I have a vent fan and an overhead light in my bathroom. They are currently tied to one standard light switch. When that light switch is in the "on" position, the vent fan and light are both powered on.

I want to replace the existing standard switch with a dimmer, but do not have space to add an additional switch in the room for the vent fan. The vent fan needs a full 120V to operate properly. I also want to ensure that the vent fan is running if someone ever has the light on in this bathroom no matter the dimmer setting, so adding a second switch doesn't help solve that problem even if I did have the space.

Is there a dimmer light switch sold that has both the variable voltage output (for the light) and a constant 120V output when the switch is on? I've searched the internet and called Lutron but haven't found anything.

If not, can you think of another way to solve this problem?


2 Answers 2


Check out lutron SFSQ-LF-GR 120v 360w 1.5 amp 3 speed fan control light switch on 1 yoke this will fit in your existing space since that was your concern. I may have mis read your question, so here is a light dimmer with a separate on off switch for the fan, Lutein MA-L3S25-WH. Hope one of those works. Or a pir sensor and switch so the fan turns on when you enter and a light switch combo but those are really expensive.

  • Thanks for the suggestion, Ed. I called Lutron about this device and it is essentially just two independent switches, unfortunately. The toggle switch controls on/off separately than the slider switch, which means a person could still turn the lights on without running the vent fan.
    – Doug Hill
    Feb 18, 2019 at 16:37
  • Use a fan control switch, +1. I prefer infinitly variable if it's going to be used as a dimmer though.
    – Mazura
    Feb 18, 2019 at 16:38
  • Mazura - Do you know of a fan controller where the toggle switch is the master switch to both outputs? The SFSQ-LF is just two independent switched according to Lutron customer service.
    – Doug Hill
    Feb 18, 2019 at 16:39
  • All standard fan control switches do nothing until you flip the switch. Basically you tie them together and when you turn it on, the fan is 'dimmed' but still runs, no matter what. That's how you can dimm a ceiling fan with only one wire.
    – Mazura
    Feb 18, 2019 at 16:41

You can do this by mildly abusing a 3-wire fluorescent dimmer

While incandescent lights are happy with only a dimmed-hot and a neutral, some lighting systems (such as fluorescents) are tougher to dim using standard two-wire dimming. As a result, dimmable fluorescent setups use different ballasts that accept multiple inputs: one switched-hot to provide constant power for filaments and controls, and something else that controls the brightness of the light. The simplest "something else" you can use is a dimmed hot, and as a result, you get what are called "3-wire" dimmers and fluorescent ballasts, using a switched-hot, a dimmed-hot, and a neutral between dimmer and ballast.

In your case, while this isn't an officially sanctioned way of installing such a thing, a 3-wire dimmer is simple as all the switched-hot is is a tap after the internal switch, but before the dimmer electronics. As a result, you can put a 3-wire fluorescent dimmer in (Lutron makes them in most of the styles they make), then use the switched hot to control the vent fan and the dimmed hot to control the lights. Of course, you need to have a 3-wire cable running up to the fixture to do this; furthermore, these dimmers require a neutral, so if it's on a switch loop, you'll need to use /4 cable in order to provide neutral to the dimmer.

  • This sounds just about perfect. I didn't see an obvious part number for a single gang 3 wire florescent dimmer while searching a Lutron's website. I did come across this on Amazon, but it is a 3-way. [AYF-103P](amazon.com/Lutron-AYF-103P-WH-Ariadni-Single-Fluorescent/dp/… Is that similar to what you were talking about?
    – Doug Hill
    Feb 18, 2019 at 17:44
  • @DougHill -- in general, these dimmers will be single-pole/3-way combination configurations, yes Feb 18, 2019 at 19:20
  • @Harper -- actually, the other question is talking about a standard Ariadni dimmer for incandescents... Feb 21, 2019 at 0:42
  • @ThreePhaseEel Yeah, I lost my place on the site and ended up looking at a beast of a breaker intended for pilot-signal (10v?) control of fluorescent ballasts. Had green, white, red (switched hot), blue & purple (line/3-way), and orange (pilot signal) terminals. Feb 21, 2019 at 1:40

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