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In searching this SE, I see many questions discussing traditional ceiling fans and dimmer switches.

This question revolves around bathroom in-wall exhaust fans and dimmer switches. Is it safe to replace a standard on/off switch with a dimmer switch for an in-wall bathroom exhaust fan? Will doing so quickly destroy the fan?

The fan is a standard construction-grade inexpensive in-wall exhaust fan.

The idea is to conserve energy and reduce fan noise.

After my mother-in-law cooks a meal, it can be turned up to full power in order to handle the increased noxious vapors in the bathroom due to all the urgent visits. Otherwise, it can be used at lower levels.

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  • Don't assume dimming saves power, most dimmers themselves waste as much power as they save at the fixture. Ever felt a warm dimmer? That is consumed electricity. – Tyson Nov 21 '16 at 15:30
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    @Tyson no, even though the dimmer gets warm, it does save quite a bit of power (trust me, it would be WAY HOTTER if it was dissipating all the power that didn't go to the lamp -- a typical dimmer is rated for 600W of lighting, and there is no way it could dissipate 600W of heat into a wallbox without burning out the attached wiring!) – ThreePhaseEel May 24 '20 at 23:39
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This kind of fans usually use a shaded-pole motor. From wikipedia:

they are compatible with TRIAC-based variable-speed controls, which often are used with fans

So it appears the fan should be fine.

But there is some risk to the dimmer due to voltage spikes generated by the inductive load. You could try to find a dimmer switch that is rated to control inductive loads, or you could just try it out. A typical fan is pretty low powered device and a typical dimmer might be able to handle the small inductive spikes it will produce.

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  • Thanks. It sounds like your answer is referring to ceiling fan dimmers. Can you expand your answer to include the more common non-incremental dimmers (often used for lights)? – RockPaperLz- Mask it or Casket Nov 21 '16 at 20:42
  • @RockPaperLizard Hmm, I think I do not know enough about the differences to expand it. I have seen both non-incremental (potentiometer) and incremental (buttons) dimmers being used for fans. As far as I know, the only difference is the user interface, and they both use the traditional TRIAC circuit for actual dimming. – jpa Nov 22 '16 at 5:46
  • Thanks. Maybe someone who knows will chime in (obviously I don't know either!). I didn't realize the only difference is the UI - I thought there was a fundamental difference in those two different types of dimmers. But I'm not educated (or experienced) on this topic. – RockPaperLz- Mask it or Casket Nov 22 '16 at 5:56
  • I was always told that common lighting dimmers should not be used for motor control, that only a controller designed for motors should be used. Old variable resistance dimmers cause voltage drop = not good for motors, and get real hot; triac dimmers shut off/on real quick, also not good for motors. I'm not an electrical engineer, just sharing ignorance probably : ) – Jimmy Fix-it Nov 22 '16 at 7:12
  • @JimmyFix-it Huh, do they still use variable resistance dimmers somewhere? :) But all this depends a lot on the motor type, for example synchronous motors do not work with dimmers. So hard to give a general answer, though I think most fan motors are shaded-pole. – jpa Nov 22 '16 at 8:26
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I ran an open motor, shaded pole thru a click-on rotary dimmer.

Controlling the fan speed down to very slow to move warm air across the top of an oil-type portable heater. Never had any issues at min or max RPMs; no warm or hot dimmer, nor motor.

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    Welcome and thank you! When you write "open motor", do you mean a motor without an enclosure, or something else? – RockPaperLz- Mask it or Casket May 24 '20 at 21:51

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