SmartThings Community

Switch for hot water heater?



Hi all, I’ve recently moved into a new house and noticed this timer that is set up by the water heater.

I’m guessing this switches the water heater off/on during different parts of the day, i’m assuming to save energy. There is also a solar water heating setup on the roof, which I assume was intended to take over the water heating in those off hours. Still trying to wrap my head around the setup honestly.

But this timer switch in the photo looks fairly straight forward. Is there something I could replace this with that could connect to smart things? I’m thinking ST friendly switch programmed could accomplish the same task without the clunky hardware and have the benefit of control via the app. Is anyone familiar with a switch that could easily swap out for this big clunky thing?

Any input appreciated, thanks!

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It’s the specs on the water heater that will matter, in particular the amps.

SmartenIT make some very nice heavy duty relays that should work fine with most equipment of this type, but you need to check to be sure.

There’s also an Aeotec heavy duty relay, but it’s not weatherproof or waterproof the way the smartenIT is, so it doesn’t do as well in exposed conditions. It’s really meant to be inside a wall.

And there’s a big box GE switch which is meant for harsh conditions:


@JDRoberts Thank you so much for your reply, this is exactly what I’m looking for! So I went ahead and looked up the manual for my heater using the model number (M-2-50S6DS) and found the manual online. Though, I’m not seeing anything in the manual explicitly showing the amperage, it only lists the voltage and maximum wattage, is that enough to determine the Amps needed? Sorry I’m a huge newbie when it comes to electrical/appliances :confused:


Get yourself a Intermatic CA3750

(Jonathan) #5

I saw this new product at the Lowe’s site yesterday. I don’t know if ST can control it, but I am sure something can be written if not. I already came up with a homemade solution several years ago with a high amp relay and using a ge outlet as the trigger. It appears this one will show energy usage if I read it right. Price is a little high though.

(Paul Haskins) #6

These are good for 30 amps.

EZ way - just check what amp breaker it’s on. I have no idea, have not used electric water heater for over 20 years.


Might be new at Lowe’s, but it’s not a new product. It’s the same one linked to in post 2 in this thread. (GE branded zwave devices are made by Jasco, and is a Jasco site.)

Good to know that Lowes is carrying it now in store, That could make some weekend projects a lot easier.


The elk is a different approach. It’s a relay with the plug on the end, but it’s not networked itself. So you would have to plug it into a networked socket. That means it will need a second smart device so that SmartThings can talk to it and that second device will also have to be able to handle the environment. It’s really intended for systems like Insteon which communicate over The home’s powerlines. It does solve some use cases, but if you’re going to the trouble of rewiring anyway, it’s probably going to be simpler to go with one of the other options that have the radio built into them. So good to know about, but I’m not sure it fits this particular use case as well.

(Robin) #9

Looking at the spec sheet for your timer (T100 series) it’s rated for 40A

The Aeon Appliance Switch linked by @JDRoberts in post 2 above is also rated for 40A, so probably a safe bet.

(Robin) #10

Also, the model number you referenced above (M-2-50S6DS) is for the water cylinder and not the immersion heater element within, which come in a variety of different wattages.

I found the following table comparing the wattage options, voltage and resultant Amps:

This comes straight from the M-2-50S6DS installation manual so should be fairly reliable.

Note than none of these exceed 40W so again, the Aeon Switch is a safe bet.

Hopefully the wattage of your unit is stamped on the head of the immersion heater, then you can figure out the Amps to be sure.

(Chris) #11

is there actually gonna be any savings to doing this because i feel like your gonna have to trigger it to come on well before you wanna take a shower or do laundry or anything.


No there will be no savings, that isn’t really the point. Its already hooked up to a dumb timer that turns it on and off on a schedule. The goal is to replace the dumb timer with a relay, program it to the same schedule, and have the added control of turning it on/off from the smart app.


I believe you are correct, my research has landed me in the same spot. I’m going to go ahead with the Aeon 40A switch and hopefully get this done next week. Will post back my results :slight_smile:

Thanks to everyone in this thread, I’m sort of a new comer but this community is seriously awesome :slight_smile:


Oh this is a very interesting option. It looks like the same size enclosure I have now, which might be an easier 1 to 1 swap. I’ll definitely look into this, thanks for the tip!

(Chris) #15

i understand that im just trying to wrap my head around why someone would put a timer on it in the first place and why you wanna keep it and not just wire it hot all the time and be done and spend your money elsewhere on something more useful like a light switch or something.


In my original post I mentioned this is part of a solar water heating system, the hot water is meant to come from the solar tank during the day, thus the timer to shut off the electric heater during those hours.

For more context, I was recently sick and stayed home from work on a rainy day and had no hot water, that’s when i discovered the timer (i’ve only owned this house for ~3 months so i’m still discovering things like this). In that scenario I would have liked to override the timer and flip on the heater from the app, or perhaps set the timer to not turn off the heater until everyone had left the house.


Water heater timers are common in solar systems, often the whole house systems are designed to be as energy sparing as possible. In this case, as the first post in the thread mentioned, this heater probably doesn’t run at times when the solar would be expected to provide the hot water.

This little grey box is actually a timer that tells your electric water heater when to turn on and off each day. As you may have guessed, your solar hot water heater will only heat water during the day (when the sun is in the sky), and your electric water heater will supply the rest. Let’s take a closer look at the inside of the box and what that should look like if it’s set up properly:

(Robin) #18


There are tonnes of reasons for doing this:

  • Use of sunset / sunrise scheduling, instead of a single set of times that constantly need adjusting.

  • on / off based on weather reports to cover cloudy days. (IFTTT)

  • on / off based on an external lux sensor

  • It can turn off in the middle of the night when people are sleeping, but set to warm up again before you wake. The existing timer only has one on/off per day which would prevent this… Immersion heaters are not cheap to run!!

  • It can be programically linked to a 2nd device controlling the solar array pump. This will ensure you’re not pumping electrically heated water through a cold solar array (you can loose heat if conditions are wrong).

(Daniel Ionescu) #19

This is a heavy duty timer. Used to be used mostly for outdoor lighting. Based on your picture, wires look more like #16AWG so it’s not cutting power to the heater but only acts as a control switch (similar to a cut-off switch). I believe you can replace it with any z-wave controlled relay (probably dry contacts) but you need to check wiring just to be sure. Electrical code mandates #12AWG for 20Amp circuits and #14AWG for 15Amps. Wires in the picture look more like rated for 10Amps. As far as outdoor ratings, most relays will work outside provided they are enclosed in an outdoor enclosure. You can take out the guts of this timer and keep and use the box. And you already have the wires to reuse. Problem is I don’t see a neutral (white wire) which is required by z-wave devices. Possible though that they used another color. I see a white pigtail on the red wire.
It has to be a neutral as this timer has a small motor behind the panel. Time interval is adjusted by moving those mechanical stops. and as the dial rotates, one stop will make a mechanical contact while the other will break it.

(Daniel Ionescu) #20

Water heater timers are indeed common in solar systems. However, the installer shoud’ve had the solar control panel interface with standard water heating system. Otherwise you have to change timer settings depending on sun/rain/summer/winter/day lengths etc. Solar systems also have their own water tank. If water temp is high, stop the other system. If water temp is low, start the other system. No need for timer.