Lennox furnace with ecobee3 (or nest)

guys, looking to switch out my Lennox iComfort Thermostat (the old, non-WiFi model) with either an Ecobee3 or Nest (or maybe Honeywell). Current wiring is an R, C, and an i+ and i-. Does anybody know what these might be equivalent to? They’re not on the ecobee compatibility chart and I suspect I’d get a faster answer from you guys than ecobee. Forgot to mention it also a Lennox furnace and Central AC unit.

you should ask Lennox or research for an adapter to convert to standard wiring terminal strip (typically R,C,O,W,Y,and others). Yours sounds like a “communicating/intelligent” proprietary thermostat wiring interface.

Frankly I would not expect you to be able to switch it out.


Thanks for the feedback. I’ve surmised so far that the i+ and i- lines are definitely comm lines and I suspect, as you mentioned, it’s something proprietary. I’ve got an email into Ecobee for suggestions but no response yet.

I’ve not had much like finding an adapter but I’m still hunting. I’ll put a call into Lennox but I don’t suspect they want to tell me how to use a competitor’s device when they could sell me their own. But maybe.

I need to look into the thermostat you attached - could be a viable alternative to Ecobee3. The Lennox’s latest offering, the iComfort S30, looks nice but is hard to find unless bought from an authorized dealer - it’s also pretty expensive.

Per the manual its the data information connection. Hit up Nest support they are pretty helpful, even if you don’t choose Nest it may point you in the right direction.

I believe iComfort is a proprietary Lennox system. You may need to have an HVAC pro rewire it using the traditional points on you units.

Alright, so I did more digging and determined, based on some input from some HVAC pros, that the system I have would actually lose efficiency if I switched to a Nest/Ecobee/other non-Lennox Tstat. My furnace is an SLP98UHV which I guess is designed to communicate with my Lennox Tstat.

I suppose the HVAC guys could just be trying to sell the more expensive Lennox products, but the answer makes sense.

thanks for the followup.

Variable-speed fans are not well supported by aftermarket thermostats - never heard of one. You could probably pick a single-speed to operate and cycle it with a Nest or Ecobee3.

Variable is nice for lower noise and higher efficiency, but it’s more complicated and they get you locked in to their system.

They are not. An SLP will modulate from 40 to 100% of it actual nameplate BTU. Any stat other than the Lennox control will result in your furnace becoming a 3 stage turd. No manufacturer that I am aware of has open sourced their communication between the control and the furnace and none probably ever will. Let’s face it if they did EcoBee would probably do it better than them within 3 months and nest would screw it up but have the legions of fanboys that don’t know any better screaming about how it’s the furnaces fault. Either way the manufacturers lose money.

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Hello there,
Did you advanced with your problem?
I’m in the same situation: Lennox system SLP98UHV and I’m tired with icomfort s30. I miss my Ecobee… or my Nest (previous thermostats)

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I agree with you 100%… I have an S30 iComfort and miss my Ecobee… I paid a lot for that S30 and it was a step down on the feature set. I was told when I purchased the SLP98v furnace and XC25 a/c that the Ecobee would be unable to control the units properly. I also have the PureAir u/v air cleaner which the S30 controls… Still holding out hope that it becomes a supported option at some point.

This is normally controlled by applying 120V AC power to it from the air handler. It’s not controlled by thermostat. Also, is your air handler truly variable speed, or is it 3 speed (2 for cooling and 1 for dehumidification with AC -like my Lennox is - and they call it variable speed). In time, I went from iComfort to Heneywell Prestige and now Ecobee and it controls my system perfectly.
The issue you might have is that if your installer used i+ and i-, then you don’t have enough wires. I have 6 wires for AC control - R, C, G, Y1, Y2, D. Heating is another wire - W - but that’s separated.
Take a look at wiring in the documentation the installer left for you (air handler is important) ad see what’s required option wise. Model number of equipment is important, but also manufacturing year as Lennox maintains same model number but wiring changes.


I know this is an older thread but I just bought into the same problem. Lennox is telling me I can’t use my Ecobee and even if I could it wouldn’t support the advanced variable speed features of my new AC and furnace. And of course they don’t support SmartThings and not even IFTTT.

So… I am taking matters into my own hands and writing a DTH. I’m starting by sniffing their web app using fiddler: https://www.telerik.com/fiddler

I know they have an API because they support Alexa so this is possible. It will just take time. So far I have all the web calls and auth flows decoded. Stay tuned as I make progress.


Thanks all for this super helpful discussion. I’m going through the same issue with my iComfort (piece of crap) and dreaming of switching to Nest. Guess I have to keep dreaming for now. :cry:

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At least they now also have iOS HomeKit integration. I am looking into whether that can be a bridge to ST using HomeBridge from this forum.

I know that I’m late to the party here, but for posterity’s sake, I’d like to clear up a few things. You can use a Nest or Ecobee with the Lennox SLP98UHV. I got a quote from my HVAC professional for something like $1200 to install, which I thought was ludicrous. Faced with that steep price tag, I did something even crazier and cracked open the manual.

The SLP is designed to work just fine with single-stage or two-stage thermostats. It has a microcontroller inside the furnace that modulates the heat output based on how often and how long the different stages have been called for, somewhere form 35% to 100% of the nameplate BTUs, modulating the fan to match. DIP switches on the furnace control board have to be properly configured for this, but it’s all laid out very clearly in the installation manual.

Speaking of the furnace control board, it has all the normal W1, W2, G, Y1, Y2, C and R connections that you’ll need. If your installer put in a communicating thermostat, then you’ll need to pull a new cable through your walls. But, everything is clearly labeled and as long as you’re comfortable popping the side off your furnace (and you’re absolutely sure you’ve shut off the power to the unit at the breaker), it is a fairly straightforward, if tedious, process.

My HVAC tech also gave me a very long spiel about how the unit would be “less efficient” with a Nest. I think this is deceptive, if not dishonest. The fuel efficiency of the unit is fixed. A communicating thermostat is only “more efficient” in the sense that it has finer control of the fan and the furnace. The simple truth is that your house loses heat to the environment and it will need a certain amount of BTUs from a heating system to keep it warm. ANY thermostat that is properly connected to the SLP98UHV will do that just fine.

Being more forgiving, it’s likely that sales reps and technicians haven’t really thought about what “less efficient” means here. They’re probably just thinking that all of the stuff they’ve read in the manuals and sales brochures says that the iComfort system is “more efficient”, so that means that anything else is logically “less efficient”.

I pulled a new wire from the furnace to my thermostat. wired everything up, and I’ve got a Nest working with it just fine. It took about a week for the Nest to “learn” when it need to call for Stage 2 cooling instead of Stage 1, based on the outside temperature and the specifics of my home, but everything is working just fine now.


Thanks for this… going to work on getting my Ecobee back on the wall this weekend.

Okay - I cracked open my furnace and sure enough all the usual terminals are there. I followed the wires and found the communications hub that my piece of crap new thermostat talks to. Now I am just looking for the original wires in the wall. I have a sinking feeling my installer yanked them out. Anyway I am optimistic this will work.

By the way, I have an Lennox EL296UHV furnace. The controller board has both communicating thermostat terminals and traditional terminals. See photo. So my ecobee is going to be connected to the traditional ones.

Okay folks - got my Ecobee back and I’m super happy. The install wasn’t hard. The only tricky parts were removing the smart hub and feeding the old cable back into the furnace unit. Then I just connected it as usual but used the traditional terminals instead of the connected ones. I had to flip one dip switch on the furnace board to tell it to emulate a two stage thermostat since I didn’t have enough wires in the wall to hook up Ecobee as a true two stage. The following photos might help someone so I’m including them. They show the dip switches, the terminals, and the happy finished product

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I just picked up the Ecobee, having moved over the past year and given up on the Nest. I have the same furnace, but not sure about the wiring yet. This thread has given me confidence. Photo linked.

Google Photos

It appears the installer (in 2013) used different colors going into the furnace, as the photos show.

Google Photos

Google Photos

You mentioned a dipswitch , I assume it’s the last image top #1?

Yes the ones on the bottom left of the photo in my post. One word of warning though… this story isn’t over. I talked to my furnace guy again and he thinks this wiring won’t work for the AC when summer arrives because the AC unit only has wiring for a communicating thermostat. It works great for the furnace in heat mode. He is researching it over the winter. If we find a solution I will post it here. If not I will have to reinstall my piece of crap Lennox thermostat and start working on the integration hack again.