Wiring for Carrier 2-stage heatpump/furnace hybrid

jplee3 · Nov 10, 2022

Hi all,

We are having a new hybrid system installed (Carrier 24HCB648 and 58CUOAO80C2120) and I was under the impression that we could easily switch between gas and electric for heating at the thermostat (they are installing an Ecobee Premium).

The lead installer today is saying that in order to switch modes, he would have to physically rewire the heat pump and/or furnace each time we want to change the heating mode.

Can anyone confirm this?

EDIT: I have been talking about this with the owner and he seems to think there is a way to do it, and is going to pass it on to his senior technician to look into it more.

BNME8EZ · Nov 10, 2022

Not a Carrier dealer but that sounds like pure BS. Every heat pump system I have seen if nothing else you could set the thermostat from heat to EM heat and it would switch from heat pump to gas. Normally if wired correctly with the correct thermostat or control package it will do it automatically when the outside temperature gets too cold or it can be wired so the heat pump will run until the house drops roughly 2 degrees below setpoint and it will bring the furnace on which will run until the call for heat is satisfied at the thermostat.

Maybe the problem is the equipment, maybe it is the thermostat, but my money would be the problem is on the technician.

jplee3 · Nov 10, 2022

BNME8EZ said:
Not a Carrier dealer but that sounds like pure BS. Every heat pump system I have seen if nothing else you could set the thermostat from heat to EM heat and it would switch from heat pump to gas. Normally if wired correctly with the correct thermostat or control package it will do it automatically when the outside temperature gets too cold or it can be wired so the heat pump will run until the house drops roughly 2 degrees below setpoint and it will bring the furnace on which will run until the call for heat is satisfied at the thermostat.

Maybe the problem is the equipment, maybe it is the thermostat, but my money would be the problem is on the technician.

The way you're explaining it sounds to me like the way it should work with a hybrid setup... *shrug* If it is in fact on the tech, I'm assuming he probably hasn't really done a hybrid install or wiring for it before so he's unaware and/or doesn't realize it's possible. Hopefully he doesn't do anything that's "set in stone" as far as provisioning for this in the future (assuming it is possible and the owner just needs to send his senior guy out to make the changes)

Bazooka Joe · Nov 10, 2022

“The lead installer”

Isn’t a installer more of a person concentrating on installing ductwork, equipment, etc. etc. more or less? and the senior Tech. more a person doing lineset hookups, startup/commissioning and wiring of systems??

Someone going to do one of these on your system? Called a startup/commissioning report?

https://www.energystar.gov/sites/default/files/National HVAC Commissioning Checklist _Rev 11.pdf

Make sure to register each piece ( including indoor coil ) as manufacturers warranty decreases if system never gets registered.

If they installed AHRI matched system, chances your system can apply for any rebates your state/local utility company may offer. You don’t go by the outdoor unit rating alone to get your SEER, HSPF and EER ratings, to get those rating the indoor section would need to match to the outdoor section.

You can ask them for the AHRI number to see what those ratings are, providing they installed AHRI matched equipment. Not real world numbers but nice to know what your getting for what your paying for and certainly need a number to submit for money in your pocket rebates.

https://www.ahridirectory.org/

There is also the Federal Tax Credit on the Heat Pump side.

https://www.energystar.gov/about/federal_tax_credits/non_business_energy_property_tax_credits

jplee3 · Nov 10, 2022

Bazooka Joe said:
“The lead installer”

Isn’t a installer more of a person concentrating on installing ductwork equipment and so more or less? and the senior Tech. more a startup/commissioning of system and wiring of system??

Forgive my lack of understanding of the titles/roles. I just assumed he's the lead installer because he's the one 'in charge' as they're installing the system. The guy who came out last week to remove our unit seemed to me like the senior tech (he and the owner did a Manual J calc at our place earlier in the year). Anyway, assuming that guy is the senior tech, I'm surprised I haven't seen him at all... maybe they're trusting the installers to do everything they need to and will come back to make any final touches as necessary?

BNME8EZ · Nov 10, 2022

jplee3 said:
The way you're explaining it sounds to me like the way it should work with a hybrid setup... *shrug* If it is in fact on the tech, I'm assuming he probably hasn't really done a hybrid install or wiring for it before so he's unaware and/or doesn't realize it's possible. Hopefully he doesn't do anything that's "set in stone" as far as provisioning for this in the future (assuming it is possible and the owner just needs to send his senior guy out to make the changes)

I sell Trane equipment so I can't talk for Carrier but I can't believe there would be that much difference. In the Trane install guides for equipment and stats they have multiple diagrams to show how to wire the equipment for different applications ie furnace & A/C, heat pump, heat pump hybrid, 2 stg furnace & A/C, etc, etc, etc , many have over 20 diagrams that may come into play with the equipment so you have to pick the appropriate one. Adding an stat from a different manufacturer adds to the process but should not make it impossible. If it does then a different thermostat should be considered.

ss120396 · Nov 10, 2022

They are completely wrong. Every properly wired and configured dual fuel system will have the capability to switch to gas heat from the thermostat by default, using the "emergency heat" setting.

FlyersFan · Nov 10, 2022

The installer is wrong. That Ecobee can handle a dual fuel/hybrid heat system. It's all in the wiring and the setup of the Ecobee. I'd hold out for the senior tech or the owner (if he was once a tech) to come do the final low voltage wiring and startup. If it's not set up right it could damage the heat pump if the compressor and the gas heat are running at the same time.

jplee3 · Nov 11, 2022

FlyersFan said:
The installer is wrong. That Ecobee can handle a dual fuel/hybrid heat system. It's all in the wiring and the setup of the Ecobee. I'd hold out for the senior tech or the owner (if he was once a tech) to come do the final low voltage wiring and startup. If it's not set up right it could damage the heat pump if the compressor and the gas heat are running at the same time.

Thanks. I'll have to press them to make it right. I was looking at the wiring on it and my understanding is that there should also be an O/B wire? I don't see that connected currently. Hopefully they can make it work right. He did seem to understand the backup heat/thermostat trigger mode where the gas heat will be auxiliary secondary and only kick in if the temp drops below a certain point. My understanding was that this temp range is adjustable AND you can manually force usage of the aux heat as well if you want to. It sounds like they may need to look at the wiring again to figure it out. Is there a good reference specifically for Carrier 2-stage heatpumps + gas furnaces used with Ecobee that I can point the installer to just in case?

Bazooka Joe · Nov 11, 2022

“We are having a new hybrid system installed Carrier 24HCB648”

I don’t see a 24HCB6 Carrier two stage Heat Pump line, a 25HCB6 two stage Heat Pump yes. Unless that’s some unadvertised Contractors special?

https://www.carrier.com/residential/en/us/products/heat-pumps/

“I was looking at the wiring on it and my understanding is that there should also be an O/B wire? I don't see that connected currently.”

From 2012 wiring diagram thou.

https://www.shareddocs.com/hvac/docs/1009/Public/08/25HCB6-2W.pdf

Shows the O terminal needs to be hooked to get the Reversing Valve operation to work. Try running your Heat Pump in cool and heat mode, to see if those modes work. You can touch the larger insulated copper line in each mode for the temperature difference.

BaldLoonie · Nov 11, 2022

The Bee can easily do dual fuel as long as "electric" is the heat pump and not strip heat in addition to the gas furnace. That would be a challenge. If set up properly, when the outdoor temp drops below the setpoint, the HP should shut off and the gas fire. The stat likely would energize gas above the changeover point if the HP isn't keeping up. I don't have mine set that way.

jplee3 · Nov 11, 2022

Bazooka Joe said:
“We are having a new hybrid system installed Carrier 24HCB648”

I don’t see a 24HCB6 Carrier two stage Heat Pump line, a 25HCB6 two stage Heat Pump yes. Unless that’s some unadvertised Contractors special?

https://www.carrier.com/residential/en/us/products/heat-pumps/

“I was looking at the wiring on it and my understanding is that there should also be an O/B wire? I don't see that connected currently.”

From 2012 wiring diagram thou.

https://www.shareddocs.com/hvac/docs/1009/Public/08/25HCB6-2W.pdf

Shows the O terminal needs to be hooked to get the Reversing Valve operation to work. Try running your Heat Pump in cool and heat mode, to see if those modes work. You can touch the larger insulated copper line in each mode for the temperature difference.

Ah yes, you are correct. I actually pointed this out to him but he never updated the invoice (which is what I copied/pasted from hahaha). It the 25HCB6 - https://www.carrier.com/residential/en/us/products/heat-pumps/25hcb6/

I think the current wiring the installer did was at the heatpump and he *may* have just bypassed the heatpump heating function all together and wired this up like a standard AC/gas furnace set?

Bazooka Joe · Nov 11, 2022

Did you specifically say ( contract ) you wanted a Heat Pump Hybrid system, or a two stage straight A/C Hybrid system. Again place your heating system to run ( if it’s above the balance point ) doesn’t the system call for outdoor unit and indoor blower to run to heat your residence? if so put your hand on the larger copper line of the lineset,to confirm after systems been running 5+ minutes to stabilize, then put it in cool mode, and put your hand on the same line, it should be cool to the touch. does your A/C work OK, as typically the O terminal energizes/deenergizes the RV coil. You mention the O terminal at the thermostat or outdoor unit?? Is not hooked up, is that correct?

jplee3 · Nov 11, 2022

Bazooka Joe said:
Did you specifically say ( contract ) you wanted a Heat Pump Hybrid system, or a two stage straight A/C Hybrid system. Again place your heating system to run ( if it’s above the balance point ) doesn’t the system call for outdoor unit and heat your residence? if so put it in cool mode, does your A/C work OK, as typically the O terminal energizes/deenergizes the RV coil. You mention the O terminal at the thermostat? Is not hooked up, is that correct?

What it states is "Carrier Performance Series 16 SEER 2-speed Hybrid Heat Pump AC with Gas Furnace"

Currently, the system calls directly for gas. The reason I bought wasn't because we're in an area that gets super cold outside to where we need this system for when the heatpump *can't* run - I got it more with the intent of being able to switch between gas vs electric heat based on local gas and electric rates. Cooling works just fine too - they tested everything yesterday towards the end of the install. Not sure how helpful it would be but I can grab a screen of the wiring on Ecobee and paste it up here

Bazooka Joe · Nov 11, 2022

Sounds like you do the switching manually at the thermostat instead of having a true Hybrid system whereas the OD temperature switches from HP to Gas and vise versa while in heat setting? So if the OD temperature is say 50 degree and you have your thermostat set to heat, your gas runs? only time the outdoor unit runs is for A/C cooling?

I’m confused :Faint:

So again where is the O terminal not hooked up, at the thermostat or outdoor unit or both?

jplee3 · Nov 11, 2022

Bazooka Joe said:
Sounds like you do the switching manually at the thermostat instead of having a true Hybrid system whereas the OD temperature switches from HP to Gas and vise versa? So if the OD temperature is say 50 degree and you have your thermostat set to heat, your gas runs? only time the outdoor unit runs is for A/C cooling?

I’m confused :Faint:

So again where is the O terminal not hooked up, at the thermostat or outdoor unit or both?

Yea, only gas is running per my understanding when heat is called and the only time the outdoor unit runs is when AC cooling is called. Also I noticed for heat, it only runs in the first stage? It doesn't seem to blast heat out like our old furnace did. But maybe that's because it's "higher efficiency" and therefore shouldn't need to. Or maybe because the temp differential inside between our current/target is only a few degrees so it would likely never need to get to the point of kicking into the 2nd stage? I'm not sure...

I'm not really sure where the O terminal isn't connected. I'd have to ask the HVAC contractor... unless there's an easy way for me to find out? I can open up the furnace and take a peek. I'll post up some pics of the wiring if I can.

Looks like to check the actual wiring itself I'd have to remove more panels off the furnace, which I'll need a bit longer to do... is there anything I can check at the heatpump itself?

Bazooka Joe · Nov 11, 2022

“I was looking at the wiring on it and my understanding is that there should also be an O/B wire? I don't see that connected currently“

Your statement not mine, you clearly say you don’t see the O terminal hooked up, my question is where are you referencing this, at the thermostat?

Now you say, “I'm not really sure where the O terminal isn't connected”

So,…what type of system did you want, ( not currently have working ) a true Hybrid ( using OD temperature to switch from heat pump to gas and vise versa ) if so it’s not wired that way from here.

Shouldn’t be rocket science to figure out how to get a true Hybrid system if that’s what you want.

What happens when you put system to emergency heat mode? does the furnace run and HP never comes on , like it suppose to.

Typically all you got to do is raise your setting on the thermostat to get a higher differential to get the 2nd stage to come on for the furnace, chances the blower speed increases RPM?

Not asking you to open furnace to check O terminal as typically there is a dummy O terminal or no O hookup at a gas furnace, the outdoor unit terminal board typically has all your low voltage hookup including O. Not asking you to remove thermostat to see sub base. Again not asking you to open panels outside, unless your comfortable doing so with main power turned off.

So just call them and have their crack senior Tech. wire for Hybrid as that’s what your paying for no? A Hybrid system?

jplee3 · Nov 11, 2022

Bazooka Joe said:
“I was looking at the wiring on it and my understanding is that there should also be an O/B wire? I don't see that connected currently“

Your statement not mine, you clearly say you don’t see the O terminal hooked up, my question is where are you referencing this, at the thermostat?

Now you say, “I'm not really sure where the O terminal isn't connected”

So,…what type of system did you want, ( not currently have working ) a true Hybrid ( using OD temperature to switch from heat pump to gas and vise versa ) if so it’s not wired that way from here.

Shouldn’t be rocket science to figure out how to get a true Hybrid system if that’s what you want.

What happens when you put system to emergency heat mode? does the furnace run and HP never comes on , like it suppose to.

All you got to do is raise your setting on the thermostat to get a higher differential to get the 2nd stage to come on for the furnace, chances the blower speed increases RPM?

Ah ok, sorry for the confusion. What I was referring to when I said that was the picture of the Ecobee settings I posted - I should have clarified "I don't see that connected currently *in the Ecobee app*" - so I'm only referring to what I see there. I haven't removed the t-stat from the wall to check the physical wiring and I haven't gone to the furnace or heatpump to try to look at the physical wiring configurations there either.

What I ultimately want here is to have the ability to switch between gas and electric heat at the thermostat whenever I want. It *sounds* like the system needs to be setup as a true hybrid system in order to do this, where I would basically use the emergency heat mode to run the gas furnace? Or, is there a way to set the hybrid system up so that gas kicks in first as the primary source of heat and heatpump kicks in as the aux/emergency mode when temps get below X-degrees (in this case, I would just set it to be 0-degrees, so then the electric heat would never be used.... at least here in SoCal)

Bazooka Joe · Nov 11, 2022

“is there a way to set the hybrid system up so that gas kicks in first as the primary source of heat and heatpump kicks in as the aux/emergency mode when temps get below X-degrees (in this case, I would just set it to be 0-degrees, so then the electric heat would never be used.... at least here in SoCal) “

You got that backwards if I’m reading it correctly, you want the HP to run on a warmer day as an example only above 35 degrees ( balance point setting ) when the OD temperature goes below that the furnace comes on ( all the while the blower motor is still running ) and the outdoor Heat Pump section shuts off, then when the OD temperature goes above 35 degree ( thermostat still calling for heat ) it switches to HP and furnace is off. If and when the outdoor section fails ( while in heat mode and above the balance point of as this example 35 degree ) you physically change to emergency heat to run 100% gas furnace until repairs are made on the OD section.

jplee3 · Nov 11, 2022

Bazooka Joe said:
“is there a way to set the hybrid system up so that gas kicks in first as the primary source of heat and heatpump kicks in as the aux/emergency mode when temps get below X-degrees (in this case, I would just set it to be 0-degrees, so then the electric heat would never be used.... at least here in SoCal) “

You got that backwards if I’m reading it correctly, you want the HP to run on a warmer day as an example only above 35 degrees ( balance point setting ) when the OD temperature goes below that the furnace comes on ( all the while the blower motor is still running ) and the outdoor Heat Pump section shuts off, then when the OD temperature goes above 35 degree ( thermostat still calling for heat ) it switches to HP and furnace is off. If and when the outdoor section fails ( while in heat mode and above the balance point of as this example 35 degree ) you physically change to emergency heat to run 100% gas furnace until repairs are made on the OD section.

Is that the only way to to have the hybrid system setup? You can't reverse that so that it's "gas first/electric backup"? In my case, I'd want to be using gas all the time if possible (as long as the rates are lower than electric) and then cutover to use electric heat (as emergency/aux or whatever) when the cost of operating gas starts surpassing electric.

Oh btw, regarding the 2nd stage heating. I currently have the t-stat set to a 79F target (it was 68F in here originally). This is what I see from the Ecobee run history:

Doesn't seem like 2nd stage has engaged at all...

Wiring for Carrier 2-stage heatpump/furnace hybrid

jplee3

BNME8EZ

jplee3

Bazooka Joe

jplee3

BNME8EZ

ss120396

FlyersFan

jplee3

Bazooka Joe

BaldLoonie

jplee3

Bazooka Joe

jplee3

Bazooka Joe

jplee3

Bazooka Joe

jplee3

Bazooka Joe

jplee3

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