I'm looking for a switch to mount in an upstairs hallway that will control an attic/roof ventilation fan. The switch will select whether I want the attic thermostat to control the fan, vs manual-on, vs off (fan will not come on). The price for something like this (center-off, constant-contact (not momentary), single-pole double-throw aka "3-way") whether toggle-style or flat (Decora or similar) is upwards of $50 - $70. Or I can get a plate-mounted SPDT center-off paddle-style switch (something you'd expect to see in an airplane cockpit) for under $10.

I could swear I've seen these 3-way center-off switches in the past. Why so rare and expensive now?

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    A little searching and I found some < $40. But not < $10. I suspect it is simply supply & demand. The combination you're looking for just isn't needed all that much. Most of the time it is either simple 3-way (i.e., no "center off") or use 2 switches (one for total on/off, one for A vs. B). In the case of a thermostat, a typical HVAC thermostat (as opposed to a really simple attic fan thermostat) will include all those functions (all off vs. fan always on vs. fan temperature controlled w/AC or heat). So they don't mass produce them to the same degree and can (and do) charge more. – manassehkatz-Moving 2 Codidact May 20 '19 at 3:25
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    Or use two SPST switches for 2 dollars. – Harper - Reinstate Monica May 20 '19 at 4:09
  • Is this circuitry 24V thermostat voltage, or 120/240 mains voltage? – Harper - Reinstate Monica May 20 '19 at 7:00
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    I did not think it was shopping the OP found them and was asking why they were rare and so expensive that @manassehkatz answered in comment form+ – Ed Beal May 21 '19 at 13:55

Simply lay two common switches right next to each other. One is SPST and turns the whole caboodle on and off. The other is a plain 3-way which selects between "always" or "thermostatic" - common goes to the switched-hot off the SPST, one traveler goes straight to the fan, and the other traveler feeds the thermostat.

You'll need /3 cable between the switches and thermostat, or between switches and fan if the thermostat is on a spur.

If you only have a 1-gang space, you can get dual 3-way switches -- you bridge both commons to each other. On the top switch, one of the "on/off" travelers is disused and the other goes to supply.

The other option is to do the thermostat wiring in 24V low voltage, then you can use any switch you please.

Of course, if your AHJ (local inspector) approves switching mains power with an electronics-tier switch which lacks a UL listing or has a ЯU electronic component listing, then you can use it. NEC 110.2.

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    You could also have one switch for on off, and a three-way switch selecting whether it is auto or manual. – SomeoneSomewhereSupportsMonica May 21 '19 at 3:46
  • Got to say a hack when there is a totally code compliant and approved method already answered. As I said I change - with no reason but this is a Hack in my opinion as backwards ru is a UL approved device and I have passed even TUV 3rd party inspections for international inspection and local residential inspections in 2 or 3 states with the AHJ questioning my use of the switches as 3phase did but Have never failed a inspection with these UL recognized switches, how many can say that? – Ed Beal May 22 '19 at 1:13
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    @EdBeal I don't believe I'm involved at all in your debate with TPE over the validity of the RU mark. However given your concern I'll amend my answer to increase the switch budget by $1. – Harper - Reinstate Monica May 22 '19 at 1:22

I would use a bat handle or a rocker that has 3 positions, these are what you want in the 10$ range, power to the common lug then in the top position it could be on , middle off, bottom thermostat, I’ve done things like this using a blank cover and drilling a hole for bat style switch, and use a dremel tool with cutoff disks to make the square hole for a rocker style switch. Just make sure the switch you purchase is rated for the load and you will be fine.

Added. Since there was a question thrown out about listing I did a simple web search for single pole double throw , 3 position switches. 2vlu3 came up and is U.L. Listed 20amp 125v 2 horsepower 11$, 2gm91-78 15a 3/4 horse power rated 125v also came up 6$ and is listed, both are on-off-on this is what op asked for if the switch “state” has a (on)-off-on the brackets ( ) signify momentary some of the switches you could see the listing stamps but the descriptions had them listed also, both of these just happen to be on the granger site so they are out there, and they are listed if purchased through quality companies (not overseas junk). digit key may be less expensive I saw they had the same model and brand but there descriptions were not complete. There are dozens of them out there some may be double pole double throw no big deal you just don’t use 1 side, most vent fans are fractional horse power and these both are horsepower rated. Code states if not horsepower rated or general use switches the required rating is 2x the FLA (full load amperage) of the motor for switches NEC 430.109.C.1. I saw some as cheap as ~4.50 but already had 2 examples that were listed. A little search probably took less time than questions about listing but I do this all the time.

  • The issue with this is with the listing of such a switch (or lack thereof) – ThreePhaseEel May 21 '19 at 2:59
  • The ones I use are listed granger, Newark, digikey all carry them. Most range hoods use bat handles or the ones I have repaired have they are easier to clean and don’t collect grease as bad as standard light switches. – Ed Beal May 21 '19 at 13:10
  • If you could get me a part number or link for such a switch, I'd love to see it :) that would be really cool to find – ThreePhaseEel May 21 '19 at 22:45
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    The local AHJ gets the last word on the subject. NEC 110.2. That's how Ed can get away with it, but Ed's experience is not applicable to the whole country. – Harper - Reinstate Monica May 22 '19 at 1:30
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    @Harper -- yeah, the AHJ can make that call if they so choose since there's no explicit listing requirement in Art. 404, but I have heard of AHJs or inspectors flagging folks for that (as well as them not flagging), and in the context of this site, I don't consider it wise to rely upon AHJ lenience (since that gives more fuel to the "DIY-is-a-dangerous-hack" voices out there) – ThreePhaseEel May 22 '19 at 2:08

Use a Functional Devices SIB02S

As it turns out, the need for an enclosed, UL listed, SPDT, maintained, center-off switch rated for branch-circuit and pilot duty isn't all that rare, and Functional Devices actually makes such a product, complete with industrial-style Hand-Off-Auto labeling: the SIB02S. While the form factor is a bit odd (it's a switch in a plastic box with a nipple on it, so mounting it may require a bit of help from some conduit parts), it is available through a variety of vendors for a good price (around $10 at the time of this writing), and is rated for 20A @ 120V resistive, or a 1HP motor load @ 120V, so it should be adequate to switch your vent fan.


The SIB02S is not aesthetically appropriate for this location.

The Leviton 5685 or 5686 (not sure what is difference between them) is what I would choose if price/availability were not an issue. Home Depot (USA) has this listed for $48 USD ($64 CAD). Home Depot (Canada, where i am) does not carry this switch.

I'm looking for a 1-gang solution. I think what I will do is use a Leviton 5634 ($18 CAD, dual SPST) and wire the top switch to apply power direct to the fan motor, and the bottom will apply power to the thermostat switch (the other side of the thermostat will go to the motor).

The thermostat is mechanical (bimetal) and can't see it having a problem in this configuration.

  • (BTW: you probably could flush-mount a SIB02S, more or less, by using a custom punched KO in the top or bottom of the box you're mounting it to so that everything winds up in the right alignment; the only issue I see with that would be fabricating a trim ring/bezel for the thing, but I'm sure that's doable with a bit of effort) – ThreePhaseEel Jun 13 '19 at 2:21
  • Or to put it another way: is the issue with the SIB02S the idea of something sticking out from the wall, or it not looking like a "standard" wall switch? – ThreePhaseEel Jun 13 '19 at 4:21
  • Also re: availability: have you tried seeing if your local electrical supply house has the Leviton 5685/5686? – ThreePhaseEel Jun 13 '19 at 4:29

A normal switch + a 2-way (3-way for US) will do the trick:

You could use the standard 1-way to select 'on or off' and the 2 way to select 'auto' or 'manual'.

                        P1 of 2W >>>>>>> THERMOSTAT >>>>>  
LINE >>>> 1W >>>>>>> center of 2W                       FAN >>>>>neutral  
                        P2 of 2W >>>>>>>>>>>>>>>>>>>>>>>>  


  • And do all that in a single-gang box? There are no dual SPDT switches as far as I've seen. Dual SPST - yes, and what I want to do can be done with that. – Peggy Schafer Jun 14 '19 at 0:30
  • You could do all easly inside a single 503 box, you'll also have a spare position on the plate. – DDS Jun 14 '19 at 7:48

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