Nest wiring question

[Timster1]

Hello, I am trying to setup Nest Thermostat to replace my Honeywell thermostat. I have a heat pump with 3 zones system with Emergency heat. “No AUX heat” according to my HVAC company that installed it. The Honeywell is currently has 6 wires Y- Yellow, G- Green, C- Blue, R- Red, O/B- Brown and “aux/W2-White”.  This W2 is what throw me off because we don’t have Aux Heat. Only emergency Heat. So I’m trying to figure out could I put the white wire in the * on the nest and set it as emergency heat. TIA

[CoolingWizard · Accepted solution]

@Timster1 , the emergency heat, if you have a wire conductor available p, as in not being used, can be allocated for emergency Heat. Alternatively you can take the W2 wire and put it on the * terminal and designate it Emergency Heat.  If the HVAC contractor wired your heat pump correctly, the Defrost Control Board (DFC) in the outdoor unit should  be wired to the auxiliary heat in the air handler.  What you will loose is the ability of the Nest Thermostat to detect the heat pump loosing its heating capacity and the thermostat to activate the auxiliary heat to help. 

Although this is not an Google Nest approved approach, I have made a jumper wire from the W2 conductor wire to the * terminal.  I do this by carefully removing a small area of insulation on the W2 wire and then attach a wire there, and plug the other end into the * terminal to get an emergency heat function.  

AC Cooling Wizard

[CoolingWizard · Accepted solution]

The way Emergency Heat works is that the thermostat can activate the emergency heat when it energizes the * wire.  However, advanced systems use an advanced controller in the air handler that manages the electric heat strips.  Is there a way to get the indoor air handler model number so I can look up the capabilities.  

And, for the record, the emergency heat and the auxiliary heat are the exact same electric heat strips that are located in the air handler blower cabinet. 

When you have a heat pump, the W1 is not typically used except in Duel Fuel systems. The W2/AUX is the auxiliary heat terminal.  Emergency heat on older thermostats is the X terminal is there is no E terminal. 

AC Cooling Wizard

[CoolingWizard]

@Timster1 , Depending on your Honeywell thermostat, it can be programmed to perform different. The AUX/W2 is a such a terminal.  This terminal can  be programmed as either and Auxiliary Heat or Stage 2 Heating or Emergency Heat  In the control systems of the HVAC equipment there is not actually a separate Auxiliary Heat versus Emergency heat.  The concept of Emergency Heat is that the homeowner can activate the electric heat strips manually using the thermostat.  Now the outdoor heat pump unit can automatically turn on the same electrical heat strips when the outdoor unit goes into Defrost mode.  Just rest assured that if you want to have Emergency Heat capability with your Nest Thermostat, you will need to connect the white wire to the * terminal.   Now let us talk a bit more about Auxiliary Heat function. 

When a heat pump is in heating mode, and the outdoor temperature get close to zero degrees, the efficiency falls off and if your house is not well sealed or insulated, the Auxiliary Heat can be activated by the thermostat to give a heating boost.  Now then, when the heat pump outdoor unit is heating, outdoor coil will tend to ice up.  The outdoor unit Defrost Control board (DFC) detects the ice build up and takes over the control of the system.  It sends a signal to the indoor air handler to activate the auxiliary heat and slow the blower down to low.  At the same time it switches the reversing valve back cooling mode in order to extract the heat inside the house to melt the ice.  Once the ice is melted, the DFC terminates the defrost cycle.  

AC Cooling Wizard

AC Cooling Wizard

[Timster1]

 

Honeywell wires in current system. It does say in setting that I have 2 stage heating. This is the wire diagram that nest show me to wire when I put in the wires

so can I still activate emergency heat on demand?  Thanks

[CoolingWizard · Accepted solution]

@Timster1 , the emergency heat, if you have a wire conductor available p, as in not being used, can be allocated for emergency Heat. Alternatively you can take the W2 wire and put it on the * terminal and designate it Emergency Heat.  If the HVAC contractor wired your heat pump correctly, the Defrost Control Board (DFC) in the outdoor unit should  be wired to the auxiliary heat in the air handler.  What you will loose is the ability of the Nest Thermostat to detect the heat pump loosing its heating capacity and the thermostat to activate the auxiliary heat to help. 

Although this is not an Google Nest approved approach, I have made a jumper wire from the W2 conductor wire to the * terminal.  I do this by carefully removing a small area of insulation on the W2 wire and then attach a wire there, and plug the other end into the * terminal to get an emergency heat function.  

AC Cooling Wizard

[Timster1]

I attached a pic of what it wanted me to put the wires on the nest based on the original wiring from Honeywell . the HVAC company told us that we don't have auxiliary heat. Just 2 stage heating and emergency heat. I tried wiring it to w2/aux on the nest. Test the aux heat it just blows air. That's why I wanted know if I could put the white wire in w1, or the * on the nest and have emergency heat on demand if I need it.  

[CoolingWizard · Accepted solution]

The way Emergency Heat works is that the thermostat can activate the emergency heat when it energizes the * wire.  However, advanced systems use an advanced controller in the air handler that manages the electric heat strips.  Is there a way to get the indoor air handler model number so I can look up the capabilities.  

And, for the record, the emergency heat and the auxiliary heat are the exact same electric heat strips that are located in the air handler blower cabinet. 

When you have a heat pump, the W1 is not typically used except in Duel Fuel systems. The W2/AUX is the auxiliary heat terminal.  Emergency heat on older thermostats is the X terminal is there is no E terminal. 

AC Cooling Wizard

[Timster1]

 just checked the air handler and the zone pad. It has the white wire going w1/e so where should I hook it up on the nest? W1 or * for emergency heat. Thanks

[CoolingWizard]

See where the installer wrote 60AMP 15kW on the label. You have 15kilo Watt of electric heat strips installed in your air handler.  Your HZ322 zone controller does not have a separate Emergency and Auxiliary Heat connection.  Do you know if your thermostat cable has 7 conductor wires and only 6 being used? Sometimes there is 7th wire and it might be tucked inside the wall.  If there is a 7th conductor wire, we can wire it to * on the Nest and configure it for Emergency Heat.  And then on HZ322 we add that wire to W1/AUX with the white wire. 

AC Cooling Wizard

[Timster1]

 Thanks for the quick reply sadly it's only 6 wires. So I'm just wondering if I could jaut put that white wire on the * of the nest and the system will still work?

[CoolingWizard]

@Timster1 , of you choose to put it on the * to enable emergency heat there would be no real problem. 

AC Cooling Wizard

AC Cooling Wizard

[Timster1]

Thank you! One more question can I still put it on w1 on nest and still have emergency heat?

[CoolingWizard · Accepted solution]

@Timster1 , your old thermostat did not have Emergency Heat,  however,  there is a work around since your HZ322 does not specifically have a separate emergency heat terminal. What I am going to describe is not endorsed nor approved by Google Nest.  

When attaching wires to the Nest Thermostat, the thermostat cable conductor wires should be 18AWG solid conductor.  Now, then you cannot insert two wires into a Nest backplate terminal. What you can do is make the a connection between the W1 wire and insert into the * terminal.  Wrap the E wire around the W1 bare copper and just insert the other end into the *. 

AC Cooling Wizard

[Timster1]

 These are the only setting on the thermostat Honeywell. They have the white wire under w2/aux but on the panel the white wire to the equip is w1/E which means I don't have aux heat just emergency heat setting. As long as there won't be any issue if I put the wire in the * and use it as emergency heat. I will wire the nest up. Thanks

[CoolingWizard]

The thermostat you have has an Emergency heat terminal and it is labeled E and there is no wire attached to it. Since the electric heat strips are the used for both Auxiliary and Emergency heating, anytime the HZ322 sense a call for heat on W1/E, the electric heat strips will be energized.  

When the outdoor unit ices up when in heating mode, the defrost control board will activate the W1 to provide auxiliary heat while the heat pump is in defrost cycle.  Also, when you have an intelligent thermostat like the Nest Learning Thermostat , the thermostat can detect on very cold nights when the heat pump cannot keep up. At that time the thermostat will activate the Auxiliary heat to boost the heating.  

Now then, if a heat outdoor should fail and require repair, the homeowner can activate the Emergency heat using the thermostat. By doing this you will still have heat while you wait for the repairman to arrive. Normally with a heat pump and both auxiliary and emergency heat, the Emergency Heat is wired to W1/E and the auxiliary heat is wired to the W2. 
AC Cooling Wizard

[Timster1]

Thank you for that. But I do not have a wire that is wired to w2. Which means I don't have aux heat. So it's okay to wire it to w1 or * since I have to active emergency heat on demand. 

[CoolingWizard]

@Timster1 , this determines by your own self snd what you want to do. In fact, the outdoor heat pump is wired to the W1/E terminal of your 322.  And likewise, all of your thermostats are also wired to the W1/E. You can consider additional possibility as well. If you will put in nest power adapters for each thermostat, you will free up a wire that can be used to give you emergency heat and auxiliary heat. 

AC Cooling Wizard