I have a Honeywell T6 Pro that I have been meaning to get around to installing. I finally started looking into this today, and pulled off the faceplate on the Nest I'm replacing to look at the existing wiring. I'm not sure that what I find there will work w/the T6.
I have a Rheem gas furnace and AC:
Rheem Furnace
Name: Rheem RGPN-07NAMER - Classic Series NOx 80% AFUE Single-Stage Upflow/Horizontal 75K BTU Gas Furnace
Item Number: RGPN07NAMER
Manufacturer Product Number: RGPN-07NAMER
SKU - PIM Number: 1369225410943
Item Number: 230628
UPC: 662021215674
Equipment Type: Furnaces
AFUE: 80.0%
CFM: 1330
CFM: 11
Heating Capacity: 60
Air Flow: Upflow / Horizontal
BTU Input: 75000
Voltage: 115 VAC
Full Load Amps: 7.1
Phase: Single
Cycle/Hertz: 60
Minimum Circuit Amps: 7.1
Ignition Type: NOx
Motor Type: PSC
Speed: 4
Fuel Type: Natural Gas
Gas Connection: 1/2" [12.7 mm] N.P.T.
Blower Motor HP: 1/2 HP (updated to 3/4 HP in 2021 due to remodel)
Product Family: RGPN
Here's what I currently have connected w/the Nest:
And looking at the wiring at the furnace board...the blue and brown wires are not used and are wrapped around the wiring bundle coming from the thermostat. The white, green and red go directly to the furnace board, and the yellow is tied off w/another red wire in a wire nut and then a white wire from that group goes to the board.
Are the four wires (Red/Green/Yellow/White) going to be enough into to connect the T6 to work w/my setup? The only area I know less about than HVAC is Quantum Physics, so really appreciate any help.
If you tug at the wire bundle in the wall currently connected to your nest, I think you'll find a blue and light brown wire tucked back there too -- blue is commonly (by conventional standards) used as the "C" wire, so that would be super nice to have at both ends. If there aren't a blue/brown wire tucked back there, then we need to re-assess what's connecting the stat to the furnace board.
In the second pic, I'm pretty sure that 18-3 (w/ unused green) on the left comes in from your exterior Air Cond condenser (since the red & white connect at C and Y).
What I can't figure out is that 18-2 on the right and what the heck is going on with those Y connections... There Y1 from the stat is nutted to a red going somewhere, but then coming back to Y on the furnace board via white... Where does that 18-2 go / what does it connect to?
I agree w/you that the bundle will include the blue and brown at the top by the thermostat - I never did anything to remove any wires from that bundle. For some reason they aren't in use currently so the Nest evidently isn't using them/doesn't need them?
The 18-3 w/the unused green exits the furnace on the left and runs up the side of it and exits into the attic, which leads me to agree that it's heading off to the AC, as the compressor is on that side of the house and its connections run up the side of the house and into the attic. It's the wire in the pic below running up between the two copper pipes:
The 18-2 also exits the furnace enclosure on the left and runs to the area under the furnace, where there is a pump to remove excess water condensed from the air by the AC condenser, IRRC.
Below is a pic that shows the whole kit-and-kaboodle...a mess of spaghetti:
Good news about the blue (C) wire! Yeah, you could be using that now with your nest too - connect at C on the stat (Nest or T6 or any other modern stat), and connect the other end of the blue at C on the furnace board. You can connect multiple wires under those screws on the furnace board - typically there's 2 max (one on each side of the screw), but as long as they securely tightened down, you're golden. In this case, you'd have the blue wire and the existing red wire from AC connected at "C" - that's totally cool.
I kinda figured that 18-2 was probably going to either a pump or safety-switch -- that's just not a pump wiring setup I'm familiar with, but I know just enough HVAC stuff to be dangerous - I'm most definitely no expert!
Well, heck, I don't have a T6, but I sure think you'd be good-to-go with one, especially since you know you have a C wire readily available to use at both ends. I'm pretty sure you can just match your current nest wiring connection points on the T6 (and connect both ends of the C wire) and I think you should be good!
The other wiring (AC unit and pump) should be unaffected by switching out the stat using the same overall 1-for-1 wiring, but I'd be curious to hear if any T6 owners may be able to share any inside info.
Oh one more thing - disconnect power to the furnace while you're swapping / connecting wires (either at the stat or at the control board)... If you leave power on, it's easy to blow a fuse on the furnace board - not the end of the world, but 100% preventable by killing power to the furnace first.
Thanks! I'll pull the mount for the Nest tomorrow and confirm all the wiring is back there...the Nest was installed by the team that put in my solar (Tesla, Solar City at the time) so presumably they were also informed enough to be (not too) dangerous.
Ah yes, I learned this the hard way at my Mom's house when I replaced a thermostat and managed to blow something on the furnace somehow. Lost some points w/my Mom that day... Thanks for the reminder...
Ha, yes, back when I didn't know any better, I got lucky with not frying anything, but not worth the chance. It's all super low-voltage, so it's not going to hurt you, but futzing around with those darn fuses can be maddening when the job should otherwise already be done!
And I bet your pump only runs with the Air Conditioner (not with heat), so that's why just the Y wires involved - that would make sense. I have a high-efficiency gas furnace, so whether it's doing heat or cool, there's always water goin' into my trusty lil' pump!
Yeah, there's no need to wire a pump back to the control board, but if wired that way, it'll shut the furnace and/or AC off when it senses an overfill (plugged pump or condensate line) -- that way, the furnace/AC won't keep pumping more out water out as it cools or heats
In reality though, this isn't a huge amount of water (not like a pipe burst), but if an overflow goes unchecked over the course of a 2-week vacation, that could still suck.
Depending on your system & personal preferences, it can be wired to just shutdown AC or both Heat/AC. I have mine wired to shut down in either case, but my system will immediately send me a text/app/email alert of the shutdown.
I've never had it happen, but I'm pretty anal about keeping my pump and condensate line clean.
That is exactly what happened to us - we were on vacation, I had forgotten to turn off HVAC, and we had the unfortunate combination of a run of very hot weather and an old pump that 1) Couldn't keep up and 2) Was evidently not connected properly (installed by previous owner) to turn things off. HVAC just kept humming away churning out water. We arrived home to eight feet of ruined wood floor in the hallway outside the HVAC closet. This was well before my smarthome days, so no sensors/warnings, etc.
We replaced the pump and eventually the previous furnace as well, and I have a leak sensor in place in the pump overflow tray, and text and voice alerts, etc. This whole conversation reminds me that I forgot to have the HVAC guys who did the work on my remodel re-confirm for me that the pump was wired up correctly by the guys who did the pump replacement. Rats...
the pumps also gunk up and fail regularly.. recommend putting bleach in the pump twice a year to try to clean out the gunk.. even with that after 4-5 years you may consider replacing.
i keep two apares also on hand for when they innevitably fail.. i have a 2nd that is meatal that needs to be capable of handing 200+ water temps when the steam humidifier empties.
Just as a note, the T6 Pro can be battery powered. I’m running one at my house off battery with only a two wire steam boiler. No separate constant power wire needed. I’m certainly no HVAC expert either, but seems like it should work fine with your setup as well.
Yeah, I've had my T6 hanging on the wall on a nail above the Nest tstat for months, running it off batteries, gave my wife a chance to see the UI and compare to Nest, and she prefers the T6 UI, so that was a success. I am getting tired of replacing my smart home batteries in general, so thinking it would be good long-term to have one less device to worry about.
Saw that, but if I have the blue at both ends looks like it should be simple to connect that between the tstat and the furnace panel...(famous last words.)
