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Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 08:04AM
Hi everyone,

Just got around to installing a Sensi thermostat that I got (can't remember if I got it as part of an energy efficiency package, or just on sale) ... installation went pretty easily, and it replaced a Honeywell -- nothing wrong with the Honeywell, and in fact it's a very good thermostat, just not a "smart" one.

My question is -- coming from the wall, there was a blue wire labeled "C" with a paper label, but it wasn't attached to any of the Honeywell's terminals (in fact, there doesn't seem to be any "C" terminal on the Honeywell at all). The Sensi does have a C terminal, so should I connect this wire?

TiA




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
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Re: Question re thermostat wiring
Posted by: Ombligo
Date: July 25, 2021 08:13AM
In general, you need a C connection on smart thermostats. So I would suggest going to the other end and seeing if the blue wire is hooked up at that end. If it is hooked up to the C there, then do likewise at the thermostat.



“No persons are more frequently wrong, than those who will not admit they are wrong.”
-- François de La Rochefoucauld

Growing older is mandatory. Growing up is optional.
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Re: Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 08:14AM
Quote
Ombligo
In general, you need a C connection on smart thermostats. So I would suggest going to the other end and seeing if the blue wire is hooked up at that end. If it is hooked up to the C there, then do likewise at the thermostat.

You mean following the blue wire all the way back from the wall to wherever it connects at the AC controller?

It'd probably just be easier for me to connect the wire and see what happens. grinning smiley




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
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Re: Question re thermostat wiring
Posted by: Ombligo
Date: July 25, 2021 08:30AM
Just go to the furnace/heat pump/air conditioner and look at the connections. The colors will be the same.



“No persons are more frequently wrong, than those who will not admit they are wrong.”
-- François de La Rochefoucauld

Growing older is mandatory. Growing up is optional.
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Re: Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 09:25AM
Quote
Ombligo
Just go to the furnace/heat pump/air conditioner and look at the connections. The colors will be the same.

Right, but how would I know on the heat pump/air conditioner, to what the blue wire connects?

Edit: in the time since I wrote this, I went ahead and connected the blue wire to the Sensi. Seems to be working fine?




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
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Re: Question re thermostat wiring
Posted by: Ombligo
Date: July 25, 2021 10:51AM
The connections are labeled the same as the thermostat.



“No persons are more frequently wrong, than those who will not admit they are wrong.”
-- François de La Rochefoucauld

Growing older is mandatory. Growing up is optional.
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Re: Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 10:56AM
OK ... I can now verify that it is indeed working fine, but I have a followup question.

The Sensi is also reporting humidity, which of course is relatively high. It has an option to dehumidify by way of overcooling, which it says it will overcool up to 3 degrees below the set temp in order to remove excess humidity.

So ... does it make more sense to set the dehumidification feature (with a higher setpoint), or to just leave the temperature set at the lower setpoint but without dehumidification? (I could potentially also get a separate dehumidifier, but around here, that thing would probably have to be running 24/7 to make any difference -- unless it was a whole house model, which would probably increase my electricity bill for exactly the same reason.)




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)



Edited 2 time(s). Last edit at 07/25/2021 11:01AM by PeterB.
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Re: Question re thermostat wiring
Posted by: GGD
Date: July 25, 2021 11:09AM
The "C" wire just provides power and doesn't control anything in the HVAC system, if the thermostat still works with it's batteries removed, then the C wire is connected correctly.
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Re: Question re thermostat wiring
Posted by: Altered Horizons
Date: July 25, 2021 03:27PM
Did you download the Sensi iPhone App? It's suppose to to walk you through the setup. I did the wiring first, so I skipped that part.

There's also setup info on their website. Here's a couple of links:

Wiring Sensi Thermostat

Sensi Smart Thermostat (scroll down a bit for a video and "Learn More").

I also downloaded installation and user manual pdfs from their site (sorry, I don't have the links for these).



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myHouse: [alteredhorizons.no-ip.org]
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Re: Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 03:36PM
Yep, I did the whole install through the app's walkthrough.

It does seem to work fine now, but like I said above, I'm debating how to set things to get the best balance of comfort vs. electrical expense.




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
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Re: Question re thermostat wiring
Posted by: modelamac
Date: July 25, 2021 05:29PM
The AC will do a bunch of dehumidifying on its own, so why not experiment without setting a humidity level????????????????



Ed (modelamac)

I think I will just put an OUT OF ORDER
sticker on my head and call it a day.
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Re: Question re thermostat wiring
Posted by: PeterB
Date: July 25, 2021 06:54PM
Quote
modelamac
The AC will do a bunch of dehumidifying on its own, so why not experiment without setting a humidity level????????????????

That's what I might try ... I'm just curious if I'll be able to tell a difference in usage between, say, 75 degrees with dehumidification, versus 72 degrees without.

Interestingly, there's actually very little on Sensi's website about how this setting might affect your energy bill: [sensi.emerson.com]




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)



Edited 1 time(s). Last edit at 07/25/2021 06:56PM by PeterB.
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Re: Question re thermostat wiring
Posted by: Carm
Date: July 25, 2021 07:36PM
Each setup is different, obviously a rise in cost. Difference depends on a lot of factors. It’s over 110 most days here in SoCal desert, but we set the AC to 77 and we can tell the humidity when we head outside. My wife sets the A/C for the bedrooms at 72 during the night. Not much of a price difference, but we are not on SoCal Edison but instead on IID (Imperial Irrigation District) which has a lower rate. (Two A/C units)



Edited 1 time(s). Last edit at 07/25/2021 07:38PM by Carm.
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