has a different size Allen screw.
Next I will remove two or all three of the bolts and nuts and separate the brackets apart. This allows the fan motor to drop down, but not to the floor because the fan blade gets caught on the brackets. The fan blade has to be wrangled around the brackets without damaging the blade. A bent blade could cause the fan motor to wobble, thereby making noise and shortening the life of the motor bearings.
With the old motor on the ground I will transfer the fan blade to the new motor. I will also do whatever motor wiring that I can while it is down.
Installation is pretty much the reverse of the above with care taken not to bend the fan blade. Once the motor is locked in place I will work backwards to the thermostat and the disconnecting switch to get them as they should be.
Some thermostats have a test button on them to test the motor if the temperature is not hot enough. Most of the time I can just lower the thermostat setting all the way down to activate the motor.
HOW I WIRE AN ATTIC FAN MOTOR
On a routine call to replace some smoke alarms, one of which was in the attic I discovered the above wiring mess on a perfectly good and running attic fan. I showed the homeowners my pictures and they authorized me to make repairs.
Fortunately in this case an attic fan replacement motor was not needed, only a wiring repair. It is important that the 3/8″ flexible metal conduit is screwed on to the nub where the wires exit the fan. This ensures ground continuity. The leads on the motor are usually long enough.
3/8″ flexible metal conduit can usually be purchased at an electrical supply company. Some of them will cut it by the foot.
Attic fan thermostats are much easier to find than motors. Attic fan thermostats are less proprietary and usually interchangeable. The Home Depot stocks an attic fan thermostat that will work on several models of attic fans. They also stock one brand of attic fan replacement motor. Do not buy their fan motor unless you are absolutely sure it is the correct model.
The combination device above served as the shut off switch for the same attic fan with the wiring mess. This was in a condominium attic which also contained the forced air furnace which is why there was a smoke alarm up there. The working conditions were quite cramped.
From the way this fan was wired it was clear to me that it was done by someone without much, if any electrical wiring experience.
The metal switchbox was overloaded with wires and in violation of the National Electrical Code. The cable clamps in the box each count as one wire when determining cubic inch capacity. Each wiring device such as a switch or an outlet counts as two wires. For more information on cubic inch requirements see article 314.16.
Although there were grounding conductors inside the box, none of them was bonded to the metal box. If the insulation on one of the current carrying wires was damaged and came in contact with the metal box, it would energize the box, but not cause the circuit breaker to trip off. All metal must be grounded.
A disconnect switch is required within sight of the attic fan for servicing purposes.
A GFCI electrical receptacle was required in this particular location for the servicing of the attic installed furnace.
ATTIC FAN REPLACEMENT
The above attic fan came up in a home inspection report on a house being sold. The homeowners needed to get it fixed right. I was not able to locate an attic fan replacement motor for this unit. I contacted a motor repair shop to see if they could repair the old motor. The motor shop told me that these motors are proprietary and their parts are not universally compatible. They suggested bringing the old motor to them to see if they could match it up with something.
I spoke with the homeowners about the problem finding the correct attic fan replacement motor. They said to just go ahead and replace the entire fan unit.
I ordered a new attic fan and hired a roofer to install the fan on the roof since he was better equipped to do that. The roof was old and if any damage to the roof shingles occurred I would not be able to make roof repairs.
The electrical box above contained the thermostat for the old fan motor. First time I saw a setup like this.
Above is the new attic fan replacement unit and remote thermostat. I let the thermostat hang below the roof joist so that it could better sense the air temperature. I usually set the thermostat for 120 degrees. From my own experience with attic fans I found that at 120 the fan will run all day, but not all night. Of course this will vary by region.
I also installed a disconnect switch for the new fan. Forgot my label maker that day.
The tools that I normally carry up in the attic for fan servicing consist of my lineman pliers, screwdrivers, adjustable wrench, Allen wrenches, 1/4″ drive socket wrench with extension bars and a universal joint, and 1/4″ drive deep and short 6 point sockets, 3/8″ socket wrench with extensions bars, universal joint, and 3/8″ deep and shallow 6 point sockets. I also have Allen Wrench Sockets for the Socket Wrenches to loosen the set screw on the fan blade.
In my pouches I will have wire connectors and electrical tape and any hardware that I think I might need. I also need to carry up into the attic the new motor, new thermostat, and any electrical materials needed such as wire, cable connectors, and electrical boxes.
My post with light switch wiring diagrams may be useful to you. Just substitute the fan motor for a light fixture. The wiring is the same.