Explain how nest works with single stage Heatpump and two stages of electric heat.

[NestUser2025]

Questions : given a Lennox Merit  single stage heat pump with an inside furnace equipped with  2 stages of electric strip heat. How do I wire, connect to Nest 3rd generation, and configure the nest.

What I want:

Outside temp permitting, assume it is getting progressively cold outside

Heatpump heat is primary

Heatpump heat with stage 1 heat assist

Heatpump heat with stage 1 heat and stage 2 assist

Goes Sub zero and Heatpump is locked out

Stage 1 heat primary

Stage 1 primary and stage 2 heat assist

Factoring the Heatpump, furnace, thermostat I have these terminals.

R.

G.

C.

E.

W2.

W1.

O.

Y.

How do I connect and configured these to my NEST for maximum economy, balance or comfort?  Do believe the nest is aware of the outside temperature from the internet/wifi.

When nest display is orange it is heating from what sources?

when Nest display is Orange n displays aux heat is heating from what sources?

When Orange n displays emergency heat is heating from what sources?

personally I believe it is in the words. Believe the heat pump is augmented by aux heat w1 and or w2. The aux heat assists, vs replaces the heat pump, unless licked out. This should be helpful. Do know any of the above needs the pro setup and dual fuel mode.  

ty

[CoolingWizard · Accepted solution]

@NestUser2025 

First of all you do not have a Duel Fuel set up. The Heat Pump is Electric and the Heat Strips are Electric.  The heat strips are less efficient at converting kW of energy into BTUs of heat as compared to the Heat Pump. In colder climate areas the need for Auxiliary Heat and Emergency Heat arise.  With earlier Heat Pump technology there is a point where the heat pump might not be able to produce enough heat given the outdoor temperature and the home’s construction.  That is if the house is very drafty the cold air penetrates the home faster than the heat pump can remove it.  This is where Auxiliary heat comes in.  A thermostat can be designed to detect this interior temperature falling while the heat pump is running.  In this case the thermostat can activate the Auxiliary Heat to provide a boost of BTUs of heat.  The auxiliary heat strips can be 5kW up to 30kW. The 30 kW size is two 15kW kits.  Despite being two heat kits, this is not 2-stages of heat. Heat Strips are called resistive heat and consume lots of electricity when they first turn on.  Therefore there are components called sequencers that control the turning on of duel heat kits.  When you see Emergency Heat, this is the same heat strips only Emergency Heat can be activated by the homeowner using the thermostat.   Auxiliary Heat can only be activated by the Thermostat or by the Heat Pump during defrosting.  
There is not a “balance” point when electric heat strips are more energy inefficient than a heat pump.  And,  modern heat pump the technology has advanced to a point where the heat pump is effective and efficient to minus 23°F.  Again, the house and how well it is sealed from the outdoor cold air is important.  
Auxiliary heat is wired to W2/AUX on a heat pump knowledgeable thermostat.  Your typical heat pump thermostat wiring is as follows:

Rc 24VAC Power in from the HVAC system

Y and Y1 are the Compressor Control.  
Y2 is Stage 2 Compressor Control.

G is the Blower Fan control

OB is the Heat Pump Reversing Valve.  This switches the heat pump from cooling to heating. 
W2/AUX this is Auxiliary heat control. 
C 24VAC Power Common.  
E is Emergency Heat

Your Lennox control board cannot deal with the W1 and a heat pump.  It treats W1 as stage 1 gas heat and you do not have gas heat. Remove the jumper between W1 and W2 at the air handler.  If you have a wire for emergency Heat, land that wire on W2/AUX in the air handler.

Can you get me the model number of your Lennox Air Handler?

AC Cooling Wizard

[CoolingWizard · Accepted solution]

@NestUser2025 

Your Google Nest Learning Thermostat should have W2/Aux wire attached to W1 in the air handler. There should no jumper in the air handler between W1 and W2. You should have a wire on * on the Nest Thermostat and that will be wired to the Emergency Heat relay in the air handler. It is possible you might not have the K22 Emergency Heat Relay installed. Just wire the * to W2 on the air handler.  On the Google nest you will define the * Terminal as emergency heat. 

AC Cooling Wizard

[NestUser2025]

cooling works; it’s the heat that needs clarification.

furnace > nest 3rd generation

R. >> Rc 24v power

G. >> G fan

C. >> C 24v common

E.  >> E configured as emergency heat

W2.  >> ???

W1.  >> ???

O. >> Ob Heatpump

Y.  >> Y1 heat/cool

And configured how? Seems to need pro setup and configured for dual fuel. But a connection to Nest W1 makes it so advanced Heatpump features are not offered. Hence I jumpered w1/w2 at the furnace and wired to nest w2. Everything is working, but now I only have a single stage of assistance heat. I want two stages of Heatpump assisting heat, as Lennox intended. Heatpump, Heatpump plus w1  or Heatpump plus (w1 and w2. )   But can’t find the options to make it work AND have the option of heatpump economy, balance, or comfort. Ty

[CoolingWizard · Accepted solution]

@NestUser2025 

First of all you do not have a Duel Fuel set up. The Heat Pump is Electric and the Heat Strips are Electric.  The heat strips are less efficient at converting kW of energy into BTUs of heat as compared to the Heat Pump. In colder climate areas the need for Auxiliary Heat and Emergency Heat arise.  With earlier Heat Pump technology there is a point where the heat pump might not be able to produce enough heat given the outdoor temperature and the home’s construction.  That is if the house is very drafty the cold air penetrates the home faster than the heat pump can remove it.  This is where Auxiliary heat comes in.  A thermostat can be designed to detect this interior temperature falling while the heat pump is running.  In this case the thermostat can activate the Auxiliary Heat to provide a boost of BTUs of heat.  The auxiliary heat strips can be 5kW up to 30kW. The 30 kW size is two 15kW kits.  Despite being two heat kits, this is not 2-stages of heat. Heat Strips are called resistive heat and consume lots of electricity when they first turn on.  Therefore there are components called sequencers that control the turning on of duel heat kits.  When you see Emergency Heat, this is the same heat strips only Emergency Heat can be activated by the homeowner using the thermostat.   Auxiliary Heat can only be activated by the Thermostat or by the Heat Pump during defrosting.  
There is not a “balance” point when electric heat strips are more energy inefficient than a heat pump.  And,  modern heat pump the technology has advanced to a point where the heat pump is effective and efficient to minus 23°F.  Again, the house and how well it is sealed from the outdoor cold air is important.  
Auxiliary heat is wired to W2/AUX on a heat pump knowledgeable thermostat.  Your typical heat pump thermostat wiring is as follows:

Rc 24VAC Power in from the HVAC system

Y and Y1 are the Compressor Control.  
Y2 is Stage 2 Compressor Control.

G is the Blower Fan control

OB is the Heat Pump Reversing Valve.  This switches the heat pump from cooling to heating. 
W2/AUX this is Auxiliary heat control. 
C 24VAC Power Common.  
E is Emergency Heat

Your Lennox control board cannot deal with the W1 and a heat pump.  It treats W1 as stage 1 gas heat and you do not have gas heat. Remove the jumper between W1 and W2 at the air handler.  If you have a wire for emergency Heat, land that wire on W2/AUX in the air handler.

Can you get me the model number of your Lennox Air Handler?

AC Cooling Wizard

[NestUser2025]

Cooling Wizard - solid content. I will get you the Lennox  merit details shortly, got to find them

system was installed new in April and was believe working until it got really cold. 

At zero outside temperature, the house would only heat to 50 degrees

furnace to Nest

W1 >> W1

( no W2 >> W2). 

The Lennox hvac said my second bank of heat was not enabled. He jumpered w2/w1/E and now all banks come alive. Do understand there are sequencers driving the heat. Which I fear is not working properly, but now I do have heat)

this is the Lennox diagram with the air handler: has 4 banks of heat: each 5kw for 20kw of heat strips. Do know electric heat is expensive, hence getting it right. With sequencers, do understand why it would be single stage. 
and while I agree that an electric heat pump and electric heat strips share one fuel - electricity - was only able to bring up advanced heat pump options when dual fuel was selected

 

 

[NestUser2025]

the Lennox wiring diagram is specific to a heat pump configuration. You’re saying unjumper w1 and w2 at the furnace.  Connect (jumper?) W2 /E at the furnace???

furnace >> thermostat

W1.  To. no connection to thetmostat

w2  to w2/aux

E not connected to thermostat?

 

 

model of my air handler: 

lennx cba25uh with 20kw of electric strip heat. 

here is a link to the manual and full specs 

[CoolingWizard]

@NestUser2025 

How do I connect and configured these to my NEST for maximum economy, balance or comfort?  Do believe the nest is aware of the outside temperature from the internet/wifi.

>>The Nest Learning Thermostats use WiFi to obtain outdoor temperature data.

When nest display is orange it is heating from what sources?

>>When the Nest display is Orange it is in heating mode and heating is Active

when Nest display is Orange n displays aux heat is heating from what sources?
>>The primary heat, in your case Heat Pump.

When Orange n displays emergency heat is heating from what sources?

>> Emergency Heat has to be manually activated by the homeowner. If your heat pump fails and you need some heat, emergency heat can be activated while you wait for the repair man to show up.

personally I believe it is in the words. Believe the heat pump is augmented by aux heat w1 and or w2. The aux heat assists, vs replaces the heat pump, unless licked out. This should be helpful. Do know any of the above needs the pro setup and dual fuel mode.  

>>The heat pump is not locked out ever.  The heat pump might be assisted by auxiliary heat in extreme cold. There is no need for ProSetup for your system as you do not have a duel fuel system. 

AC Cooling Wizard

[NestUser2025]

You absolutely know more about hvac than I do. Thank you for your information and patience. Fully understand the Heatpump is more efficient. Absolutely

But find part of your reply confusing to me. Orange and orange aux heat appear to be the same, but know that’s not true. 

>>When the Nest display is Orange it is in heating mode and heating is Active

(Thinking: in our discussion context,  the heat pump alone is providing heat)

when Nest display is Orange n displays aux heat is heating from what sources?
>>The primary heat, in your case Heat Pump.

( believe this is incomplete ( I apologize ) The heat pump is providing primary heat and being assisted with aux heat from the heat strips. Those heating strips are in the furnace and based in demand, will sequence between one to many strips of heat)

Emergency heat - thank you, manually called for, not part of the automation. 

W1, and W2. When I researched this, the internet said as beliw calling them stages. My furnace has four banks of heat, 4x 5kw. When only W1 was connected the banks were running at 50% of amp capacity. Jumpering W1 and W2 game me 100% the rated amps, although as you said, not right away, they were sequenced on. 

Question: you have the furnace wiring detail from Lennox. Given W1 and W2 on the furnace where do these connect on my nest?  Intuition says w1 to w1 and w2 to w2. And E to star, but this did not enable any Heatpump options which do not present if a wire is in W1 ( I could be wrong)

internet calls W1 and W2 as two stages of heat. Do understand they each likely have their own sequencers on board

”In an electric furnace, "W1" refers to the first stage of heating, while "W2" refers to the second stage of heating, meaning that when a thermostat is set to use "W2," it will activate a higher heating capacity to warm the space faster than using "W1" alone; essentially, W1 is the primary heat setting and W2 is the auxiliary or "boost" heat setting. 

Key points about W1 and W2:

• Multiple heating stages:

  Some furnaces are designed with multiple heating stages, allowing for more precise temperature control. 
• Thermostat connection:

  On a thermostat, the "W" terminal is typically used for heating, and if a system has multiple stages, you would connect the "W1" wire for the first stage and the "W2" wire for the second stage. ” google reply 

And in my nest as configured as dual fuel (yes am aware just the ne fuel - electric) 

nest app on my phone, as configured, offers heat pump balance options. In part because no W1?  And yes, I have it configured for single furl

Odd, can’t upload a picture of the heat pump balance features. Sorry. 

[NestUser2025]

Just need to know where the wires connect, if they connect at all. 

R. >> Rc 24v power

G. >> G fan

C. >> C 24v common

E.  >> ???

W2.  >> ???

W1.  >> ???

O. >> Ob Heatpump

Y.  >> Y1 heat/cool

this is an image of the link to the Lennox manual including the wiring they suggest. 

 

[NestUser2025]

The manual is here

Lennox cba25uh air handler (furnace) manual with heat options and suggested detailed wiring  with a Heatpump. ( not nest aware). 

https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/corp1705a.pdf tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/corp1705a.pdf

[NestUser2025]

Cooling Wizard, found the model details. 

Lennox Merit® Series
CBA25UH Air Handler Units with 20KW electric heat, 4 banks of 5kw

M/N CBA25UH-060-230 - 03

Plus heat: ECBA25-20CB-P

Outside Lennox Heat pump
M/N. ML17XP1-048-230A01

[CoolingWizard · Accepted solution]

@NestUser2025 

Your Google Nest Learning Thermostat should have W2/Aux wire attached to W1 in the air handler. There should no jumper in the air handler between W1 and W2. You should have a wire on * on the Nest Thermostat and that will be wired to the Emergency Heat relay in the air handler. It is possible you might not have the K22 Emergency Heat Relay installed. Just wire the * to W2 on the air handler.  On the Google nest you will define the * Terminal as emergency heat. 

AC Cooling Wizard

[NestUser2025]

Cooling wizard, (fingers crossed) did as you directed. It’s 43f outside, so can’t confirm if it’s working fully.  One false step, contractors were doing siding and unplugged the heat pump, so that doesn’t count as not working. We’re changing only two wires. And any jumper between w1  and w2 at the air handler removed. 

furnace > nest 3rd generation 

w1  >> nest w2/aux

W2 >> * configured as emergency heat 

do not believe there is any outside relay for temp, likely not necessary with nest getting outside temperature from the internet. 

Based on your advice (ty)

R. >> Rc 24v power

G. >> G fan

C. >> C 24v common

W2.  >> * emergency heat

W1.  >> w2/aux

O. >> Ob Heatpump

Y.  >> Y1 heat/cool

 

[NestUser2025]

As my testing goes. It’s 42f outside, sun is setting. House shows 67, and I set the heat at 90, expecting to see a call for aux heat / nope. Fan is running high vs the low speed it was (no em heat, w1/w2 jumpered at the air handler). Thought the high speed and lack of calling for aux heat was odd. FYI 

 

[CoolingWizard · Accepted solution]

@NestUser2025 ,

you have to understand how you’re very particular air handler operates what they call the heating cycle call. When you do this, the thermostat has to wait for 15 minutes to ensure the system is running properly and producing some heat. If you do the way you do it the thermostat ignores the call for auxiliary heat. What you need to do is set the temperature for say 70° F and wait 15 minutes and see if the auxiliary heat kicks in. 
also anytime the outdoor unit ice is up and it’s detected by the outdoor unit. It sends a signal to the air handler to turn on the auxiliary heat while it reverses the reversing valve to steal heat from inside the house to take outside and melt the ice. Basically it’s running like an air conditioner for a few minutes.

if the system has been running for at least 30 minutes and the thermostat servers that the temperature is continuing to drop inside the house it will turn on the auxiliary heat to help boost the heat and give some help to the heat pump.

AC Cooling Wizard

[NestUser2025]

Ahah!  For some reason I had thought there was a heat element in the outside Heatpump.  That explains it.  Thank you for your patience. 

[NestUser2025]

CoolingWizard -,Just sharing - looks like everything is working with your wiring. Heatpump meeting demand and when i make a call to raise to 90F, aux heat is requested. Fully satisfied. 

furnace >> nest

w1 >> w2/aux 

W2 >> * as emergency heat

single fuel - electric 

fyi: have continuous fan enabled. And when there is a call for heat, instead of med fan (expected), it seems to go to high fan. I’ve noticed this happens after jostling the two double pole breakers after I put the cover back, if the fan jumps to high, I cycle the breakers  once or twice, and heat fan dops to med. And continues working fine.  Thought it odd, and rather that figure out why, I have elected to leave it like Jimmy said to John wick - I see your working, and will leave you be. 

Picture is evidence a call for high heat  is working as intended. This was a test, no I don’t heat the house to 90. And my configuration details for others. Full credit to the cooling wizard.  

 

 

 

 

 

[NestUser2025]

Cooling Wizard, wanted to mark the above as having answered the question - how to wire this particular Lennox Heatpump (new ihvac April 2024). Everything is working - credit to you. 
(Do have a question, but will add it elsewhere )

thank you!  The cooling wizard is awesome.