Emerson90 380 Fan Relay 24 Volt Coil, 1

Used this relay in conjunction with a transformer to power a Nest thermostat that controls a millivolt Vermont Casting propane stove. Works perfectly. The stove wires connect to the load side on the bottom two tangs. The white wire from the thermostat (switched) connects to one side of the power on the relay and a wire from the transformer connects to the other. Then a blue and red wire from the transformer connect to common and R on the nest.

Update - December 2022:This relay worked reliably for roughly 3.5 heating seasons. Recently, there were two separate instances where it would audibly click when my thermostat came on but the boiler side wasn’t being connected. I tested the boiler wiring directly and it fired up immediately.Since the relay appeared to be the most likely culprit, I replaced it with a spare one I had which immediately worked as expected.I’m satisfied for how long it lasted. I would recommend buying 2 at a time to just always have a spare if you’re ever using it for something like a Nest.The original seemed to fail when the heat was cycling more than usual as well. Guessing it sped up what was inevitable.Otherwise, my original rating still applies. These are simple and easy to use with a pretty decent lifespan.——————Original Review - October 2019This little relay is cheap but quality. I got this to use in tandem with a 24v hardwired transformer to control my millivolt boiler. Since my current system had no C wire and was just the Rh/W wires to turn the heat on, I couldn't just plug in my Nest.After some research, it seemed like the safest way to add a 24v power supply would be to use a transformer and a relay. Some tutorials claim plugging in the two transformer wires into the C and Rc ports on the Nest will get it to work (which it will) but you run the risk of the Nest sending the 24V of power down to your millivolt system which would not be good.To get around that, I wired up my transformer then ran the Rh wire to the thermostat and the W wire from the thermostat to this relay on the control end then back to the transformer to complete the circuit. Then just plugged in the Red and White wires coming from my boiler into the controlled side of the relay. Completely eliminated the possibility of the two different voltages crossing and messing anything up on my ancient heating system. I also ran an additional wire for the C and Rc ports to provide continuous power but that's not necessary in this setup, just peace of mind for me.Now that it's been getting cold, this relay has been tested without a problem. The Nest kicks on to call for heat and the relay gives a reliable click with the heat kicking on immediately.Just keep in mind this is a physical relay so the click is going to pretty audible. If you don't want to hear it, put it somewhere tucked away. If you're not a fan, you can find a solid state relay that should do the same thing.

I installed this relay to take care of a problem I had with my thermostat turning heat on on my furnace. I was getting a system protest mode error and a note to install isolation relay. Everything works now that I installed this relay.

Perfect match for my new Ecobee smart thermostat. My boiler does not have a transformer or modern R/W/C etc connections, it has T/T connections compatible with the old mercury thermostats. Pair this with a 24v transformer and my new school thermostat works great!

I purchased this for a furnace and it was not an exact fit, but a very simple fix and it works great, especially for the money. Cheap and effective replacement.

seems ok

This was exactly what we needed for our AC unit. It came very quickly and was easy to install!

I hope the picture helps you.I'm adding a photo of the wiring diagram and a quarter for sizing, since the label is not shown on Amazon. The description leaves us to search the web for the actual specs.Good price, form factor, and flexible hook-ups.Performance update: I've use 4 of these for a month and they work fine. I was worried about chatter noise based on another review, but mine are quiet except the click to change pull in the contacts. It's likely the power supply of the other reviewer was underpowered and couldn't hold the contacts in securely. When the contacts are pulled in the unit is a few degrees above ambient - slightly warmer than surrounding areas.