A DC motor is quieter, uses roughly two thirds less electricity, and turns slowly without complaining. An AC motor is cheaper to build. On a fixture that runs for hours at a time, in a room where people sleep, the difference is not academic.
The mechanical difference, briefly
An AC motor is wired directly to your household current and its speed is set by how that current is restricted. That is why older fans have three speeds and no more: each one is a physical tap on a capacitor.
A DC motor runs on direct current, converted by a small transformer inside the housing, and its speed is set electronically. That is why DC fans typically offer six speeds rather than three, and why the lowest one can be genuinely low.
Noise is the difference you notice
An AC motor hums because alternating current makes its windings vibrate sixty times a second. Good build quality lowers that hum. It does not remove it, because it is inherent to how the motor works.
A DC motor has no such hum. What you hear instead is the sound of air over the blades, which rises with speed and is close to inaudible at the lowest setting.
Energy use over a season
A typical AC ceiling fan draws somewhere around 75 to 100 watts. A comparable DC fan draws about 35. Run either one for eight hours a night through a long summer and the gap becomes visible on a utility bill, though it will never be dramatic: a ceiling fan is a small load either way.
The more useful way to think about it is that the DC fan lets you leave it running at low speed without thinking about it.
The low speed is the real argument
Three speeds sounds like enough until you try to use a fan in a bedroom. On many AC fans, the lowest setting is still too much air and too much noise to sleep under, so people switch the fan off and open a window instead.
Six speeds, with a genuinely gentle first setting, changes what the fan is for. It also makes the reverse direction usable in cold weather, where the point is to turn the air over slowly rather than create a draft. We covered that in which way a ceiling fan should turn.
What you give up
Two things, honestly.
A DC fan costs more, because the electronics cost more than a capacitor. And a DC motor depends on a control board, which is one more part that can fail, whereas an AC motor is about as simple as an electrical device gets. In practice both outlast the room's decor, but it is a fair point.
DC fans also require their remote or wall control, since the speed is set electronically. You cannot run one from a plain wall switch alone.
Common questions
Can I put a DC fan on a dimmer switch?
No, and you should not try. A dimmer restricts current, which is exactly what a DC motor's electronics are there to manage. Use the supplied remote or a compatible wall control.
Does a DC fan move less air?
No. Airflow comes from blade span, blade pitch and speed, not from the type of motor. A DC fan of the same size moves comparable air, more quietly.
Is the transformer noisy?
It should be silent. If you hear a whine from the housing rather than the blades, that is a fault worth reporting rather than a characteristic of the technology.
What if the remote is lost?
Replacements are available, and most DC fans also accept a hardwired wall control, which is the better answer if you lose things. All of ours do.
Where this leaves you
If the fan goes in a garage or a workshop, an AC motor is perfectly sensible. If it goes in a bedroom, a nursery or a living room where people talk, the quiet setting is worth the difference.
Every fan we make uses a reversible DC motor with six speeds. You can see the range here.