topic Re: Installing nest thermostat with no "c" terminal on furnace in Nest Thermostats

Installing nest thermostat with no "c" terminal on furnace

Bfigeroa — Sun, 04 Feb 2024 23:54:16 GMT

Hi, I hope someone can help me. I've been wanting to install a nest thermostat but I've been reading about the problem with the common wire "C" (apparently is not that common since I think the majority of houses do not have this wire). Any how... I read about different suggestions but I want to stick with the official from Google.

I'm my case is an older furnace/boiler that do not have a "C" terminal and for this Google installation instructions refer to the installation pros.... which includes getting an external transformer and remove the jumper in the Google nest power connector.

My question is very simple. Will the following transformer do the trick for this specific scenario?

https://a.co/d/3eTnLrK

Thanks in advance.

Re: Installing nest thermostat with no "c" terminal on furnace

CoolingWizard — Tue, 06 Feb 2024 09:56:15 GMT

@Bfigeroa , that transformer will not work for you. What you need to be carful of is what power control system does your furnace use? Is it based on 24VAC or is it 750mA system.

AC Cooling Wizard

Re: Installing nest thermostat with no "c" terminal on furnace

Bfigeroa — Tue, 06 Feb 2024 13:27:18 GMT

Hi @CoolingWizard, thank you for taking your time to answer my question.

How do I find out what system is?

My control panel is a Honeywell (aquastat) L8148A.

I already took my chances and installed the nest with that adapter following the instructions from the nest connector installation pro and it seems to be working, but I will appreciate your comments and if this is something wrong please let me know. I don't want to damage the boiler.

Thank you.

Re: Installing nest thermostat with no "c" terminal on furnace

CoolingWizard — Tue, 06 Feb 2024 22:06:46 GMT

@Bfigeroa , the aqua stat is nothing more than a boiler controller with a built-in transformer and except 120 to 240 V of AC power to control it. There are simple two connector for thermostat known as T and T or T1 and T2. a two thermostat connections are simply more than a contact. When T1 and T2 are connected to each other or when T is connected to T, the Aquastat will turn on the boiler. If you want to use a Nest and power it. Use a 24 volt AC transformer, wire to RC and C. Then wire the Aquastat to Rh and W1.

AC Cooling Wizard