I'm looking for recommendations for a physical "dummy" thermostat. My HVAC is controlled by a Honeywell T6 Pro. The Honeywell is controlled by a Thermostat Controller that takes into account 4 other virtual thermostats in different rooms. Three of the virtual thermostats do not need any interface.
The fourth one is for the family room I am looking for a dummy device that can be mounted on the wall that can be the physical interface for the family room virtual thermostat. The reasoning is to allow us to easily make adjustments as needed if the scheduler is not adequate, such as when cooking, or when guests are over.
I have everything in a dashboard, but am looking for a "traditional" method to adjust family room temperatures. Something with a dial like the Nest or buttons.
I have an old Nest, but it won't operate without being physically connected to the HVAC. I have a couple of old dumb thermostats if someone has any creative ideas. Otherwise, a recommendation for something to buy is the request.
Don't know about the Nest, but what I think will work is any Smart thermostat. You would connect it to the HVAC power (Red & the "C" wire) but leave the Y's and W's unconnected.
The red and C wire will provide power but without the Y and W the thermostat will not control anything.
The rest will be in RM or whatever app you are using.
I went through the entire zwave thermostat compatibility list and all are not available anymore or are ridiculously expensive. Going through the zigbee list now.
Zigbee smart thermostat.... cheap and battery powered. Not pretty but it works. Also is a full-featured thermostat, not "heat only" as the link implies.
I don't know the answer without trying. But add a second resistor between RC and Y terminals for simulating "Cooling" as well (two resistors should do the trick but maybe just one is enough).
An update: I only had 75 Ohm resistors in the house. Connected up the C and Rh wires from the HVAC and put a resistor between Rh and W. Nest showed that I have a heating system connected! Put a resistor between Rh and Y and then it showed I have a cooling system. All great! It let me set up the thermostat.
Well, until I put it into heat mode. The resistor burned a bright orange and charred the base and back of the thermostat until I yanked the whole thing out. Thankfully, the thermostat still works and there is no charring on the wall. Only a smell in the air.
1K resistors on their way! I should have called Patience Man earlier.
Make sure the resistors are big enough to handle the current (power).
They may get warm but shouldn't get HOT and burn up.
Ohms law... P=E^2/R or 24^2/1E3 (1000). about 1/2watt.
Usually the transformer in HVAC air handlers output about 27VAC RMS though, so a 1 watt resistor would be big enough.
75 ohm would be almost 10 watts!!!! oui!
Also, the heat generated by the resistors will affect the thermostat's reading if they are close to the stat, so make sure they cannot "heat" the air the stat is sensing.
Ops, I am sorry, I forgot to mention power dissipation because this is so obvious for my EE brain. The resistor value could be much higher (will dissipate less power) but without experimenting it is hard to say how high it can go. All what Thermostat is loking for - is a presence of 24V AC on the heat/cool/fan terminals when circuit is not active. This way it knows what exactly is connected.
Yeah, I did the calculations AFTER the burnout and came to the same conclusion!
Update 2: The Nest doesn't even need resistors. Patience Man hadn't arrived yet! Prepping for arrival of resistors, I just inserted 2 inch wires into W and Y and the Nest thinks there is an AC and Heating systems installed. The other end of each of the wires isn't connect to anything!
Hard to believe but it is what it is. If it picks a noise (wire is acting as antenna) this could be very unreliable status reporting. But from the other side this tells me the resistor value could be much higher. Say, even 100K resistor should be OK.
Me being me, I took it a step further for fun. I removed the Y dummy wire -> the thermostat recognized an equipment change that there is no cooling system. Then I hacked the Y connector to be (de)pressed when the thermostat gets attached to the base. Guess what? The Nest recognized a cooling system!
I connected the wire normally so there is no risk of the hack from falling out in the future. Looked for thermostat teardowns, but couldn't find one where the connectors are opened. So, my guess is some tiny contact switch that closes when the connector is depressed.
the burnout and came to the same conclusion!
