Level of difficulty: installing a wireless thermostat for my house?

We had forced air heating with an oil furnace and wanted central air, but the existing ductwork was too small so we ended up putting in an attic blower and ductwork upstairs and downstairs we have two mini-splits.

This means I can use the mini-splits to heat the downstairs during the winter.

Problem is that the thermostat for the furnace is downstairs and I'd like to be able to heat the upstairs to a decent range say 70 using the furnace and then downstairs have the mini splits make up the difference. This will work out better for me overall I think because I have solar and so electric is cheap (or relatively so over time).

I'm not great at understanding electrical diagrams and what not, but with some Internet I think I've worked out that the furnace has a five wire terminal and right now the thermostat I'm using doesn't have a C wire running to it. The only thing connected to the C wire terminal is the power humidifier which is also connected to the R terminal so I assume it powers itself on whenever the furnace comes on.

I wanted to put this guy in.

https://www.amazon.com/Honeywell-YTH6320R1001-Wireless-Thermostat-Programmable/dp/B001O4F8Y4

I'm assuming I would just need to take the wiring going to my current thermostat and add another wire coming from the C terminal to this? It seems relatively easy since the wifi transmitter would just mount in the basement on a beam so I wouldn't need to go particularly far with the wiring.

Am I far off?

Does your existing thermostat control the cooling? Or is that a separate thermostat?

Robbie said:

Does your existing thermostat control the cooling? Or is that a separate thermostat?

That's separate. There are two cooling systems, the one feeding the minisplits downstairs and the one feeding the air handler and ducts upstairs.

And then there are two heating systems. One is the furnace which has ductwork going to all rooms. And the other is the minisplits that can heat the whole downstairs.

Help!

So, going from the top of my head and I am not an HVAC guy. But I THINK that if you don't have heat and cool on the same thermostat you don't even need the extra wire you're planning to run.

Thermostats have wires for power, ground, heat control, cool control, fan control. Some larger systems may have other zones. Sometimes the fan control wire is skipped and the fan just comes on with heat and cool. 

But I think you're on the right track and may get away without the extra wire.

The wireless thermostats require a C wire for constant 24v power. Or at least this one does, but I haven't found any others that don't.