I hired an electrician to install my Broan CST80SLW vent fan with light/fan/humidity detector. When he got the old unit out (fan/light wired to two separate switches) he said the new unit could not be wired to the two separate switches but that I had to buy a special double switch (and could not use the triple switch for full function bc my house wiring didn’t have enough wires in it??). He also said I couldn’t use one of my existing switches and a new double switch to have all functions. Somehow this just seems like he was in a hurry and didn’t want to make things work. In the end I have a light but no fan (or I would have been stuck with a big hole in my ceiling.) Now I have to go buy a double switch, have a switch on the wall that doesn’t do anything, And wait 2 weeks for him to come back and finish. Do I need to hire another electrician??

Wiring diagrams from manual: enter image description here enter image description here

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    confused here. What is the triple switch supposed to operate? Light, fan, and what else? If the old fan/light was working on separate switches, I cannot understand why the new one will not.
    – RMDman
    Commented Oct 28, 2022 at 21:30
  • Re: "could not use the triple switch for full function bc my house wiring didn’t have enough wires in it??)" He may just mean here that the existing wires from the 2 switches to the fan/light do not have enough wires to support the extra humidity detection function. It might be very expensive to run additional wires from the switch area to the vent fan area.
    – Armand
    Commented Oct 28, 2022 at 22:52
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    Can you post photos of the existing switches?
    – Armand
    Commented Oct 28, 2022 at 22:54
  • 1
    What functionality do you want from your fan? Commented Oct 29, 2022 at 1:58
  • 1
    How big (how many gangs) is your switch box?
    – jay613
    Commented Nov 8, 2022 at 10:49

5 Answers 5


Your electrician is most likely wrong. It sounds like your original setup was like this:

  1. Power comes into your switch box and connects to two separate switches (one for the light and one for the fan)
  2. There are probably 3 wires (not including the ground wire) running from the switch box to the old unit (probably a black, red and white wire).
  3. The white would be the neutral, and the other two are the hots for the light and fan. If this is the case, you will need to wire the new unit up as shown in option #1. (You would need 1 more hot wire to use option #2).

For option #1 you do NOT need a special double switch. You can simply use the 2 switches you have (the "special double switch" just fits 2 switches into a single space). Either way, this is how the unit will work.

Fan Switch:

  • Off- Auto humidity control is off
  • On- Auto humidity control is on

If you want to manually turn the fan on - switch must already be on, then flip the switch off then quickly back on (unless you turn it off, it will run for the set time).

Light Switch: (no jumper between black and grey)

  • Off- light is off
  • On- light is on

Light Switch: (jumper between black and grey)

  • Off- light & fan are off
  • On- Light and fan are on

Regardless if you use the jumper or not, the light switch has no effect on the fan switch.


To answer this question in case anyone is curious: The electrician was wrong. I have the Same Setup as OP where I have a switch for the fan, and a switch for the light in my bathroom setup. There are technically 3 sets of wires: One set for the light, one set for the fan and humidity sensor, and one for the optional always on function of the fan (which is a grey wire).

I think the problem with Braun's instructions is that it's overly complicated and they make it seem like you have to buy their double switch (https://www.amazon.com/Broan-NuTone-P2RW-Two-Rocker-Control-Bathroom/dp/B0886KMV8T/ref=asc_df_B0886KMV8T/?tag=hyprod-20&linkCode=df0&hvadid=459579282194&hvpos=&hvnetw=g&hvrand=8796256200313532447&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9053616&hvtargid=pla-951034361431&psc=1) which isn't the case.

The wiring that went to my fan from the two separate switches comes out of a single 14-3 wire with a ground, white (neutral), black (hot) and red (hot).

All white wires from the vent box would be wired together, as did the green to the ground. Then it was black to the brown, then red to the black.

If you were to wire the grey wire to the light, then the fan will always be on once you turn the light on, hence that optional function.


Option 1 in the following YouTube video by Broan. It’s the same wiring function as this CST80SLW or CST80SL unit: https://youtu.be/KlLB2u_NVCc

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    Can you describe the process please, lest this post become useless if the YouTube link dies? Commented Dec 14, 2022 at 4:47
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    – Community Bot
    Commented Dec 14, 2022 at 9:05

I plugged in both the light and the fan to 110v receptacle one at a time. And they both came on when plugged in. So to use the switches for light and fan on my wall, I cut plugs off and wired fan to fan switch and light to light switch. Now unit is fully functional with separate switches for light and vent fan. (connect ground to housing ground)

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    How does this answer the question? Commented Feb 17 at 10:51

You can get info here: Broan Acording to Broan you need to purchase the switches designed to allow all functions. The switches should be available where the fans are sold.

  • 1
    This doesn't really address the OP question about whether the electrician is correct about being unable to use the existing switches. It seems wiring option #1 can be adapted to use existing single light and fan switches.
    – Armand
    Commented Nov 8, 2022 at 7:04

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