Reddit reviews Class II Transformer - 24 Volt AC, 40 VA, UL/CSA Approved : MGT-2440

Sure you can. It'll cost you $14:

https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA

Transformer input: 120VAC, 60 Hz (standard US)

Transformer output: 24VAC, 25VA

"VAC" means Volts AC. This transformer outputs AC current, not DC. "VA" is Volt-Amps, which is basically the power output.

Here's one on Amazon that would probably work:

http://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA/ref=sr_1_5?ie=UTF8&qid=1462551934&sr=8-5&keywords=ac+transformer+24v

It's a bit of overkill at 40VA, but like I said, I think it would work just fine.

But this one will work:

https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA

Well, first thing, don't trust the standard wire colors on this installation.

That being said, if you want to use the existing wiring, you can get 24v to your 'C' terminal with one of these:

https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA

Your call. The most difficult would be to pull new t-stat wire from your A/C to the best position that you want for the Ecobee.

I like your chosen t-stat because it can pair with remote sensors, for added efficiency. And you can connect it to your home network. It is a good choice.

I'm making the assumption you're in the US. So if I'm wrong, some of this will be too.

Ring has a plug-in adapter that can be used with (only) the Pro and has 20ft of cable for people without existing wiring so you don't have to involve an electrician https://shop.ring.com/products/plug-in-adapter

If you want to wire to an existing power source, you'd be looking at installing a big Nutone C907, which is bigger than a single gang (single switch or outlet width) electrical box and looks like this. Being that you're asking this question in the first place, that's probably not something I'd recommend undertaking by anyone other than a qualified electrician, as this is a lot more than just turning off the power and swapping out an old transfomer for a bigger one.

I'd go with the power adapter and plug it into an outlet.

(And just FYI I have zero affiliation with Ring, so I'm not promoting that link for any reason other than it's the only safe plug in adapter for the Pro, as those ones you see on Amazon don't even come close to supplying enough power, and will burn out the Ring and/or the adapter, and by the time it happens in a month, it will be too late to return—those ones on Amazon, no matter what they say, are not OK with the Pro.)

If you need something longer than 20 ft but don't want to call an electrician, I'd recommend this, and only this, off Amazon. https://smile.amazon.com/gp/aw/d/B004VMVDTA/ (full link so you can see no afilliate or referral links) which you can use with your own 18-22AWG SOLID bell wire. 22AWG solid core for up to about 30 ft, 20AWG from 30-50 (or 0-30 ft if stranded not solid wire), and 18AWG solid (only, don't use stranded beyond 30ft) if you need to get up to 75 ft, but I wouldn't go much beyond that with low voltage wiring.

OK, do you have easy access to the boiler 24vac transformer? If not, you need to buy a plug-in like this: https://smile.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA/ref=sr_1_1?ie=UTF8&qid=1523549249&sr=8-1&keywords=plug+in+24vac+transformer
The new wiring scheme will be this: Receiver Red connect to current boiler Red terminal. Receiver White connect to current boiler White terminal. Disconnect current boiler Red wire and connect to boiler or plug-in transformer R. Disconnect current boiler White wire and connect to Receiver Purple. Connect Receiver Black to boiler or plugin-transformer Common terminal. Don't touch AC Red, Yellow, Green on the AC/Boiler side. Now go to the thermostat side. Connect Red from AC to Ecobee Rc. Connect Sender Purple to old Boiler White. Connect Sender White to ecobee W1. Connect Sender Black to ecobee C. Connect AC Y to ecobee Y1. Connect AC G to ecobee G. Connect old boiler Red wire to ecobee Rh.

Mine is wired in directly using this

Works perfect for me and registers a solid power rating in the app.

Well, since all four wires to the t-stat are spoken for, you can pull another wire, or cheat:

https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA

T-stat does not care where the power comes from. Does not have to be the furnace or A/C.

It looks like your best bet to power the Ecobee is to buy one of these or similar. It won't be the best cosmetic solution, but it will function well.

I actually ended up getting it to work with this.

Hey, wow didn't even know about inbox replies. Appreciate it

I purchased the same 24v relay but with the ground: https://www.amazon.com/gp/product/B004VMVDTA/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
And this ice cube relay:
https://www.amazon.com/gp/product/B00PZXGHZY/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

I used your wiring scheme and it worked fine (then I unplugged and let die) but I was just testing without it hooked to my HVAC system and was able to get the relay to engage. Now after plugging back in I am getting a variety of wiring errors and the nest restarting.

Let me know if you think it is diagnosable or should provide more info. Appreciate the help.

Yes this is what I did. You're going to need to run additional wires to your thermostat. There's no way around that. What I used is this 24V transformer and this 2 conductor thermostat wire. One end goes to the two power terminals on transformer (nothing gets connected to ground) and the other end goes to RC and C on the Ecobee. It doesn't matter which one is which since it's A/C voltage. Your already existing heating wires go to RH and W1.

Just bought one of these https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA/ref=sr_1_4?ie=UTF8&qid=1481043700&sr=8-4&keywords=class+2+transformer

And bought some new thermostat wire - https://www.amazon.com/Coleman-Cable-Thermostat-18-Gauge-5-Conductor/dp/B0026H8L7E/ref=sr_1_2?ie=UTF8&qid=1481044119&sr=8-2&keywords=thermostat+wire+18+5

I split the thermostat cable so that I could run two of the wires to where I plugged the transformer in, near my furnace, connected two new wires to the furnace and then used the old thermostat wire to run the whole new wire up to the thermostat location. Of course you could just leave your existing wires in place and only run the new wires for the transformer... but I found using the old wire and pulling it through was the only way I could run the new wire anyway.

Then connect the wires... I forget which terminals I've used, will have to look tonight when I get home.

Was it just a 24v wall transformer, something like https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA ?

Corner cutting... Not a severe hazard with LV wiring, but just kind of a cruddy thing to do. Older furnace?

I'm using a 24VAC 40VA transformer for my hello, and it's the only thing on the wire.

Honestly, I'd probably get a more powerful transformer. They're relatively inexpensive. If you have experience working with 120VAC, you can get very inexpensive transformers. If not, or you don't want to mess with it, you can get plug-in transformers for a bit more that have the same little screw terminals, and you can just move the wire, assuming there's an outlet near enough to reach.

I got mine on amazon for $20, they're cheaper than that now.
Here's the link to the one I got, but there are lots of options...

https://www.amazon.com/Class-II-Transformer-Approved-MGT-2440/dp/B004VMVDTA/

EDIT: And just to add:

I had a lower power 16vac transformer originally (slightly above minimum spec for the Hello, and had problems with the Nest -- Chime wouldn't work, and would buzz instead of ding.) The chimes themselves have a pretty good power draw, so often the minimum spec for the Hello not enough (or barely enough) unless you're not using a chime on the circuit.