WiFi relay for use with multiple Nest thermostats

I need to control a boiler via WiFi from multiple Nest thermostats, could someone point me in the right direction as I begin my search for information to take on this task? What hardware will be needed and will programming be required. Would the Sonoff Mini or 4 Channel Pro work? Is there reference material available for this task?

Thanks ! ! !

Looks like if you have zoned heating, then you can just use the Nests like normal. Is that the case? If not, they also make a remote temperature sensor for the Nest. Then you still have one controller, and one remote temp sensor. The controller asks the sensor what it is reading, and can decide how to react - heat that other room to the target temperature, heat the house to an average, etc. It looks pretty slick - It can target different rooms as priority according to time of day - living room in the evening set to 74, bedroom at night set to 68, etc.



All of that being said, you could still hijack the signals coming out of the device. It runs I believe at 24V AC and essentially closes a relay to request heat and another to request fan. So build a board behind the Nest to read this, and rebroadcast into your ecosystem via MQTT / ESP8266.

Then you build the new receiver controller board which compares the heat requests from all the different devices and it chooses priority when to run the boiler. It gets complicated pretty quickly since you don’t know the target temperature or ambient temperature for each device without the API (discontinued in 2019); and even WITH the API, it requires internet access to get the data.

But the Temperature sensor is only $39 and works out of the box…

aspork42 and others…

I should have provided more details along with my initial inquiry.

I have twelve Gen 3 Nest thermostats in a building, each of these thermostats are powered by 24VAC from the boiler room. Each of the Nests are located in one of the other rooms along with the zone valve controlled by the local Nest. This zone valve when opened by the thermostat then enables heat to be delivered to that particular room. Due to the original installation, (1970), only two wires were used to provide power to the thermostat, and only two wires were used between the Nest and the zone valve.
Since there is no feedback from the zone valve to the boiler room, this then requires the boiler pump to run just in-case there is a a need for heat in the rooms. Since rewiring the fully finished building seems quite cost prohibited, I am exploring the possibility of using the thermostats WiFi signal to communicate with a WiFi switch or another Nest in the boiler room. My hope is that this device would receive a signal calling for heat in any of the rooms and then close a contact that would start the boiler pump to provide heated water to that room.

I hope this added information helps clarify things, I’d truly appreciate any input that others might have to solve this problem.

Thanks again ! ! !

The Nest is a bit of a walled off garden right now with Google. They are supposed to release a new API later this year. I am accessing it using a HomeBridge plugin. Then I can set it to “away” when I leave my house. So your options are a bit limited software wise to get the heat request status. It would be pretty simple to “man in the middle” the relay output with an extra set of contacts and run that into an ESP32 once for each zone. Then a Sonoff 4ch or really a Sonoff SV or an ESP32 with a cube relay in the boiler room to collect the status of all nodes and turn on the boiler.

I’d be interested to see if 12 rooms ever get “in sync” to allow the boiler to ever turn off for a little while.

Here is a relay from White Rodgers for HVAC systems. Just use this in parallel with the valve and run 3.3v through the contacts into an ESP32.