Honeywell Aube Technologies RC840T-120 Electromechanical Relay with Built In Relay

The Honeywell RC840T-120 Electromechanical Relay is a high-quality solution for controlling electric baseboard heaters, convectors, and fan-forced heaters. Featuring a built-in transformer, it seamlessly connects low-voltage thermostats to high-voltage heating systems, ensuring efficient and consistent operation. Designed for 120V applications, this relay provides quiet switching and reliable performance, reducing electrical noise and wear. Its compact and durable construction makes installation easy in residential and commercial settings. Users appreciate its efficiency, ease of wiring, and compatibility with various heating systems, making it a trusted choice for temperature control solutions.

EDIT: this RC840T-120 works well, no overheating. Have tested with 15A 120V heater with 1400W showing at the kill-a-watt. Using a multimeter, there is 5.6VAC at red LOAD wire, even when thermostat is OFF. Apparently this might be normal OFF voltage, as the other model RC850 manual indicates that the OFF voltage should be <5VAC. So if 5.6V is above the breakdown resistance of the resistor (I think yes for most heaters as it's just a very simple wire?), you will consume 3.6W all the time, even when heater off. Which is 31kWh per year about 50c. I can't tell with the kill-a-watt as the kill-a-watt does not turn on. I use a switch in line, so I can turn off the whole system during the summer. Use gray for that switch and the outlet so it's clear that it's not a normal outlet. It DOES work very easily. Just add black (C common) white (W) & red (R) small wires (I used 14Ga stranded) and join the white and red for the heater to be on. My opinion: DON'T buy a return. Get a NEW one. The "very good" return I was sent did NOT work. The NEW one works great. NO excess heat when running a 15A 120V heater. I have seen more excess heat from a GE extension cord when running 15A than from this. A+++ on the excess heat issue, which is an important issue for me. The other kind of in-line thermostats seem to suffer a lot from excess heat issues (unless people are just wiring the 240V versions wrong, which might be the case. I saw one video where a guy was referring to one of the wires as "neutral") I use another 4 square metal box for it. I don't just hang it off the side of a 4 square box. So I have a 2 gang box with a light switch on the left and a blank on the right and then I have another 2 gang box above that with a blank plate over it, just for this thing and a couple of connections. Although I partly did that because I was anticipating excess heat because you can't even buy an extension cord these days that is rated for 15A that doesn't have excess heat. But there was no excess heat so maybe the hanging it off the side of 4 square box method is OK. Power is proportional to V squared at constant R, so if I was running a pure resistive load, it would consume 0.24% of full power all the time. So 1.5kW resistive heater would consume 3.6W all the time. "if my calculations are correct" For scale, you lose 0.76W in a 2A resistive fuse. So this power loss is like the power loss in 5 fuses. 22A rating is good

This has been working very well for me and was easy to install with the instructions. You should have electrical building experience to install it though. It is installed to a 1900 junction box in my attic and the thermostat wire is ran from the relay down to the Nest thermostat in the bathroom. The Nest thermostat gets the right low voltage to operate and will request the 120 volt circuit to complete through the relay when it calls for heat. The heater is 700 watts. You can schedule the Nest when to call for heat, along with all the Nest options. I'm very happy to have found this relay it was the perfect match and cost for my project. P.S. This is a real review from a real home owner... I will check this review for any questions..

I purchased this relay to operate an electric fireplace using an old programmable thermostat I had laying around. Works like a charm. The selenoid in the relay is audible but not intrusive.

I used this device to connect a Google thermostat to an electric resistance heater.