Nest + Heat Pump Help Please

[NestCAD]

Hi folks, first time posting for Nest thermostat help. I'll try to keep this brief but it will take a moment. I would greatly appreciate insights on my situation.

Ontario, Canada based so cold temperatures. We had a reno done about 8 years ago and had an air-source Heil heat pump installed outside with a new forced air electric International Comfort Products air handler inside with "electric heat accessory". Simple thermostat installed at the time. All fine.

A couple years later we found we needed remote access for setting temps. I got a Nest thermostat, 3rd generation. The original system installation vendor installed it. Then, in 2018, I had a checkup service call and the tech made some changes. All good, I thought.

Fast forward to recently. I noticed when it was cold, "Alt Heat" came on and the heat pump outside shut off. And, the humidifier did not run whenever "Alt Heat" was on, but worked perfectly when "Heat" was on.  I didn't give it too much thought and thought I would have another routine service visit to sort it out. However, the current insanity since early 2020 has meant that I have tried and have failed to get a service call for the last 18 months so I decided to try to figure this out myself.  My review of settings showed that the system was set up as "Dual Fuel" with white on W1 for "Alt Heat".

My research makes me think I really have a "single fuel" not "duel fuel" system. And that my heat pump should run during the winter and be supplemented by "Aux Heat" as opposed to switching off entirely when "Alt Heat" comes on. And my humidifier should operate both when "Heat" is on and when "Alt" or "Aux" heat is on. 

So, I took a deep breath and had Nest support on the phone this morning and we changed it. She was convinced I have a "single fuel" system and the White wire should be on W2, not W1 where it was. I've attached a picture of the wiring plate AFTER I spoke to Nest and we made a wiring change moving White from W1 to W2. Interestingly, she didn't have me go to Equipment and change the Fuel setting to "Single" but I did that myself based on my own reading afterward.

I have also attached a poor picture of the furnace's wiring panel if that is useful to any of you (apology for the poor clarity).

In my online Nest settings, I now of course have the relevant heat pump options I could not see before today.

Stage 1 and Aux are now "Electric". Before the change today, Stage 1 was Electric and Aux (or Alt) was Gas (!).

Heat type is "Forced Air" for both.

Orientation is "O or B"

Compressor is "Always On"

I set heat pump balance to "Balanced" for now and I set preheat max to 2 hours (I lower the temp a couple degrees overnight for sleeping and raise it back up in the morning).

And I set "Aux Heat" to come on at 20F (-7C), The prior setting before today was for "Alt Heat" to come on at 23F, the point at which the heat pump outside would stop.  I think using "Balance" overrides this setting but if I'm otherwise on the right track, you can perhaps clarify for me.

If you've stuck with me this far, thank you. In summary, can I ask the experts here:

- Do I really have a "Single" fuel system that the 2018 installer tricked into being a "Dual" fuel system in Nest?  Perhaps the tech in 2018 thought he was doing me a good turn and not having the outside unit running all winter supplemented by "aux heat" was cheaper than fooling the system into dual mode and running just "alt heat" when it got really cold. I cannot come up with anything better than that as an explanation.  

- Did I make the correct adjustments to the system today? Moving the White wire to W2, making the Nest recognize this as "Aux Heat" not "Alt Heat". Changing the fuel setting to "Single" and the other things I did above for the heat pump?

- Anything else I need to do or undo?  Maybe the 2018 tech was right and I should put everything back; it just didn't seem right to me.

I would greatly appreciate your feedback as, obviously, I ain't getting a service call anytime soon! Thanks very much in advance!

 

 

[cameronmarcher]

Hi NestCAD,

Unfortunately I don't have answers to your question, but I am asking a similar one. I have an American Standard system with a heat pump and a blower with resistive coils. My Nest (Gen 1) is set up as "dual fuel" with the coils set up as alternate heat. I would prefer that it operate as auxiliary heat instead of alternate. Did your changes work out for you? Thanks!

[NestCAD]

Hi Cameron.  Yes, I made the adjustments I highlighted in the post above and I have been operating my system that way for several months now.  I've concluded that it's "right" and seems to accurately reflect my system and what I should be trying to do with it. 

I made the Heat Pump settings totally manual so I appear to have full control of what the Heat Pump and the Aux Heat do now.  Heat Pump balance is "off".  I have the Compressor lockout set to 15degrees, meaning the Heat Pump will work down to that temp.  I have the Aux Heat lockout set to 25 degrees, meaning Aux Heat should not normally kick in above 25 degrees.  So, between 15 and 25 degrees in this case, the Nest decides what to do.

In practice, things appear to function as follows:

- Normal Heat Pump operation: down to as cold as 15 degrees, with Aux Heat not coming on between 15 and 25 degrees UNLESS the system cannot keep up heating with the Heat Pump alone.  This is exactly what I wanted (or think I want anyway!).  My review of History shows that on the relatively warmer days Aux Heat does not activate at all, which is correct.  On days where temps fall and the Heat Pump alone cannot keep up, Aux Heat kicks in to supplement the Heat Pump.

- Very cold temps, below 15degrees continuously.  On these days, the system seems to also do what is expected.  Aux Heat runs exclusively without the Heat Pump going at all.  When things warm up, they start to work together again.

Note, because the Heat Pump now operates in a broader (lower) range than it did before and doesn't switch as abruptly as it did last year to "Alt Fuel", it operates the humidifier on a more normal schedule as well.  Now, the humidifier is only off when the system is running Aux Heat exclusively.  If the Heat Pump and Aux Heat are working together, the humidifier is on (assuming humidity is required based on how I've set it).  This is a big improvement for me.  The humidifier was off so much of last winter I had to set up portables to keep the air quality where I wanted it.

Hopefully this description of what happened is useful to you.  All the best.

[elucid]

I've been trying to find the option where my heat pump and aux heat run simultaneously. I do not have heat pump balance and I've read that if I have control over my aux heat (W1 or W2), then I will not see this option but will see the "duel fuel" option instead to set at what temp to run the aux heat.

I would like my system to run the heat pump + aux heat when:

a) I call for a temp that is >3 degrees than current temp

b) when outside temp drops below 20 degrees

but it seems my nest thermostat can only call one or the other. If I call for aux heat, my heat pump stops running.

[cameronmarcher]

Hi elucid -  I had this problem as well. My guess is you probably have your thermostat set to dual fuel mode, in which case it uses a preset to switch over to the "alternate heat source." I had it set up like this as well and recently changed it. I have forced air with a heat pump and auxiliary electric strips. I removed the Nest from my account, did a factory reset, and then set it back up without using dual fuel. Now I get the behavior I expect - heat pump is primary source and auxiliary heat comes on to help out.

[elucid]

Thanks! That makes sense because I just switched from a "heat pump+oil" to "heat pump+electric". In a duel fuel system, you would never want your heat pump and oil to be running at the same time.

Do you have single stage alt heat or dual? I have W1, W2, and W3 on my control board. Wondering when and how the nest calls for heat pump+W1 OR heat pump+W1+W2.