Help to identify wiring in old thermostat

Hi,

We just bought a house.
This house has a fairly old dual fuel heating/cooling system (york heat pump and oil furnace) with a york thermostat using mercury.
I attached the picture of the thermostat without the cover.
I'd like to change it for a Nest learning thermostat and sent the picture to Nest support.
From the picture I have attached, they are unable to determine if your system is compatible.
I need to remove the thermostat from the wall to expose the wire terminals. I really don't want to do this since I don't want to break anything.

Is there somebody on this forum that could give me some info regarding my thermostat; serial number, serie or even better wiring schematics ?

Thanks a lot in advance

Pascal

Nest has a concierge service that includes the cost of having a professional come install the 'stat.

The thermostat in your picture is capable of 2 stages each for heating and cooling. Do you have a heat pump or an air conditioner? (If one the switches has an emergency position or "em heat" you likely have a heat pump.) Do you have a gas furnace or an electric furnace?

The nest cannot do dual-fuel, which is a heat pump coupled with a fossil fuel furnace. If your system is NOT dual-fuel then you can most likely use the Nest.

My preference is the Honeywell Prestige thermostat with Red-link gateway for internet connectivity. I have only dealt with the Nest twice, though, so I can't make a judgement regarding that one.

Quote:

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Originally Posted by kdean1

Nest has a concierge service that includes the cost of having a professional come install the 'stat.

The thermostat in your picture is capable of 2 stages each for heating and cooling. Do you have a heat pump or an air conditioner? (If one the switches has an emergency position or "em heat" you likely have a heat pump.) Do you have a gas furnace or an electric furnace?

The nest cannot do dual-fuel, which is a heat pump coupled with a fossil fuel furnace. If your system is NOT dual-fuel then you can most likely use the Nest.

My preference is the Honeywell Prestige thermostat with Red-link gateway for internet connectivity. I have only dealt with the Nest twice, though, so I can't make a judgement regarding that one.

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That thermostat can't do dual fuel either. So there must be a dual fuel control somewhere also.


OP. In order to tell you the serial number of that thermostat, we would have to be able to see the serial number.

Should be interesting when the Nest goes into set back and then tries to raise the temp in the house when the outdoor temp is just above balance point. Will probably take hours to recover.

Kdean1, thanks a lot for your quick reply.

My system is dual-fuel: heat pump (york) and oil furnace. And the thermostat has an em heat switch.
Nest now supports (since 2nd generation) dual fuel systems.
Nest concierge service will still charge me 99$ if it's not compatible.
Once I know fir sure my system is compatible with Nest I'll definitively buy concierge service.
Can you give me a hint so I can start my own research to see if it's compatible ?

I'll take a look at Honeywell Prestige thermostat with Red-link gateway, thanks.

Thanks

Pascal

Take a look @ Ecobee also. Since you have a dual fuel system I would recommend professional installation, make sure the installer is familiar with dual fuel setups.

That is a fairly common thermostat. It is a Honeywell T874-G. If you loosen up those 2 flat head screws in the bottom corners you can lift off the thermostat from the sub-base. Then you will see what wires you have and where they are connected.

https://customer.honeywell.com/resou...0s/60-2485.pdf

Quote:

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Originally Posted by paskos

Kdean1, thanks a lot for your quick reply.

My system is dual-fuel: heat pump (york) and oil furnace. And the thermostat has an em heat switch.
Nest now supports (since 2nd generation) dual fuel systems.
Nest concierge service will still charge me 99$ if it's not compatible.
Once I know fir sure my system is compatible with Nest I'll definitively buy concierge service.
Can you give me a hint so I can start my own research to see if it's compatible ?

I'll take a look at Honeywell Prestige thermostat with Red-link gateway, thanks.

Thanks

Pascal

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From the information you have provided and the most recent information from Nest it appears that the Nest is compatible with your system.
http://support.nest.com/article/Is-N...ooling-systems

My biggest complaints with the Nest is that the instructions for installation are not specific and that the function of each of the terminals are not readily evident. Perhaps that is because I have only dealt with two of them. However, with other more conventional thermostats I don't have that problem.

One of my regular customers has a Nest on one of his systems and a Prestige on his other system. He will be giving me his impressions of both thermostats but he needs time to use them and learn them.

Thank you very very much ammoniadog for the info.

Although the branding is York my guess is York had a partnership with Honeywell.

have a honeywell prestige with a outdoor sensor installed, the are a very good dual fuel thermostat

Honeywell made those stats for dozens of different companies back in the 1980's & 90's. It was actually very common on some of the first generation heat pumps and old Lennox 2 speed systems. Usually they were wired with at least 8 wires and sometimes more. You won't hurt a thing by pulling the old stat and looking. It comes in three pieces, a cover, the actual stat and the sub-base which is mounted to the wall. In it's day it was about the best option out there.

As far the Nest goes, the cool factor is off the scale. I like the adaptive smart algorithms. They claims it works in 99% of installations without a common wire which you most likely have anyway and even if you don't there are ways around that. It pretty much installs like any other stat. I would use their recommended install service especially for dual fuel. Wisely, they make no claims about actual energy savings because that's impossible to predict. So at $249 and $119 for their install it's not really too bad. The hidden light sensors are just plain nifty.

Let us know how it works out for you.