24V Thermostat Transformer,AC 24V C-Wire Power Supply Adapter for Honeywell Smart WiFi Thermostat,Nest Learning Thermostat,Emerson Sensi,Ecobee3 Ecobee4 Smart Thermostat (UL Certified,20 Feet)

These older houses are a pain to upgrade with technology! This allowed me to use a honeywell WiFi thermostat without having to run a new thermostat wire with a common wire and probably saved my life in the process. I am not an electrician - best to play it safe!

Long wire, easy enough to feed through back of thermostat faceplate. Thermostat immediately recognized new wiring setup and prompted setup changes. Install was super easy (although unit does not come with instructions, I referred to diagram displayed here in the product images)

My home was built in 2003 without a C wire setup for the air conditioner. This was a much more simpler and cost effective method than calling an HVAC technician to the house and running a wire!

I wish that there was an I'd label for the hot and ground leads. I made assumption, and was right, but it would be nice if the plain and marked wires polarity was confirmed.

When I tested its output it was nominally correct. However, I momentarily accidentially shorted output wires during installation and it stopped working immediately. My fault but seems the product is not very robust. I replaced it with one that was physically much heavier and with an LED status light and that one is working beautifully.

With a transformer, it doesn't matter which lead is positive and which is negative. 24VAC both. Either wire can be the 'C' or the 'Rc'.

Beware, this will not work for Ecobee unless you have a jumper wire. Ecobee needs the RC terminal. This is not included but other products include a jumper wire.

It will power the Nest thermostats, if your HVAC system does not provide the right mix of wires to power it.