Thermostat wiring questions

[Hollywood D]

I opened up the furnace today and it’s a 5 wire system. We do not have A/C at the house. There is a humidifier installed and the green wire is hooked into the wiring for the humidifier. Our thermostat is pretty old. I’d like to put one in that can be controlled by a smart phone. Such as a Honeywell or ecobee.

Obviously I just need to hook up the c wire. The current thermostat doesn’t use one so it’s not installed right now.

The question is...since we only run heat will that be compatible with a newer thermostat? I don’t know if the thermostats will get angry if the a/c wired aren’t hooked up. I took some pics for reference. You can see, only the G and W wires are hooked up and that green wire goes to humidifier.

 

[Done That]

Most Wi-Fi thermostats will work in heat only or cool only systems as long as a C wire is present, it is needed because they can't power steal effectively in those setups.

Emerson Sensi covers this on their website.

 

[LS6 Tommy]

I guess that 5 conductor cable isn't the one that goes to your t-stat?

Tommy

 

[brewchief]

It took me a few minutes to figure out how the humidifier was wired, it must be aprilaire with the blower switch control.
You will want to hook up the common if you don't have the A/C wired.
Most thermostats will have instructions show exactly what wires are needed on the outside of the box.

Sent from my XT1254 using Tapatalk

 

[Hollywood D]

Yes it is an aprilaire. The wiring is confusing to me. There’s multiple runs hooked up to it and spliced. But as far as the thermostat goes there’s just the two wires hooked directly to the board.

 

[tyme2par4]

So your thermostat is only using 2 of the 5 wires that are run to it?
If that is the case, all you have to do is take one of the extra wires and attach it to the C wire terminal on both ends.
How is the humidifier controlled? Many new wifi thermostats can also control the humidifier if it's wired. And you already have the wiring in the wall.

 

[Hollywood D]

So this is what the thermostat wiring looks like. The one connected to RC is the red wire. I don’t know how the humidifier is hooked up but they also have that green wire attached to the thermostat, even though it’s not directly attached to the board on the furnace. The yellow wire is the only one missing. It’s probably tucked behind the drywall.

I’m not sure how that blue wire comes into play since it isn’t attached to the board. It’s just wrapped around the original wiring that is attached to the board, same as the yellow wire.

 

[tyme2par4]

So this is what the thermostat wiring looks like. The one connected to RC is the red wire. I don’t know how the humidifier is hooked up but they also have that green wire attached to the thermostat, even though it’s not directly attached to the board on the furnace. The yellow wire is the only one missing. It’s probably tucked behind the drywall.

I’m not sure how that blue wire comes into play since it isn’t attached to the board. It’s just wrapped around the original wiring that is attached to the board, same as the yellow wire.

So it looks like your thermostat is controlling the humidifier. I didn't see the wire nut in your first pictures.
The Blue and Yellow wires aren't doing anything, they are just along for the ride it appears.
So with a new tstat, Red would go to RH, White to W, Green to G, Blue to C and Yellow nothing. Then attache the Blue to C at the furnace as well.

 

[Hollywood D]

In the second pic you can see the green wire is attached to a wire nut and that wiring goes to humidifier. I’m not sure why the blue wire is attached to the thermostat since it’s not attached the furnace. Maybe they just forgot and installed it by accident. I think this should be pretty straight forward

And yes the thermostat is controlling the humidifier. I can shut the humidifier off at the humidifier. It has its own little control box where you can set the humidity or just turn it off completely. But right now it’s set to come on when the furnace kicks on.

 

[Hollywood D]

Well the plot thickens. I did some more exploring and found out there are two sets of wires spliced together. It looks like there is only a 4 wire going from the thermostat to the furnace. But there is a 5 wire attached to the furnace. The blue and yellow wires are not used at all. The red white and green are spliced together and run up to the thermostat. But the blue is not attached at either end. Just coiled up out of the way. I guess the furnace was replaced at some point and either the original wiring wasn’t long enough so they just used a 5 wire piece to complete the circuit.

Which I think confirms my suspicion that the blue wire attached to the thermostat isn’t doing anything. Especially since we don’t have a/c