Can anyone recommend a thermostat upgrade that doesn’t require a C wire for my central AC and gas heating system?
Asked by Amelia Mitchell 
5 months ago
Last Updated: June 20, 2024
I’m thinking about upgrading my thermostat, but the one I checked out said I need a C wire. To be honest, I’m not really sure what I’m doing and could use some suggestions. Here’s what I currently have: central AC and gas heat for both the house and water.
You’re missing a C.
The red wire (Rh) is used to signal for heat
The yellow wire (Y) is used to signal for cool
The W wire connects to the Rh or Y, depending on what the thermostat is requesting.
The unused blue or black wire might work for C, but you’ll need to check inside your furnace to see where these wires go.
Got it. Look for the other end of this wire in the furnace. Check if there are just four colors or if there is an additional one that is not being used. If there is, connect it to the C terminal in the furnace and then extend the wire to where the thermostat is located. Find the same color you connected to C and use blue if possible. That’s the standard procedure. If you don’t have an extra wire, some thermostats use batteries instead or you can add a module to power them with the existing wires. For example, Ecobee offers that option.
Yeah, the best course of action is to inspect the wires on the heater.
It seems like you don’t have one. I used a spare wire for mine. I simply removed the furnace cover, located the wires, connected the unused one to the C terminal, and it worked perfectly!
Right on!
The thermostat has 5 wires. If you take off the mounting plate, you’ll probably see a 5th wire wrapped around or spliced. There should be some slack in the wire, so carefully pull it out of the wall. Find the 5th wire. Head to the furnace and you’ll find the other end of the 5th wire wrapped around that end too. Look up the wire diagram for your furnace model and connect it to the common terminal. It’s actually pretty simple, trust me.
Rob’s thermostat wire can range from 2 to 10, depending on what was available at the time. Right now, he has 4 wires (24, cool, heat, and fan). There are adapters available, but he might not know how to properly connect them. It’s best to have someone else do it to avoid blowing a fuse and needing additional help to get it working again.
Is lucky if he has that extra wire tucked away in the wall. The best way to check is to see if there is a spare wire coming into the furnace.
Is right. I haven’t really worked with anything other than 5 wire systems before. It’s pretty much all we used in our trucks.
Got it, . I’m not an installer, but if I were, I’d pull something with extra wires for potential future expansion or in case some wires malfunctioned.
Hey, , that’s exactly what went down at my place – someone shoved the blue wire into the wall and attached a 4-wire piece at the end. I began pulling gently and lo and behold, there’s a blue wire there.
When I took out my old thermostat, I realized I didn’t have a C wire. The new thermostat claimed I didn’t need one (which turned out to be mostly incorrect). Fortunately, I found an unused wire in the thermostat wiring after removing the old one. I connected it to the C terminal and repeated the process at the furnace. So, I recommend pulling out the wires a bit to check for any extra wires just in case.
There might be a wire laying around that could be hooked up for use.
For a smart thermostat, the ecobee premium model includes an adapter that eliminates the need for the c wire.
Is there a warranty on your air conditioner?
It should even fit on the same base plate