I bought Honeywell wireless smart thermostat RTH9585WF through the utility company promotion. I put it aside for some time (several months in fact) because it needs C-wire to install. My original thermostat was battery operated smart thermostat, therefore it didn't require C-wire. I knew the 24V AC transformer can provide non-existent C-wire functionality and finally bought this transformer. In order to conceal the transformer (in the attic) and wire, I had to snake the transformer wire through the ceiling and the wall to the thermostat wire hole. That took lots of effort in my case, not the fault of the product design. By the way, wire is long enough for most installation, but if it's not long then you can extend it. Once the transformer wire is out through the thermostat hole, installation is very simple. In my case, Red and White wire is connected to RH and W respectively. RH and RC was jumpered. Now the two transformer wires are connected to C and RC, respectively (polarity doesn't matter). That's it, the wiring is complete. Plug the transformer, Honeywell thermostat powers on. The initial screen stays on until you swipe it across, then the setup screen will appear. Now the star rating--why 4 stars? The wire is very thin and stranded, therefore it doesn't have the strength and rigidity to go through the connection hole in the thermostat terminal. I had to splice different and thicker wire strands to this transformer wire to put it into the terminal. It should have been pre-tinned or thicker, sold wire.

I have a boiler for heating and my old thermostat used just R and W wires. There was a third, common wire, but unfortunately it wasn't hooked up on the boiler end, and wouldn't be easy to fix. This little device made my ecobee3 lite smart thermostat work very easily.

It's inexpensive, and has a little box ("wall wart") that plugs into the wall, and a long cable with two pins. The pins are VERY flimsy which makes them hard to push into the receivers in the ecobee, but it worked well enough. I put the cable along the wall underneath the ecobee housing. I plugged the two pins into RC and C (I put the striped one in RC and the blank one in C... I don't know if that matters but some other reviewers of similar products said to do it that way). Then the original thermostat wires went into RH and W1, and everything is working great.

The little plug-in box doesn't seem to be getting too hot the way some reviewers of similar products have complained. I am taking off a star for (1) flimsy pins (2) a rattling sound in the plug-in box as if something wasn't firmly attached in there. But value for money is definitely there, as long as it keeps working for long enough. (Even replacing it every year or so would be cheaper than doing the electrical work to get the original common wire working.)

Worked as intended and fast delivery

5 stars

Work as expected