How Ceiling Fans Work?

You certainly appreciate it keeping your rooms cool in during the summer heat? But do you know how your ceiling fan works? We take a look inside the breeze machine.

Installing a ceiling fan is easy, according to how-to videos and breezy online tutorials. But these instructions assume that an electrical box rated to hang 70 pounds of fan is just sitting in the ceiling, mounted to a joist on bolts strong enough for chin-ups. Sorry, but unless you’re replacing an existing fan, that box isn’t in place yet.

What is there, most likely, is a basic lighting fixture connected to someone else’s electrical work—a pile of wiry pigtails bearing a strong resemblance to a can of worms. Replacing it involves clearing out a wrist-size hole and then reaching back in to mount a metal box, clamp the wires and secure their connections, all while never once getting a clear look at what you’re doing. Now, many amateurs can hang a pot rack or an overhead planter, and most can wire a receptacle, but few can do both at the same time. If the project gets unmanageable, a licensed electrician can finish the job for around $175.

Once the box is in, the work really is easy, and a lifetime of cool breezes is within reach. 

 

Dust in the Wind

Fan blades attract dander, dust mites and more. Antidust products keep a fan clean, but do they bust the dust better than a wet rag? We polished a filthy old fan and a brand-new one to test four common options.

1 Endust Worked well, but an ingredient list heavy with petroleum seemed like overkill for a dirty fan.

2 Pledge Broke up thick crud with a pleasing lemon scent. Shiny, clean finish.

3 Swiffer Too flimsy for the filthy fan, but its crimped fibers found dust on the new blades.

4 Wet Rag Elbow grease and dish soap did the trick on both fans.

The Bottom Line Chemical cleaners work, but soap is cheap—and safe for skin contact.

3 Sounds of Fan Failure

Squeaking A series of squeaks suggests a loose screw. Tighten fasteners connecting the canopy, the blades and the globe.

Clicking Clicking indicates a bearing gone bad. It happens. The bearing (or motor) may be replaceable. Ask the manufacturer.

Wah-Wah It's over. This magnetic noise signals defective internal motor components, a problem in cheap fans. Replace the fan. 

 Induction motors use a rotating magnetic field to move machinery. Nikola Tesla demonstrated the technology in such devices as 1893’s Egg of Columbus. Early motors operated at a single speed; semiconductors made them more practical by enabling variable-speed operation.

 

1 Wires Conductors carry electrical current to sets of copper coils called windings.

2 Windings Wrapped around steel bars, or laminations, energized windings form an electromagnet called a stator.

3 Stator Fluctuating polarity creates a rotating magnetic field in the stator. The field crosses a 0.3-mm gap to induce a current in laminations in the rotor, which spins around the stationary stator.

4 Rotor The angle at which the stator faces the rotor, the physical distance between the two, and the geometry of slots carved into each set of laminations combine to create two out-of-phase magnetic fields. The rotor spins because it repels the rotating magnetic field induced by the stator.

5 Housing The motor housing envelops the rotor as it revolves on bearings around the stator. In the design shown here, known as an inside-out motor, fan blades attach to the housing bottom. Vents on top cool the motor—it needs a breeze, too.

Blade Geometry

Blade Tilt Most blades tilt between 12 and 14 degrees off horizontal. Decorative blades, such as textured palm fronds, can tilt up to 20 degrees.

Fan RPM Fans on low speed revolve 40 to 70 times per minute. Medium speeds range from 100 to 115, and high speeds hit 180 to 200.

Blade Count A high blade count cannibalizes airflow per blade, according to manufacturer Fanimation's John Moody. "Looking strictly at what moves the air most efficiently, three blades are best," he says.

Rotation Rule Blades tilt so that a counterclockwise rotation pushes air downward to cool a room. Reverse the rotation, and blades draw air upward to circulate the hot air hugging the ceiling without creating a direct draft into the room. Here's the rule: Go clockwise in cold weather.

Ideal Blade Length Per Room Size

 

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