Hi all, I’m wanting to add smart thermostats to my HA installation to control our hydroponic heating system (we don’t have A/C where we live, so this is heat only). A pretty simple low-voltage 24V system, i.e., no fan, no A/C, etc. I’m currently searching for the best Z-Wave option, and wanted to know if anyone else has any experience integrating thermostats with this kind of heating system. I haven’t ruled out WiFi, but would prefer Z-Wave if possible. I don’t know if there would be any additional integration required for the thermostat, other than the existing Z-Wave, unlike WiFi (since I currently have only Z-Wave devices, no WiFi).
If anyone has had any experience with this, or can offer any suggestions, I would really appreciate it. TIA.
Yes, pretty simple. Currently have Honeywell mercury switches (TD822D), two-wire, that connect to zone valves (5 of them). One thing I’m trying to determine is, if this is powered all the time (and therefore can take a powered thermostat), or if this old thermostat just completes the circuit and therefore will require a battery-powered replacement. I suspect the former, but am still researching it.
So, after researching some more, the original thermostats aren’t powered, but just complete the circuit back to the zone valves and therefore the controller which triggers the circulating pump and the gas switch for the boiler. A third “C” (common) wire would be required at a minimum to power a smart tstat (although battery is an option). Luckily, the wiring I have to each tstat is a three wire conductor, the third wire is just not used. All I need to do is figure out if I can somehow connect that wire to my controller’s 24V transformer in such a way as to provide continuous 24VAC while not frying my controller. The unit is from 1983, so common wires for powered thermostats weren’t even a thing then. There should be a way to solve this…
You can use temp sensor and switch. You can combine the switch and sensor as a thermostat in HA or use automation with temp as trigger for switch on/off
Homeseer HSM200 is multisensor.
You may have use for luminance function of this as well as temp.
Trane XR524 is good zwave thermostat
You should be able to properly power it and control heat only system.
Very much so. There is a “C” terminal somewhere on your zone controller. As you state, the thermostat is just a switch. One wire (“R”) goes (ultimately) to one side of your 24VAC transformer, the other (“W”) brings that power back to the controller when the “switch” is closed (thermostat calls for heat.)
The “C” wire goes to the other side of the 24VAC transformer. Given the vintage of your controller, it may or may not be labelled. For mine I called the controller manufacturer to confirm. But there’s usually a schematic somewhere, or you can trace wires, or Google it. You’re probably not the only one upgrading to smart thermostats.
Does “AK” in your name suggest Alaska? At any rate, if you’re in a climate where heat is more than just a luxury, I’d recommend against depending only on HA to control it. It’s a great system, but it’s not really ready for critical systems yet.
My own system uses Honeywell Smart WiFi thermostats, with the HA Honeywell integration to control them. This leaves the Honeywell cloud-based app as a backup. Plus they run on their own if the cloud isn’t available. I’d prefer local control, but this is what I ended up with and I’m OK with it.
Another option might be to simply leave your existing thermostats, and add HA control. Some small relays driven by the GPIO pins on a RPi could close the switch connectors at the zone controller based on automations in HA. You could set the existing thermostats at some minimum temperature as a backup if HA fails.
Sorry to go on at length. I got into HA primarily for monitoring and controlling my heating system. I live in a climate where loss of heat could get very expensive, even life threatening. So I’ve got some experience here.
This would also be easily fixable using an esp and a relay. Combine it with a temp sensor - which may also be on the esp, or may be anywhere in the house. With esphome you can also get the advantage of PID control.
@tmjpugh & @nickrout Thanks for the response. One thing I love most about HA is that multitude of ways in which any problem can be solved. My goal is similar to that of CaptTom, in that I don’t want to rely on HA to have full control of my heat, since any failure could be catastrophic. All of my HA automations fail over to the previous manual control/response, if HA disappears completely. All my ZWave devices are for security, monitoring, safety, and convenience, but none are actually required. That is a basic requirement for me.If I ever leave this home, things will still work, just not as conveniently, e.g., light switches will revert to manual switches. I’ll take a look at the Trane!
@CaptTom Yes, AK is Alaska, and I, like you, can’t rely on HA to control my heat. I need a tstat that will fail over to manual operation which, at the least, will maintain some level of heat. I read comments on one of the Honeywell ZWave units that stop working following a power outage, because it was waiting for the user to reset the date! That kind of behavior is unacceptable. I think you are correct in that I only need to use my third (unused) wire as the C wire by connecting it to the C terminal on a smart tstat to provide full-time power and the other end to the White wire on the transformer. My unit has an external transformer because I have 5 zones. I may post some ideas on a HVAC forum to see if I cant get any heating experts to help me not fry my controller. It should be simple, but somehow it never is, so maybe I’ll wait until summer to actually try this!
The GPIO idea is interesting, but may be more than I need, especially if I can get the other thing to work.
Just measure the voltage between R and what you plan to use as C. It should be 24VAC. Be sure you’re on the AC scale of the right range, depending on how your meter is set up. There’s no guarantee that whoever set your system up followed any wire color codes. With a simple two-wire system, it doesn’t matter which is which. It will matter very much when you add a C wire.
My Honeywell thermostats are WiFi based. But I like the idea of Z-wave, if there’s an integration for HA that allows fully local operation. The fewer components you need to rely on the better. As long as the thermostat can continue to operate with no external devices, and as you say, can recover from a power outage, that would give you exactly what you want.
Presumably, you’re designing for a power failure and internet outage at the same time, and would need a generator to run the heat anyway, so powering HA would be trivial.
Another option might be to simply leave your existing thermostats, and add HA control. Some small relays driven by the GPIO pins on a RPi could close the switch connectors at the zone controller based on automations in HA. You could set the existing thermostats at some minimum temperature as a backup if HA fails.
That is/would be my option.
I simply added a Z-Wave Relay (Aeotec) to control my furnace and then use an average of 4-5 different temperature sensors as my temperature sensor, all through the generic thermostat platform.
I’ve used variants of this setup (Zipato >> HomeSeer >> Home Assistant) over the past 3-4 years and in general it has worked very well.
I don’t have a traditional thermostat as a backup (yet - three years later) but was going to use an old fashioned mechanical thermostat (no batteries to change) as freeze protection in case the thing goes down while traveling.
