Let me preface by saying Ive not done deep research, but intend to, just wondering if anyone had similar.
My grammas house has two thermostats. One controls her central air and the other controls her (hot water radiator) heat.
It’s my understanding that I can shift the wires and use one thermostat to control both (and in this case I believe Id need to run an additional wire to power it)
Want to make sure Im not crazy before ordering the thermostat and taking everything apart.
Correct you can, but I think you need C to come from the air handler. You don’t have that so you would need to run another wire. There is a schematic that Wyze has been giving out to use the c wire adapter for dual transformer but it didn’t work for me
Gramma is not going to be happy with you running new wire on or inside her wall. 
That Honeywell on the left takes batteries and I don’t think the heater thermostat takes power at all. You’ll need to add transformer power somewhere I think. Hope I’m wrong for your sake.
You arent wrong.
No extra wires hiding either.
I didnt expect it to be easy. She had the central air installed a few years ago and they cheated their way around… the attic unit is connected to the light switch that controls the attic light so I’ve got to run wires anyways.
And for funsies, the attic light switch used to be the living room light switch so its right next to the hall light switch. Fixing that so people stop shutting off the AC by accident is my main goal.
That’s kind of you then. It will be nice to clean up that wall too. I just hope the new thermostat is reliable. Good luck.
Edit: what’s already a little crazy is the Honeywell on the left ALREADY has heat/cool capability. The AC guys could and should have moved the wires then! You should probably try it now before you even order a new unit, just in case there is something even crazier going on…
Great minds think alike 
It works with just the honeywell, but that “was too confusing” so its back to two at the moment…
Wait until Gramma has to deal with the Wyze app.
She has cameras, plugs, bulbs, and door sensors, I didnt think it would fly but apparently its easier than the remote for the cable box.
I need to do more digging.
She wants to keep the circuit for the AC off when not in use so I cant run C wire from there, and it doesnt appear I can run it from the furnace either. (Photo attached) and at first glance I cant use external either because it will occupy RH and RC.
Thought it was a given you’d be plugging in a new transformer somewhere (anywhere) and running new wire from it…
Just trying to find an easier (safe) way out. Already ordered the transformer, but not looking forward to it, lol.
