Thermostat for underfloor heating AND cooling

Hello all,

I am looking to upgrade my analog Thermostats with something I can use with openHAB, and I am unable to find what I need. Maybe you can help?

What I have:

  • underfloor heating/cooling, powered by a heatpump. So the water is made hot in winter, and cold in summer
  • Analog thermostats that provide 220V to open the valves. These have a little switch to change between modes: in “heating mode” they switch on below the desired temperature, in “cooling mode” this is reversed and they switch on when the temperature is above the desired temperature.
  • an existing z-wave network

What I want to do:

replace the existing thermostats with something that can:

  • be connected to 220V
  • display the desired temperature
  • switch on the 220V for the valve
  • can be made to change from “cooling mode” to “heating mode” via openhab
  • can be made to change the desired temperature via openhab and/or the thermostat controls

As I already have z-wave devices it would be nice to have z-wave thermostats also, but this is not a hard requirement. I would be happy to have anything at all.

Does anyone know hardware that would fit my needs?

Hey HiGer,

I have 12 underfloor heating zones that i upgraded around 1 year ago. I had the old 220v 3 wire analog thermostats in each room that needed updating. I did this using very cheap sonoff basic switches, and wired a dht11 temp sensor to the spare gpio on the board. The 3 wires on the thermostats are basically on and off. I flashed the sonoff basics with tasmota and use mqtt and openhab to control the heating. Its actually incredibly simple system as you just need it to turn on and off when it gets to your desired temperature in my case 21c. I have additional sonoff zigbee temperatre sensors in each room so I can get an average temperature in each room as the thermostat was 1 0r 2 degrees higher and the second thermostat is the same but lower. If you have lamps with sonoff basic switches on them then they can also be your second temperature sensor. In my opinion or situation, there is no need for a display as it should always be 21c or above. Each thermostat probably cost £10-£15 each to make you just need a sonoff basic £5, a dht11 temp sensor £2, and a sensor wall box £7. There is a great feed on here called Boilerplate, I recommend reading that and I’m more than happy to share my items, rules, things files.

Please turn off the electricity before doing any work on your thermostats

I’m in the UK so we don’t really do cooling…

This is actually really interesting. If I understand this correctly you are simply using a switch that is controlled by oH, and a temperature sensor value reported to oH, and the rest is software. The main difference to the full blown thermostats is that it does not work standalone. But that is more of a bonus for me, as it gives you full flexibility, and my openhab on the pi4 has been running rock solid without any issues at all. It is even rather simple to implement the switch between heating and cooling mode.

I am almost sold on that idea already. Lets see if anybody has another, ready made solution, but this here is definitely something I could imagine to implement.
I would only have to convince the one cohabitant with veto-power that:

  • yes, I will finish this project in a timely manner, promise
  • no, you do not need a temperature control and display in every room. The smartphone is way more convenient anyway.
  • Its a lot cheaper, don’t you think thats good?

The best thing to do is make a test switch and run it in a room that doesn’t matter if it fails. I’ve still got the old analogue switches in the bedrooms and the new switches ‘piggy backing’ them so if they fail then at least the old ones will kick in. They work flawlessly.

Once you have it all going through Openhab you can use the Network Binding to ping the thermostats to see if they go offline, if they do then you can send a notification to Telegram etc etc

I also have it connected to my security system or door and window contacts to drop the set point to 10c when the doors or windows are open, then when they close to put the set point back to 21c but after 20 minutes. Its endless.

You may want to look at the link below. Most 'Stats are either heating only, or cooling only, so you need to choose from the limited list of those that can do both. Of the thermostats listed on the site below, at least a few of them can be integrated into openHAB

Ok, thanks Andrew for that link. Looks very nice. But, man, those are pricey. The winner of that review goes for something like 400 Euro. I need to replace 14 of them. For that kind of money I could hire someone to run through the house and adjust the old thermostats for me when needed. (Actually, when I think about it: I could hire someone named Alexa and yell at her all the time to change the temperatures… :grinning_face_with_smiling_eyes:)
And in the end they would most likely be overkill on one side, and would want to do much of the functionality that I want to implement with rules in openHAB by themselves. Some specific things I thought about would not even be possible. For example I thought about leaving the valve open until the temperature is one degree over the target temperature if there is excess power available from the photovoltaic to run the heatpump. Easy to implement with a rule.