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I have an old Honeywell thermostat-type switch that controls the heater in the bathroom. Teenagers frequently forget to turn it off and so it runs for hours. I want to replace it with a push-button timer switch to prevent this.

The heater unit in the ceiling also has an exhaust fan connected to a typical light switch. It is on a different breaker than the heater.

The new switch has three wires on the back: green for ground, red for load, black for hot. So far so good.

new switch

When I removed the old switch, I found the following setup

existing wiring

The two black wires connected on the switch are labeled L1 and T1, while the two red are L2 and T2. Obviously the bare wire is the ground that I would connect to the green on the new switch. I believe I should connect the red wire on the new switch to the white wires. I'm confused about what to do with the existing black wires and the black wire from the new switch.

Needless to say, my electrical experience is mostly limited to light fixtures and ceiling fans. This house was built in the 40s and the bathroom was obviously a later renovation, so I have no experience with how it's wired.

Am I correct in what I think about connecting the new red to the existing white? And what should I do with the black wires?

  • Can you post the voltage and wattage ratings for this heater? I suspect you may need a different timer and an extra box for this job if you're insisting this be a pushbutton timer... – ThreePhaseEel Jan 21 at 0:42
  • Came with the house so I know very little about it. Directions worked though. Once I found my multimeter and determined which of the two black wires was hot...it's been in business for a couple days with no issues. – jerH Jan 22 at 13:12
  • My concern is that this heater might be 240V, and the timer switch you put in isn't rated for that... – ThreePhaseEel Jan 23 at 0:33
  • If that were the case there would be a double breaker in the panel correct? – jerH Jan 23 at 19:58
  • Yes, there would be a two-pole breaker in the panel if it was a 240V heater – ThreePhaseEel Jan 24 at 0:03
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NO, NO, AND NO!!! RED DOES NOT CONNECT TO WHITE. The "hot black" from your new switch goes to the black wire in the box that is feeding the circuit. The "load red" from your new switch then goes to the remaining black wire in the box. Yes, the green wire goes to ground.

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    Jack's comment is likely correct. Do you have a meter? Unscrew the nuts on the black bundles and check for voltage between each bundle and ground. The bundle with voltage goes to hot black, the other goes to load red. – Chris Cudmore Jan 19 at 18:48
  • This is why I asked :) Thank you. How do I determine which of the two black wires goes to the black on the new switch? Underneath the L1 label on the back of the old switch is something that looks like a sine wave, while underneath the T1 is something that looks like a square wave. Am I correct in assuming the sine wave (L1) is the current and would go to my new black, while the square wave (T1) would then go to the new red? – jerH Jan 19 at 18:49
  • I was typing as you posted that Chris. I own a multimeter, but I admit to having rarely used it. So I would need to turn the breaker back on, turn the heater on, and then look for voltage between the ground and each of the black wires (L1 and T1) respectively? – jerH Jan 19 at 18:51
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    @jerH With the power off, remove the wire nuts from the black wires and separate them. Then turn the power back on and do your testing being careful not to touch the wires. after you determine the feed, turn off the power and hook up the switch. – JACK Jan 19 at 19:00
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    @ Jack is correct the hot black goes to the switch black the other black to the red on the switch. And you already had the green ground figured out. – Ed Beal Jan 20 at 17:34
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The original Honeywell switch was a 2-pole switch. And typically with Honeywells, one pole is thermostatically controlled, and connects both blacks if it's too cold. The other side is a simple on/off switch that is regardless of temperature; both reds are connected unless the switch is in the OFF position. And the thermostat doesn't care whether it's switching 240V, 24V or millivolt. So toss it in your parts drawer; you never know.

Having a powered switch raises a lot of questions

Sanity-check that this is a legit product. It's a pushbutton (not a wind-up) timer, so it needs power to power itself. Normally, these devices use a neutral wire for that. Be cautious about ones that don't; If it has a UL, CSA or ETL listing with a 7-digit file number, then it's probably OK. Indeed you have linked the device in a comment, and it looks great. Clever GE!

Now we need to look at the heater's voltage. Absolutely nothing about your picture tells us whether your heater is 120V or 240V. The whites could be neutral, or they could be the other pole. This device is 120V-only and won't appreciate 240V none too much, since it will have heater voltage across it when the switch is off. The heater's nameplate will tell, or shoot us a pic of the breaker with a few other breakers around it.

We also need to check the unit's capacity. This unit has only a limited capacity of 800W. Good chance your heater is larger than that. This needs to be evaluated too - and nothing else will do but looking at the heater's nameplate rating.

You'll also need to identify which black is the supply hot wire; that goes to timer black. The other black goes to timer red.

All in all there are a lot of standing questions here.

Or just use a twist-knob type timer

Boom. All the above issues go away! Easy peasy.

The common twist-knob timer, requires only a 2-wire connection -- those same 2 wires already connected to the existing thermostat. The energy source for the timing mechanism is you. Its capacity is 2400W, we don't need to care about whether this is 120V or 240V, nor which leg is hot. Done and dusted.

Honestly, that's the way I'd go, unless there's some showstopper reason why a pushbutton type is required.

enter image description here

These types are available in a wide spread of time intervals between 5 minutes and 12 hours. A "Hold" position (stay on indefinitely) is an option. Obviously you want to avoid that option. I caution you to use one with a long enough time, so children don't have to set it twice. It's possible to trick these into never shutting off, so don't give them a reason!


This. This is why I hate pushbutton types. Having the switch twist the knob for you means the switch must be powered, and getting power to a switch raises issues that DIY installers aren't ready or interested in dealing with. A pox on all of them, the switches not the installers. Humans have wrists, they can twist their own knob.

  • The new one is a GE product purchased from Amazon. GE Push-Button Countdown Timer... amazon.com/dp/B007BJULYS?ref=ppx_pop_mob_ap_share. The docs say it needs a few minutes after installation to charge prior to use – jerH Jan 19 at 22:51
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    @jerH Well, that supports the "leaks power through the load" theory. I'm comfortable with that design. Whoever thought a huge company like GE (that isn't 3M or GM) could ever innovate like that? – Harper - Reinstate Monica Jan 20 at 1:08
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    @Harper-ReinstateMonica GE has, at times, in some divisions, been actually very innovative. My evil twin & I got some scholarships in college from GE - only sort-of-requirement was to go on a field trip to visit a GE factory - which was pretty cool. But that was > 30 years ago... – manassehkatz-Moving 2 Codidact Jan 20 at 19:34

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