The short answer
A Google Nest works on most Lennox systems in Northern Virginia. A regular Lennox gas furnace, air conditioner or heat pump runs fine on a Nest once a C wire gives the thermostat steady power. The exception is a Lennox communicating system, the iComfort kind that talks to the equipment over data wires. Lennox’s own install guide says a communicating Lennox needs a Lennox communicating thermostat, and Google says proprietary systems aren’t compatible with a Nest. So on a communicating Lennox, keep the Lennox thermostat. On a regular Lennox, the same guide says other thermostats work.
Which Lennox do you have?
Turn the system off at the thermostat, pull it off the wall plate, and look at where the wires land. Take a photo before you unhook anything.
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| What you see | What you have | Will a Nest run it? |
|---|---|---|
| Five to eight wires on letters like R, W, Y, G, C and O | A regular 24 volt Lennox | Yes, with a C wire |
| Four wires, two of them on terminals marked I+ and I- | A Lennox iComfort communicating system | No. Keep a Lennox communicating thermostat |
| A Lennox iComfort E30 on the wall | Lennox’s smart thermostat for regular systems | Yes. The system behind it is a regular one |
| Letters, but no C and no spare wire in the bundle | A regular Lennox that will run a Nest short on power | Yes, once a C wire is run |
Then check the outdoor unit’s label. Lennox’s variable capacity models, like the XC25 and XP25, usually run on an iComfort communicating thermostat, so treat one as communicating until a tech checks the wiring.
Nest on a regular Lennox: the good and the catch
The good: the Nest Learning Thermostat learns when you’re home and builds the schedule for you. On a heat pump, its Heat Pump Balance setting decides how much to lean on the backup heat strips.
The catch is power. A lot of Lennox furnaces in older Northern Virginia houses were wired with a three or four wire bundle and no C wire, because the old thermostat ran on batteries. A Nest wants steady power, and without a C wire it borrows power through the heating and cooling wires. These are the signs Google lists:
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| What you notice | What’s going on | What fixes it |
|---|---|---|
| A low battery warning, a dark screen, or Wi-Fi dropping | Not enough power without a C wire | Connect a spare wire as C at both ends |
| Delayed or Starts in, again and again | The Nest is waiting on power before it runs the system | The same C wire. Once it has power, the waits stop |
| Clicking, the system cycling on its own, or the fan running nonstop | The Nest is pulling power through the heat or cool wire | A C wire, then set the fan to Auto |
| E1, E297, N260 or N261 | Google’s codes for a missing or weak C wire | A spare wire, Google’s Nest Power Connector, or a new wire pulled |
If there’s no spare wire in the wall, we pull a new one or add Google’s Nest Power Connector at the furnace.
Nest codes on a Lennox, and what’s usually behind them
The Nest code tells you which wire lost power. Every code is in our Nest error code guide.
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| Nest code | Google says | On a Lennox, usually |
|---|---|---|
| E2, E22, E72 | No power wires, Rc or Rh required | Power is off at the furnace or air handler, or the R wire came loose |
| E4, E24, E74 | No power to Rh | The furnace switch or breaker is off, the blower door isn’t seated, a fuse on the board blew, or the condensate float switch tripped |
| E5, E25, E75 | No heating or cooling detected | W1 or Y1 isn’t connected, or a wire broke in the wall |
| E9, E29, E79 | No power to C | The C wire isn’t landed on the furnace board’s C terminal, or it’s broken in the wall |
| E52 to E58 | Overcurrent on HVAC equipment | A shorted wire or a failing part. Stop resetting it. More in the Nest overcurrent error |
Before you reset anything, look at the furnace. Newer Lennox furnaces show a code on a small readout on the control board, and older ones blink a light. Write it down first, because cutting the power can clear it. Our Lennox error code guide reads them, and Lennox thermostat not working covers the Lennox thermostats themselves.
Heat pump trouble that comes from the setup
- Heat blows cold and the AC blows warm. The reversing valve setting is backwards. Lennox heat pumps run the reversing valve on O, powered in cooling, and a Nest starts on O. If yours is backwards, check the wire first, then the setting in the Google Home app under Settings, Thermostat, Heat pump.
- The heat strips run all the time, or never. The backup heat wire isn’t where the Nest expects it, or Heat Pump Balance is set to save the most and the house can’t keep up on a cold night. See aux heat vs emergency heat.
- Dual fuel, a heat pump with a gas furnace as backup. Check Google’s compatibility checker first.
Nest, Lennox, Honeywell or ecobee on a Lennox
Is Google Nest the best thermostat? On a Lennox, it depends on which Lennox.
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| Thermostat | Runs a communicating Lennox? | Runs a regular Lennox? | Pick it if |
|---|---|---|---|
| Google Nest Learning Thermostat | No | Yes, with a C wire | You want it to learn your schedule and you use Google Home |
| Lennox iComfort communicating thermostat | Yes, it’s the one Lennox calls for | Made for Lennox | You have an iComfort communicating system |
| Honeywell Home smart thermostat | No | Yes | You want room sensors or lots of models to pick from |
| ecobee | No | Yes, with a C wire or its power adapter | You want room sensors and Alexa or Apple Home. We install it for a flat price |
What we’d put on your wall
- A communicating iComfort Lennox: keep a Lennox communicating thermostat. If it’s failing or showing Service Urgent, the fix is the Lennox control or the system behind it, not a Nest.
- A regular Lennox furnace and AC: a Nest if you live in Google Home, an ecobee or a Honeywell Home if one bedroom always runs cold. Have a C wire run either way.
- A Lennox heat pump: a Nest Learning Thermostat or an ecobee, with the backup heat wired right and the reversing valve checked on the first cold night.
- Replacing the system soon: wait on the thermostat. A communicating system comes with its own. Shopping now? See Lennox vs Trane.
The system we put in first
Built to take a beating. Put in by our crew.
Heat lamps, snow and rain on one outdoor unit: that’s Trane’s own film. We’re a Trane Comfort Specialist, on Trane’s own dealer locator, and when you pick a Trane, our crew puts it in.
Films: Trane’s own.
When to call us
Call when a Nest code keeps coming back after a reset, when the furnace readout shows a code, or when the house won’t hold temperature. We work on Lennox furnaces, ACs, heat pumps and iComfort systems across Northern Virginia, and we read the furnace code and the thermostat wiring on the same visit. A repair visit starts with a flat $99 diagnostic, and you get the price of the fix before we start.
Want the smart thermostat done for you? Our ecobee install is a flat $549 for the thermostat and the install: wired, mounted and set up on your phone before we leave. Heading into winter, our heating check is $67 per system, through December 31: furnace, heat pump or boiler.
Have a different brand?
- Google Nest on a Trane system
- Google Nest on a Carrier system
- Google Nest on a Rheem or Ruud system
- Google Nest on a Goodman, Amana or Daikin system
- Google Nest on a Bryant system
Book it
Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook. Virginia Class A license 2705192276. Book a visit online or call (703) 997-9757. Book from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit.
Questions people ask
Does Google Nest work with Lennox?
Yes on regular 24 volt Lennox furnaces, air conditioners and heat pumps once there’s a C wire. Not on a Lennox iComfort communicating system, where Lennox calls for a Lennox communicating thermostat.
Can I replace my Lennox iComfort thermostat with a Nest?
If the wires land on I+ and I-, no: that’s a communicating system, and Lennox says it needs a Lennox communicating thermostat. Replace a failing one with another Lennox control. If the wires are on letters like R, W, Y, G and C, yes.
How do I know if my Lennox system is communicating?
Pull the thermostat off the wall. Four wires with two on terminals marked I+ and I- means communicating. An iComfort or variable capacity label on the outdoor unit points the same way.
Is a Lennox thermostat better than a Nest?
On a communicating Lennox, yes, because it’s the thermostat Lennox calls for. On a regular Lennox, a Nest, ecobee or Honeywell Home all work, so pick by the features you’ll use.
Why does my Nest say no power to Rh on my Lennox?
Usually the furnace switch or breaker is off, the blower door isn’t seated, a fuse on the board blew, or a float switch tripped. If those check out, call a tech.
