Temperature based water heater control AKA avoiding the cold shower dance

Hi All,

I’ve want to setup a z-wave automation and I have done a bunch of searching and so far I haven’t been able to find an approach that will accomplish what I want. I’m hoping someone on the forum know of a device/control methodology that will allow me to accomplish it.

  1. I have a solar water heater on my roof that typically heats my hot water to a comfortable temperature most of the time. However, we get a lot of rain/overcast skies here and when that happens the water doesn’t heat up. Usually the first indication of this is when you step into the shower that night :o resulting in the 30 second cold shower dance.

  2. In order to avoid scenario 1 above one needs to step into the garage, check the in-line analog temperature gauge on the water heater, (see attached photo) and if it too low flip a switch on a timer box, (see attached photo) to turn it on. Of course one has to remember to do this on days when the solar heater doesn’t do it job or one again gets to do the 30 second cold shower dance.

  3. What I want to do is A) Replace the timer box with one that is z-wave controlled, (this part is easy) and B) Replace the in-line analog gauge with a Z-wave temperature monitor, (not so easy in that I can’t seem to find such a device).

I can use this to replace the timer box

But I can’t find anything z-wave that will replace the in-line analog temperature gauge

The goal is that the Z-wave temperature gauge sees that the hot water temperature drops below xxx degrees then it will kick on the water heater, once the water temperature reaches xxx degrees or above then it will turn it off. Hopefully this will prevent the cold shower dance and save some energy as sometimes when you turn on the water heater you forget to turn it off so it keeps running long after one’s shower is done.

Also, I’d like to try and do this without spending a small fortune as my accountant, (wife) wouldn’t like it.



I have not found any gauges for this. There’s mysensors.org I think or something like that to build your own. I wanted a zwave low pressure gauge for my pool filter but can’t find anything like it anywhere. Odd with all the devices there’s no gauges available.

If you don’t use it that much, maybe a tankless water heater would be a more economical choice for your home as you would not have to turn it on and off each day?
As I understand it now from your pics the water coming from your solar system to the water heater is 120F? That should be enough to keep the heater from kicking on even when the heater is turned on?
I am not sure if I would trust my water heating to my Vera on a daily basis.
Seems like your set up of preheating the water before it enters the water heater would be the most economical. The only thing I would recommend is a natural gas heater as they are dirt cheap to operate unless you get your electricity from the sun.

in order to measure the temperature of the water I use the following:

1x Fibaro Z-Wave Universal Binary Sensor
2x Waterproof DS18B20 Digital temperature sensor

if these are connected the right way I have inside my Vera 2 sensors.
(good explanation: [url=http://www.dreamgreenhouse.com/reviews/2012/fibaro_us/index.php]Stylish and environmental smart home design & build)

In this way I check the pool water temperature. If the water in the homemade sun-collector gets above 32 degrees C it will turn on a waterpump.
Below 29 degrees C it switches off the waterpomp and enables the filter pump again.

This is not always 100 % reliable. That’s why I set a ‘reconfigure’ every night.

I will test this again next summer.

Hi All,

Thanks for the responses:

Tomtcom - That has been my experience also. Although I had a idea and decided to test it. My water heater pipes are wrapped in insulation so I decided to take a temperature monitor I have with a remote probe, (Not Z-Wave unfortunately) and stick it under the insulation and compare it’s readings against the analog gauge and my Klein multi-meter with thermocouple. My results were encouraging:

Analog gauge: 116 degrees Fahrenheit
Temperature monitor: 112 degrees Fahrenheit
Multi-Meter in water from tap: 116 degrees Fahrenheit

So the temperature monitor with remote probe was only 4 degrees lower than the other two which were in direct contact with the water. So I then started looking for a Z-Wave temperature monitor with a remote probe AND digital display and ran into another wall. There is a lot of things out there that look like they might do the trick, but either don’t have a display, or don’t have a remote probe etc. So I spent another fruitless 4 hours scouring Internet for a device that will do the trick and haven’t found exactly what I’m looking for. I did find the Everspring 814 which is exactly what I want, but alas no remote probe.

There are a lot of almost solutions that I can “make” work if I want to “customize” the hardware. To say that soldering irons and I have a love hate relationship is putting in mildly, lol

Jamr - Great thought :slight_smile: Unfortunately, we do use it a lot and since I have a solar water heater, going tankless would kill the energy savings I get from it. It the picture it is 120 degrees, but it was a sunny day when I took that pic. When it’s overcast and/or raining for days on end the water temp get as low as 75 degrees, which is a great temp when your taking a swim in the ocean on a hot sunny day, but not such a great temp in the shower first thing in the AM or last thing at night. As far as gas goes, it’s not available in my subdivision and my HOA would have a fit if I tried to install a large tank in my backyard, lol. As far as trusting the Vera on a daily basis it wouldn’t be every day and I can just have it send me a text alert if the water gets above or below a certain temperature. Also, it would only be at certain times, ie if at 3:00 AM or 8:00 PM the water temp is below 100 then turn on the water heater until it reaches 100 etc.

A.Ardon - Your solutions is the closest to what I want that I’ve run across, but there is that love/hate thing with the soldering iron and the whole customizing. When I hack hardware then I usually get something that starts having all kinds of intermittent issues that I spend more time troubleshooting in a month than I would have spent all year just walking into the garage and flipping the switch on and off as needed, plus the wife, being the dear sweet analog thing she is, tends to read me the riot act when that contraption I cobbled together stops working and she gets a cold shower. :slight_smile: Also, I need something with a display so my wife can look at it form time to time to make sure the pesky computers actually know what they are doing, this is a woman who won’t believe Excel when it sums numbers and has to break out a calculator just to be sure and no we’re not in our 90’s :slight_smile:

You would think with all this high tech Z-Wave hardware available someone would have thunk to make a simple Z-wave temperature sensor with a remote probe and a display that doesn’t cost an arm and a leg - go figure.

I’m going to call around to some vendors this week and see if any of them might have a remote/external probe with or available for their devices and just neglected to mention it on their webpage. Who knows I might get lucky.

If I run across anything I’ll update this thread and pass it along.

Again, thanks for the responses.


Good luck my friend. If you hear anything let us know. I still have interest as well. I’ve scoured as well for many fruitless hours. Maybe we can get another home automation startup to produce another hub and the same set of sensors and devices already available (sarcasm).

Those temperature sensors are designed to work with the Fibaro Universal Sensor. So not really customizing, just plugging in.

If you want a display, you might consider 433 Mhz instead of z-wave. See the sub-forum for “USB RFXtrx Transceiver Plugin” and this is also a plug-in for the IP version. Then you can use off-the-shelf 433 mhz products - including temperature and pool sensors, some of which have built-in displays or display to a wall unit. For example I have LaCrosse wall clocks that have indoor/outdoor temperature and humidity display - the outdoor unit uses 433 mhz and I can read that temperature and humidity on Vera via the USB receiver and the plug-in. I monitor other temperatures in the house via remote units that are not even paired to a wall clock and those remote units have their own small display of the temperature.

See the user guide for sensor models that are supported (http://www.rfxcom.com/ - switch to English download RFXtrx User Guide.pdf). The new Vera Plus is rumored to support 433 mhz natively, and the USB unit is not cheap, but the air temperature sensors can be found inexpensively, and I assume the water temperature are available…

I agree this sounds like a perfect place for a TANKLESS heater.

It has built in inlet and outlet temp probes and will use just enough energy to get you from what ever your inlet temp (since you varies so much from day to day) is that day to the same consistent outlet temp. If the inlet it high enough the water will pass right threw without using any energy, if its not the logic of the tankless will use just enough to get it to your preset temp. Most if not all thankless have digital temp readouts and mine even has a remote so I can change it on the fly from the restroom or where every you mount the remote or remotes.